Talking of analogue devices and radio interference

Post by Brian Gaff
I have an amplified Sub woofer, but it seems to be very prone to picking
stuff up. For example, it can pick up switching transients and up until
quite recently, even Radio China International. The Chinese seem to have
lowered their power recently, but back when I first got it, you could hear
Vatican Radio as well, but these days they don't use short waves. Its
interesting to note it does not pick up Premier radio, even though there is
an am outlet less than a mile away.
We tried mains filters internal capacitors everywhere with no effect. It
even did it connected just to the mains and no inputs. I can only deduce
that the power amp design is just wide open and allows most stuff into the
amp where it just gets rectified and shoved out through the speaker.
I once had a Tandberg tuner amp that was like this, and no amount of
suppression would work there either.
Brian

In most all instances of this type of radio pickup its being demodulated
in around the first semiconductor base emitter junction it finds!.

Bypassing the junction with say a 1000 pf ceramic cap will cure that, it
works much better than all the ferrite beads and the like. A few k ohms
in line with that base junction as long as its not in the biasing chain
will help as well.

Seen this in a lot of TV audio cars even since waay back on 27 MHz AM CB
systems and mobile phone breakthrough the thermostat arcing the lot!!

--
Tony Sayer

Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.

Adrian Caspersz

2023-07-21 13:28:54 UTC

Post by tony sayer
In most all instances of this type of radio pickup its being demodulated
in around the first semiconductor base emitter junction it finds!.
Bypassing the junction with say a 1000 pf ceramic cap will cure that, it
works much better than all the ferrite beads and the like. A few k ohms
in line with that base junction as long as its not in the biasing chain
will help as well.

I seem to remember an industry meddling EU rule that made compulsory the
installation of those capacitors.

Some folks paid extra for them to be removed ....

--
Adrian C

Brian Gaff

2023-07-22 10:50:14 UTC

Oh yes this was the golden ears folk, they wanted DC to Light bandwidth, but
we all know about the wider the window is open the more the muck flies in It
was these same people who loved the quality of radio 3, when the bandwidth
had a brick wall filter at 15khz. I built a stereo decoder that had no such
mpx filter. When recorded on a reel to reel deck and slowed down you could
clearly hear the 19khz pilot tone.
Those were the days, when audio was understandable and you could
demonstrate what was going on.
Brian
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Post by Adrian Caspersz

I seem to remember an industry meddling EU rule that made compulsory the
installation of those capacitors.
Some folks paid extra for them to be removed ....
--
Adrian C

tony sayer

2023-07-22 14:53:46 UTC

Post by Adrian Caspersz

I seem to remember an industry meddling EU rule that made compulsory the
installation of those capacitors.
Some folks paid extra for them to be removed ....

And why might they have done that then?...

--
Tony Sayer

Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.

Brian Gaff

2023-07-22 10:45:52 UTC

I'm sure we tried that as well. It worked on a tape recorder, but not on
other things. Indeed, those with long memories will recall the Sinclair IC12
amplifier chips. I built a couple of these for stereo in my little bedroom
when I was younger. They persistently picked up radar pulses from the
industrial estate down the road. Scanning for these put them in between band
4 and 5 where videos used to live as well. Nothing else was picked up. I had
to replace one due to a short in the speaker blowing it up and it was then
made by Texas and still had the same problem, but later on making the power
section use ILP modules got rid of it. One has to imagine that the IC was i
n fact a glorified op amp of course, and had many more transistors in a very
small area than you needed for the gain you used, so many more chances to
pick up crud.
Brian
--
--:
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
***@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!

In most all instances of this type of radio pickup its being demodulated
in around the first semiconductor base emitter junction it finds!.
Bypassing the junction with say a 1000 pf ceramic cap will cure that, it
works much better than all the ferrite beads and the like. A few k ohms
in line with that base junction as long as its not in the biasing chain
will help as well.
Seen this in a lot of TV audio cars even since waay back on 27 MHz AM CB
systems and mobile phone breakthrough the thermostat arcing the lot!!
--
Tony Sayer
Man is least himself when he talks in his own person.
Give him a keyboard, and he will reveal himself.

2023-07-22 14:18:44 UTC

Post by Brian Gaff
I'm sure we tried that as well. It worked on a tape recorder, but not on
other things. Indeed, those with long memories will recall the Sinclair IC12
amplifier chips. I built a couple of these for stereo in my little bedroom
when I was younger. They persistently picked up radar pulses from the
industrial estate down the road. Scanning for these put them in between band
4 and 5 where videos used to live as well. Nothing else was picked up. I had
to replace one due to a short in the speaker blowing it up and it was then
made by Texas and still had the same problem, but later on making the power
section use ILP modules got rid of it. One has to imagine that the IC was i
n fact a glorified op amp of course, and had many more transistors in a very
small area than you needed for the gain you used, so many more chances to
pick up crud.

The ultimate *visible* RFI was on the news reports from the warships in
the Falklands War. To begin with, the reports were always preceded by an
apology for the poor picture quality - because the ship's rotating radar
pulse stomped a great big noise bar over the picture every couple of
seconds. Of course film would have been immune but there would have been
the "little" problem of taking a film-processing system and telecine ;-)

ENG cameras have to be immune to all *normal* RFI, but immunity from a
megawatt of SHF from a radar wouldn't have been tested for ;-)

Don't know whether it affected the electronics as such (amplifiers etc)
or whether it buggered up the electron beams inside the plumbicon tubes
- because the early 80s were almost certainly before solid-state sensors.

charles

2023-07-22 15:00:01 UTC

Post by Brian Gaff
I'm sure we tried that as well. It worked on a tape recorder, but not
on other things. Indeed, those with long memories will recall the
Sinclair IC12 amplifier chips. I built a couple of these for stereo in
my little bedroom when I was younger. They persistently picked up radar
pulses from the industrial estate down the road. Scanning for these put
them in between band 4 and 5 where videos used to live as well. Nothing
else was picked up. I had to replace one due to a short in the speaker
blowing it up and it was then made by Texas and still had the same
problem, but later on making the power section use ILP modules got rid
of it. One has to imagine that the IC was i n fact a glorified op amp
of course, and had many more transistors in a very small area than you
needed for the gain you used, so many more chances to pick up crud.

The ultimate *visible* RFI was on the news reports from the warships in
the Falklands War. To begin with, the reports were always preceded by an
apology for the poor picture quality - because the ship's rotating radar
pulse stomped a great big noise bar over the picture every couple of
seconds. Of course film would have been immune but there would have been
the "little" problem of taking a film-processing system and telecine ;-)
ENG cameras have to be immune to all *normal* RFI, but immunity from a
megawatt of SHF from a radar wouldn't have been tested for ;-)
Don't know whether it affected the electronics as such (amplifiers etc)
or whether it buggered up the electron beams inside the plumbicon tubes
- because the early 80s were almost certainly before solid-state sensors.

This also happened on the Apollo splashdowns. Cameras on a US aircraft
carrier

--
from KT24 in Surrey, England - sent from my RISC OS 4té
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

wrightsaerials@aol.com

2023-07-25 00:53:29 UTC

Post by Brian Gaff
I'm sure we tried that as well. It worked on a tape recorder, but not
on other things. Indeed, those with long memories will recall the
Sinclair IC12 amplifier chips. I built a couple of these for stereo in
my little bedroom when I was younger. They persistently picked up radar
pulses from the industrial estate down the road. Scanning for these put
them in between band 4 and 5 where videos used to live as well. Nothing
else was picked up. I had to replace one due to a short in the speaker
blowing it up and it was then made by Texas and still had the same
problem, but later on making the power section use ILP modules got rid
of it. One has to imagine that the IC was i n fact a glorified op amp
of course, and had many more transistors in a very small area than you
needed for the gain you used, so many more chances to pick up crud.

The ultimate *visible* RFI was on the news reports from the warships in
the Falklands War. To begin with, the reports were always preceded by an
apology for the poor picture quality - because the ship's rotating radar
pulse stomped a great big noise bar over the picture every couple of
seconds. Of course film would have been immune but there would have been
the "little" problem of taking a film-processing system and telecine ;-)
ENG cameras have to be immune to all *normal* RFI, but immunity from a
megawatt of SHF from a radar wouldn't have been tested for ;-)
Don't know whether it affected the electronics as such (amplifiers etc)
or whether it buggered up the electron beams inside the plumbicon tubes
- because the early 80s were almost certainly before solid-state sensors.

This also happened on the Apollo splashdowns. Cameras on a US aircraft
carrier

It used to happen anywhere near Filton and over a lot of N Yorks near Fylingdales, if a masthead amp was in use.

Bill

2023-07-25 05:49:26 UTC

Post by ***@aol.com
It used to happen anywhere near Filton and over a lot of N Yorks near Fylingdales, if a masthead amp was in use.

When you visit Fylingdales you are warned not to lock your car because
of the number of people who find their car's remote locking is jammed by
the RF levels.

Woody

2023-07-25 08:07:58 UTC

Post by ***@aol.com
It used to happen anywhere near Filton and over a lot of N Yorks near
Fylingdales, if a masthead amp was in use.

When you visit Fylingdales you are warned not to lock your car because
of the number of people who find their car's remote locking is jammed by
the RF levels.

Many people do not realise that Fylingdales and its associates work in
the 420-450MHz band*: car keys used to use 433.92MHz (right in the
middle of the 70cms amateur radio band of 430-440MHz) but many now use
frequencies in the 860MHz area.

Fylingdales was not so much of a problem. When the emergency services
started using Airwave at 380/390MHz and digital the number of calls to
the AA from drivers unable to get into their cars at Heathrow
sky-rocketed. The aerials were placed on the roof of the car parks to
give better coverage for car theft but it seemed to occur to no-one that
the increased noise floor could affect keyless car entry!

*About (cough) years ago we were driving back from a day trip to Whitby
over Fylingdales Moor when a small female voice in the back seat
suddenly piped up
"Look Mummy, eggs."
That is still a joke in our house to this day (Fylingdales was then
still the geodesic domes.)

2023-07-26 06:51:53 UTC

Post by Woody
Many people do not realise that Fylingdales and its associates work in
the 420-450MHz band*: car keys used to use 433.92MHz (right in the
middle of the 70cms amateur radio band of 430-440MHz) but many now use
frequencies in the 860MHz area.
Fylingdales was not so much of a problem. When the emergency services
started using Airwave at 380/390MHz and digital the number of calls to
the AA from drivers unable to get into their cars at Heathrow
sky-rocketed. The aerials were placed on the roof of the car parks to
give better coverage for car theft but it seemed to occur to no-one that
the increased noise floor could affect keyless car entry!

I asked at Fylingdales what frequency it operated on and was told it was
secret! Obviously never heard of scanners or spectrum analysers.

With those levels of RF, the frequency is probably irrelevant with most
receivers.

There used to be remote car keys operating on a lot of different
frequencies (one of our vehicles at work had an illegal one!). But
probably not a problem now that most are factory fitted.

2023-07-26 10:44:22 UTC

I asked at Fylingdales what frequency it operated on and was told it was
secret! Obviously never heard of scanners or spectrum analysers.
With those levels of RF, the frequency is probably irrelevant with most
receivers.
There used to be remote car keys operating on a lot of different
frequencies (one of our vehicles at work had an illegal one!). But
probably not a problem now that most are factory fitted.

The real problem is those cars that have no mechanical keyhole (or else one
that needs tools to access in an emergency), where you can only use the
remote. I'm used to one of my car keys (I keep it as the spare) not
operating the central locking (yes I've replaced its battery!) and so having
to lock/unlock the doors the old-fashioned way when Ii take the car to the
garage to be serviced. And I warn them, though I imagine they are used to
central locking failing for whatever reason and know how to use the key
blade.

And if the RF is so strong that it even affects the key-ECU comms for the
immobiliser, then you are totally stuffed. I presume the only way around
that is to tow the car far enough away that the key and immobiliser can talk
and so negotiate to enable the engine.

tony sayer

2023-07-26 13:58:18 UTC

In article <u9qtdm$1fit9$***@dont-email.me>, NY <***@privacy.invalid>
scribeth thus

I asked at Fylingdales what frequency it operated on and was told it was
secret! Obviously never heard of scanners or spectrum analysers.
With those levels of RF, the frequency is probably irrelevant with most
receivers.
There used to be remote car keys operating on a lot of different
frequencies (one of our vehicles at work had an illegal one!). But
probably not a problem now that most are factory fitted.

The real problem is those cars that have no mechanical keyhole (or else one
that needs tools to access in an emergency), where you can only use the
remote. I'm used to one of my car keys (I keep it as the spare) not
operating the central locking (yes I've replaced its battery!) and so having
to lock/unlock the doors the old-fashioned way when Ii take the car to the
garage to be serviced. And I warn them, though I imagine they are used to
central locking failing for whatever reason and know how to use the key
blade.
And if the RF is so strong that it even affects the key-ECU comms for the
immobiliser, then you are totally stuffed. I presume the only way around
that is to tow the car far enough away that the key and immobiliser can talk
and so negotiate to enable the engine.

Begs the question what do the staff at Fylingdales use for transport?,

push bikes?...

--
Tony Sayer

Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.

J. P. Gilliver

2023-07-26 17:19:23 UTC

In message <***@bancom.co.uk> at Wed, 26 Jul 2023 14:58:18,
tony sayer <***@bancom.co.uk> writes
[]

Post by tony sayer
Begs the question what do the staff at Fylingdales use for transport?,
push bikes?...

Not the same question, but I remember hearing/seeing somewhere that at
certain oil (gas?) refinery sites, conventional vehicles were not
allowed, especially diesel ones, because the air was sufficiently
flammable that even if you turned the ignition off, the engine would
race, to the extent of flames coming out of the exhaust; vehicles for
use on the site had to be modified in some way.

--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)***@T+H+Sh0!:`)DNAf

By most scientific estimates sustained, useful fusion is ten years in
the future - and will be ten years in the future for the next fifty
years or more. - "Hamadryad", ~2016-4-4

2023-07-27 10:17:45 UTC

Post by tony sayer
Begs the question what do the staff at Fylingdales use for transport?,
push bikes?...

Not the same question, but I remember hearing/seeing somewhere that at
certain oil (gas?) refinery sites, conventional vehicles were not allowed,
especially diesel ones, because the air was sufficiently flammable that
even if you turned the ignition off, the engine would race, to the extent
of flames coming out of the exhaust; vehicles for use on the site had to
be modified in some way.

I saw a TV programme (maybe Michael Portillo's railway programme) where the
presenter was taken into an underground tunnel somewhere, and he was told
that the only cars that were allowed underground in the tunnels were diesel
ones, because petrol engines were too likely to generate a spark that could
ignite flammable fumes,

John Williamson

2023-07-27 10:27:06 UTC

Post by tony sayer
Begs the question what do the staff at Fylingdales use for transport?,
push bikes?...

I saw a TV programme (maybe Michael Portillo's railway programme) where
the presenter was taken into an underground tunnel somewhere, and he was
told that the only cars that were allowed underground in the tunnels
were diesel ones, because petrol engines were too likely to generate a
spark that could ignite flammable fumes,

If they develop a leak, petrol is also far easier to ignite than diesel.

--
Tciao for Now!

John.

2023-07-27 10:41:38 UTC

Post by tony sayer
Begs the question what do the staff at Fylingdales use for transport?,
push bikes?...

I saw a TV programme (maybe Michael Portillo's railway programme) where
the presenter was taken into an underground tunnel somewhere, and he was
told that the only cars that were allowed underground in the tunnels
were diesel ones, because petrol engines were too likely to generate a
spark that could ignite flammable fumes,

If they develop a leak, petrol is also far easier to ignite than diesel.

Too right.

The first place I worked, as a summer job before going to university, was a
large open site with lots of grassy areas between buildings - it had been an
old airfield.

Everyone had to do fire safety testing as part of the induction process.

The fire safety guy had laid two shallow metal pans on the grass, about a
metre square and a centimetre or so deep. He poured a bit of petrol in one
of them. It was a hot sunny day so the petrol would have started to
evaporate. He lit a rag on a metal pole and brought it near the tray. The
petrol ignited when the torch was a metre or so away: the fumes ignited and
carried the ignition source back to the tray.

Once it had safely burned away, he repeated the process with diesel fuel. He
could not ignite it, even by bringing the torch so it was almost in contact
with the fuel, and as soon as he dipped it in, the flame was extinguished.

The only way he could ignite the diesel was to suck a bit up into a tube
with a narrow end, making a crude diesel injector. The tiny droplets that
emerged could be ignited with the torch, but even that didn't ignite the
rest of the fuel in the tray, just making a jet that went out as soon as the
torch was removed.

J. P. Gilliver

2023-07-27 15:06:42 UTC

Post by tony sayer
Begs the question what do the staff at Fylingdales use for transport?,
push bikes?...

(Recent almost manic coverage of e-bike fires has obviously generated
the question in my mind of why we don't hear about such with EVs - and
why no-one was even raising the _question_ with the e-bike panic. One
could almost suspect government censorship ...)

Post by J. P. Gilliver
Not the same question, but I remember hearing/seeing somewhere that at
certain oil (gas?) refinery sites, conventional vehicles were not
allowed, especially diesel ones, because the air was sufficiently
flammable that even if you turned the ignition off, the engine would
race, to the extent of flames coming out of the exhaust; vehicles for
use on the site had to be modified in some way.

I saw a TV programme (maybe Michael Portillo's railway programme) where
the presenter was taken into an underground tunnel somewhere, and he was
told that the only cars that were allowed underground in the tunnels
were diesel ones, because petrol engines were too likely to generate a
spark that could ignite flammable fumes,

Though in a flammable atmosphere, Diesel ones are more likely to run
away.

Post by John Williamson
If they develop a leak, petrol is also far easier to ignite than diesel.

Too right.

[Interesting story snipped]
I remember reading/hearing somewhere that during the war, there were
tanks with petrol engines and tanks with diesel engines (presumably
because of engine manufacturing capacity), and you were far more likely
to survive a fire in the latter. With the former known to the Germans as
"Tommy-cookers".

--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)***@T+H+Sh0!:`)DNAf

There's only so much you can do... with gravel.
- Charlie Dimmock, RT 2016/7/9-15

2023-07-27 11:13:20 UTC

Post by NY
I saw a TV programme (maybe Michael Portillo's railway programme) where the
presenter was taken into an underground tunnel somewhere, and he was told
that the only cars that were allowed underground in the tunnels were diesel
ones, because petrol engines were too likely to generate a spark that could
ignite flammable fumes,

That is quite common.

We had a contract at an underground power station which involved a drive
down a tunnel. Petrol vehicles were not allowed and any combustibles in
the vehicle had to be declared.

All vehicles were parked facing outwards with keys inside.

There was a tally board and in the event of an alarm you would be put in
vehicles and taken out. In the event of a high level alarm, you could
use any vehicle and GET OUT!

It would be interesting to know if battery vehicles are allowed, I was
told a few days ago of another one exploding and it being hushed up.

John Williamson

2023-07-27 13:15:19 UTC

Post by MB
It would be interesting to know if battery vehicles are allowed, I was
told a few days ago of another one exploding and it being hushed up.

There is a ship carrying a number which was on fire near Amsterdam
recently (Yesterday?) and one crew member was killed while trying to put
the fire out,

--
Tciao for Now!

John.

J. P. Gilliver

2023-07-27 15:12:52 UTC

I think that would be Dinorwic (or is it -wig?) pumped storage plant in
a Welsh mountain - used for peak levelling; it pumps water from the
reservoir at the bottom to the one at the top when there is spare
capacity on the grid, and the pumps can be switched to generators at
times of peak demand, letting the water fall back down again to drive
them. They're quite proud of how few seconds the whole thing can be
reversed if unexpectedly needed. But should something break, the
chambers inside the mountain would fill with water _very_ fast, hence
the need for a swift escape.

Post by MB
There was a tally board and in the event of an alarm you would be put
in vehicles and taken out. In the event of a high level alarm, you
could use any vehicle and GET OUT!
It would be interesting to know if battery vehicles are allowed, I was
told a few days ago of another one exploding and it being hushed up.

--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)***@T+H+Sh0!:`)DNAf

There's only so much you can do... with gravel.
- Charlie Dimmock, RT 2016/7/9-15

2023-07-27 18:38:54 UTC

Post by J. P. Gilliver
I think that would be Dinorwic (or is it -wig?) pumped storage plant in
a Welsh mountain

No, more local.

If you go on the tour then just hope you do not have to use the
emergency exit! :-)

2023-07-27 18:40:39 UTC

Post by J. P. Gilliver
But should something break, the
chambers inside the mountain would fill with water_very_ fast, hence
the need for a swift escape.

We were told that someone had worked out how quickly it would fill with
water is a pipe failed (they are *BIG* pipes!).

There would be no hope of escape, it would fill much too fast.

Woody

2023-07-27 21:10:47 UTC

Post by J. P. Gilliver
But should something break, the
chambers inside the mountain would fill with water_very_ fast, hence
the need for a swift escape.

We were told that someone had worked out how quickly it would fill with
water is a pipe failed (they are *BIG* pipes!).
There would be no hope of escape, it would fill much too fast.

In theory if all six units were spinning on air (as they would be just
before the adverts in the latest James Bond film being shown on TV and a
cuppa would be needed) they could go from 0 to 1320MW in 10.4 seconds.
Conversely a demand stop would take them from 1320MW to zero in a little
over 4 seconds BUT the catch pond (about the size of the old Wembley
Stadium) at the top of the main 525ft drop shaft would fill in less than
10 seconds from a shaft of water 30m across and theoretically over 50m
high - but I don't think they ever tried it. The pipes feeding the units
were 2m diameter with a valve like a perforated golf ball. At full gen
the water would run through those valves at something over 1000psi and
85000 gallons a second.

The best bit? It was designed to run on demand for typically about 15-30
minutes (maximum to drain Marchlyn Mawr - the header tank if you like -
was reckoned to be about 90 mins) whilst gas turbines (around 4 minutes)
or nuclear (about 10 minutes) came on line. The place was costed to
build as (IMSMC) about £40m - it actually cost £484m! However when they
started using it they found it was so efficient they could let it run
for most of the load shedding period. Doing so it cost something like 20
months to pay for itself!!!

If you have a look at Google sky view and follow the entry road you will
see the south facing entrance tunnel (green spot on it). Then zoom out
scan away NE to find Marchlyn Mawr. If you take a diagonal line SW from
MM and zoom in a bit you will eventually see the surge pond - long oval
with the circular surge shaft in the centre - and if you zoom in a bit
more following the same line you will see another circular object which
has a grille on the top. If the station flooded there was a vertical
ladder underneath this last object, the top of which was about 30ft
below the grille but the platform atop the ladder would have been about
6ft above the highest water level!

They generate at 11KV and about 18500A but there is a 275KV sub-station
inside the mountain which takes the power away in water-cooled pipes
about 9 miles before going overhead. The whole place can be controlled
locally by three shift staff, or remotely from Connah's Quay on Deeside.

It is now known as 'Electric Mountain.' A TV (slightly
anti-nuclear/Thatcher) drama called Edge of Darkness starring Bob Peck
had large sections (allegedly Aldermaston) filmed inside Dinorwic in
1985. It was repeated (for the first time?) earlier this year.

J. P. Gilliver

2023-07-28 02:59:24 UTC

Post by Woody

Post by J. P. Gilliver
But should something break, the
chambers inside the mountain would fill with water_very_ fast, hence
the need for a swift escape.

We were told that someone had worked out how quickly it would fill
with water is a pipe failed (they are *BIG* pipes!).
There would be no hope of escape, it would fill much too fast.

[]

Post by Woody
They generate at 11KV and about 18500A but there is a 275KV sub-station
inside the mountain which takes the power away in water-cooled pipes
about 9 miles before going overhead. The whole place can be controlled
locally by three shift staff, or remotely from Connah's Quay on Deeside.

It kept - or at least helped - the company I worked for briefly (about
1979-'82 I think), Reyrolle Switchgear, in business for some years.

Post by Woody
It is now known as 'Electric Mountain.' A TV (slightly
anti-nuclear/Thatcher) drama called Edge of Darkness starring Bob Peck
had large sections (allegedly Aldermaston) filmed inside Dinorwic in
1985. It was repeated (for the first time?) earlier this year.

Is it open to the public? Sounds like it'd be quite interesting to visit
(for those of us of an engineering bent).

--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)***@T+H+Sh0!:`)DNAf

"If even one person" arguments allow the perfect to become the enemy of the
good, and thus they tend to cause more harm than good.
- Jimmy Akins quoted by Scott Adams, 2015-5-5

2023-07-28 06:28:31 UTC

Post by J. P. Gilliver
Is it open to the public? Sounds like it'd be quite interesting to visit
(for those of us of an engineering bent).

Cruachan has a visitor centre with exhibition and cafe - with Pine
Martens regularly seen outside eating scraps.

You can then be taken to a viewing gallery at the end of the tunnel
where you can see the generators. We got to into the generator hall and
control room - fortunately none were running so it was quiet!

You used to be able to borrow the gate key to drive up to the dam but
too many people did not return the kay so they stopped that. We had a
key for access to a site up there so got to drive over the dam.

charles

2023-07-28 08:15:02 UTC

Post by J. P. Gilliver
Is it open to the public? Sounds like it'd be quite interesting to visit
(for those of us of an engineering bent).

Cruachan has a visitor centre with exhibition and cafe - with Pine
Martens regularly seen outside eating scraps.
You can then be taken to a viewing gallery at the end of the tunnel
where you can see the generators. We got to into the generator hall and
control room - fortunately none were running so it was quiet!
You used to be able to borrow the gate key to drive up to the dam but
too many people did not return the kay so they stopped that. We had a
key for access to a site up there so got to drive over the dam.

Just after the Torosay transmitter came on air I was in the area
carryingout a survey and I stopped at Cruachan, which was new. I got a
look round - free.

--
from KT24 in Surrey, England - sent from my RISC OS 4té
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

2023-07-28 09:36:38 UTC

Post by charles
Just after the Torosay transmitter came on air I was in the area
carryingout a survey and I stopped at Cruachan, which was new. I got a
look round - free.

It can be a handy place for a coffee in the cafe because not much along
there.

charles

2023-07-28 10:00:02 UTC

Post by charles
Just after the Torosay transmitter came on air I was in the area
carryingout a survey and I stopped at Cruachan, which was new. I got a
look round - free.

It can be a handy place for a coffee in the cafe because not much along
there.

Indeed so. I was only a few miles away (Dalmally) last month

--
from KT24 in Surrey, England - sent from my RISC OS 4té
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

John Williamson

2023-07-27 16:57:33 UTC

Post by MB
It would be interesting to know if battery vehicles are allowed, I was
told a few days ago of another one exploding and it being hushed up.

Many hybrid vehicles use the same battery technology. About once a week
I see a story of yet another bus igniting and the batteries exploding.
It closes the road for a while, and it gets resurfaced overnight.

I have personally seen it happen to a car on the M62, and every minute
or so, another battery would go pop with the resulting ball of hot gas.
That carriageway was closed for an hour or two, when I went past in the
way back, there was a melted patch, and the following morning, there was
a patch of fresh tarmac on the hard shoulder.

The fire brigades in the UK, and, presumably elsewhere, now have
approved procedures for dealing with the problem.

--
Tciao for Now!

John.

Liz Tuddenham

2023-07-27 15:18:24 UTC

Post by tony sayer
Begs the question what do the staff at Fylingdales use for transport?,
push bikes?...

Whilst Diesel is inherently safer than petrol in most circumstances,
diesel engines can run away uncontrollably if they suck fuel into the
air inlet. A failed oil seal in the turbo is the most likely cause and
the results can be frightening.

Boats with propane cooking arrangements are a particular risk because
the propane collects in the bilges and a runaway engine can tear a hole
in the bottom if it seizes when overspeeding. I believe it is mandatory
to have speed-operated strangler valves in the air intakes of all diesel
engines in seagoing boats.

--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

Liz Tuddenham

2023-07-26 18:48:09 UTC

Post by tony sayer
scribeth thus

I asked at Fylingdales what frequency it operated on and was told it was
secret! Obviously never heard of scanners or spectrum analysers.
With those levels of RF, the frequency is probably irrelevant with most
receivers.
There used to be remote car keys operating on a lot of different
frequencies (one of our vehicles at work had an illegal one!). But
probably not a problem now that most are factory fitted.

The real problem is those cars that have no mechanical keyhole (or else one
that needs tools to access in an emergency), where you can only use the
remote. I'm used to one of my car keys (I keep it as the spare) not
operating the central locking (yes I've replaced its battery!) and so having
to lock/unlock the doors the old-fashioned way when Ii take the car to the
garage to be serviced. And I warn them, though I imagine they are used to
central locking failing for whatever reason and know how to use the key
blade.
And if the RF is so strong that it even affects the key-ECU comms for the
immobiliser, then you are totally stuffed. I presume the only way around
that is to tow the car far enough away that the key and immobiliser can talk
and so negotiate to enable the engine.

Begs the question what do the staff at Fylingdales use for transport?,
push bikes?...

Good job they don't transmit on wavelengths around 2 metres, a half-wave
pushbike frame could give you some nasty R.F. burns.

--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

J. P. Gilliver

2023-07-22 15:05:17 UTC

In message <***@brightview.co.uk> at Sat,
22 Jul 2023 15:18:44, NY <***@privacy.net> writes
[]

Post by NY
The ultimate *visible* RFI was on the news reports from the warships in
the Falklands War. To begin with, the reports were always preceded by
an apology for the poor picture quality - because the ship's rotating
radar pulse stomped a great big noise bar over the picture every couple
of seconds. Of course film would have been immune but there would have
been the "little" problem of taking a film-processing system and
telecine ;-)
ENG cameras have to be immune to all *normal* RFI, but immunity from a
megawatt of SHF from a radar wouldn't have been tested for ;-)
Don't know whether it affected the electronics as such (amplifiers etc)
or whether it buggered up the electron beams inside the plumbicon tubes
- because the early 80s were almost certainly before solid-state sensors.

I always assumed it got into the electronics, rather than directly
affecting the light sensor(s) [of whatever sort].

It did occur to me that the patterning might be giving away the
structure of the radar pulses - they obviously weren't just a type A
radar, but a digitally-complex pulse - to anyone seeing it, but
presumably either this wasn't thought of, it was thought to be not
important, or the structure was ever-changing and such analysis was
pointless.

--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)***@T+H+Sh0!:`)DNAf

Speed has never killed anyone. Suddenly becoming stationary, that's what gets
you. - Jeremy Clarkson, Top Gear

Brian Gaff

2023-07-23 10:11:13 UTC

A lot of the complexity on ships radar is to use something called Clearscan,
a method of removing clutter, ie reflections from waves. The characteristic
of such returns was different according to the pulse width and hence some
clever real time processing could make a decision which was clutter by
comparing the returns. I think that due to the fact waves move the relative
position will move on different pulses, but you need to know which pulse is
which hence the time domain changes you see.
Brian
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Blind user, so no pictures please
Note this Signature is meaningless.!

Post by NY
The ultimate *visible* RFI was on the news reports from the warships in
the Falklands War. To begin with, the reports were always preceded by an
apology for the poor picture quality - because the ship's rotating radar
pulse stomped a great big noise bar over the picture every couple of
seconds. Of course film would have been immune but there would have been
the "little" problem of taking a film-processing system and telecine ;-)
ENG cameras have to be immune to all *normal* RFI, but immunity from a
megawatt of SHF from a radar wouldn't have been tested for ;-)
Don't know whether it affected the electronics as such (amplifiers etc) or
whether it buggered up the electron beams inside the plumbicon tubes -
because the early 80s were almost certainly before solid-state sensors.

I always assumed it got into the electronics, rather than directly
affecting the light sensor(s) [of whatever sort].
It did occur to me that the patterning might be giving away the structure
of the radar pulses - they obviously weren't just a type A radar, but a
digitally-complex pulse - to anyone seeing it, but presumably either this
wasn't thought of, it was thought to be not important, or the structure
was ever-changing and such analysis was pointless.
--
Speed has never killed anyone. Suddenly becoming stationary, that's what gets
you. - Jeremy Clarkson, Top Gear

tony sayer

2023-07-22 15:09:46 UTC

The ultimate *visible* RFI was on the news reports from the warships in
the Falklands War. To begin with, the reports were always preceded by an
apology for the poor picture quality - because the ship's rotating radar
pulse stomped a great big noise bar over the picture every couple of
seconds. Of course film would have been immune but there would have been
the "little" problem of taking a film-processing system and telecine ;-)
ENG cameras have to be immune to all *normal* RFI, but immunity from a
megawatt of SHF from a radar wouldn't have been tested for ;-)
Don't know whether it affected the electronics as such (amplifiers etc)
or whether it buggered up the electron beams inside the plumbicon tubes
- because the early 80s were almost certainly before solid-state sensors.

Wasn't their a tale of some incoming missile not being spotted as a
radar was tuned off whilst communicating with London?..

--
Tony Sayer

Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.

Brian Gaff

2023-07-23 10:21:11 UTC

I don't know about that, but normally there is another radar in use which is
more accurate at finding fast moving missiles. Indeed around that time a
system called Sea possum was being trialed that married up a special radar
with a Gattling gun capable of firing insane amounts of rounds. I guess the
idea was to so damage the missile as to render it useless.
They tried to sell a similar system for land warfare but nobody bought it.
I was not party as to why, but I'd guess it was its lack of successin
downing missiles very low down and coming head on. You have to remember that
most of those missiles are designed to Pearce armour before exploding within
the target to cause maximum damage with a small explosive. Its a bit like
the Rapier missile which was really a hitile as it was designed to pierce
the aircraft, then explode, most missiles merely used Shrapnel grenade
technology to hope the exploding bits would damage the aircraft.
Brian
--
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Blind user, so no pictures please
Note this Signature is meaningless.!

The ultimate *visible* RFI was on the news reports from the warships in
the Falklands War. To begin with, the reports were always preceded by an
apology for the poor picture quality - because the ship's rotating radar
pulse stomped a great big noise bar over the picture every couple of
seconds. Of course film would have been immune but there would have been
the "little" problem of taking a film-processing system and telecine ;-)
ENG cameras have to be immune to all *normal* RFI, but immunity from a
megawatt of SHF from a radar wouldn't have been tested for ;-)
Don't know whether it affected the electronics as such (amplifiers etc)
or whether it buggered up the electron beams inside the plumbicon tubes
- because the early 80s were almost certainly before solid-state sensors.

Wasn't their a tale of some incoming missile not being spotted as a
radar was tuned off whilst communicating with London?..
--
Tony Sayer
Man is least himself when he talks in his own person.
Give him a keyboard, and he will reveal himself.

2023-07-22 15:39:21 UTC

Many years ago there was a live OB of a climb on Ben Nevis, they used
our team base as their base with a large scanner in the car park and a
large comms vehicle. A small OB vehicle with sound, vision etc in one
vehicle was parked nearby and an experimental trailer mounted satellite
terminal.

It all very interesting and we got a couple of meals from the location
catering people.

They put a camera near for general views of Ben Nevis but had loads of
intereference from our Band I transmitter. They could not understand
this because they test everything at Brookmans Park and Crystal Palace.
We explained that BP andCP might run a lot more power but the antenna
are much higher, our Band I antenna was about 90 ft agl.

So we told them to let us know when they were going to use that camera
and we would reducepower, we actually knocked off the amplifiers briefly.

When they had finished they said they were very grateful for the help.
We told them to put the word around to not going around thanking anyone
senior as it might go down very well.

We did not have BBC2 locally at that time so they said they would fix
something up for us. A bit later one of their riggers brought a studio
quality monitor into our workshop with several drums of cable. We asked
why so many - they had given us a main and reserve feed!

Mark Carver

2023-07-25 07:47:16 UTC

Post by MB
They put a camera near for general views of Ben Nevis but had loads of
intereference from our Band I transmitter.

When HTV built their new studio centre at Culverhouse Cross in 1984, it
was only a mile or so from Wenvoe. The RF levels from Wenvoe's Band I
transmitter on the site were were so high, they had to build the
technical areas in Faraday Cages. Of course, Band I TV ceased in
January 1985, so it wasn't required for very long.

charles

2023-07-25 09:15:02 UTC

Post by Mark Carver

Post by MB
They put a camera near for general views of Ben Nevis but had loads of
intereference from our Band I transmitter.

at BBC TV Centre, if you connected a set of headphones across the ststion
50v battery, you couuld hear The Light Programme from Brookmans Park.

--
from KT24 in Surrey, England - sent from my RISC OS 4té
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

The Other John

2023-07-25 09:38:15 UTC

Post by charles
at BBC TV Centre, if you connected a set of headphones across the
ststion 50v battery, you couuld hear The Light Programme from Brookmans
Park.

When I was in Vision Control ('racks') at ATV's Wood Green Empire a mate
in the sound department said 'come and listen to this'. He faded up a
channel on the mixer and said 'can you hear it?'. I said 'no, what can you
hear?' and he said 'morse code on 16kHz from Rugby'.

--
TOJ.

Liz Tuddenham

2023-07-25 15:14:55 UTC

charles <***@candehope.me.uk> wrote:

[...]

Post by charles
at BBC TV Centre, if you connected a set of headphones across the ststion
50v battery, you couuld hear The Light Programme from Brookmans Park.

Only for a few seconds, I suppose - then your ears began to cook.

50v across 600 ohms = 4 watts.

--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

charles

2023-07-25 16:00:02 UTC

Post by charles
at BBC TV Centre, if you connected a set of headphones across the ststion
50v battery, you couuld hear The Light Programme from Brookmans Park.

Only for a few seconds, I suppose - then your ears began to cook.
50v across 600 ohms = 4 watts.

but, if you had a capacitor in the path, there'd be no DC flow.

--
from KT24 in Surrey, England - sent from my RISC OS 4té
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

Liz Tuddenham

2023-07-25 17:56:06 UTC

Post by charles
at BBC TV Centre, if you connected a set of headphones across the ststion
50v battery, you couuld hear The Light Programme from Brookmans Park.

Only for a few seconds, I suppose - then your ears began to cook.
50v across 600 ohms = 4 watts.

but, if you had a capacitor in the path, there'd be no DC flow.

Nobody mentioned one.

--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

charles

2023-07-25 18:30:02 UTC

Post by charles
at BBC TV Centre, if you connected a set of headphones across the ststion
50v battery, you couuld hear The Light Programme from Brookmans Park.

Only for a few seconds, I suppose - then your ears began to cook.
50v across 600 ohms = 4 watts.

but, if you had a capacitor in the path, there'd be no DC flow.

Nobody mentioned one.

True, but who'd be silly enough to put a set of cans directly across a 50v
battery

--
from KT24 in Surrey, England - sent from my RISC OS 4té
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

Max Demian

2023-07-25 18:35:50 UTC

Post by charles
at BBC TV Centre, if you connected a set of headphones across the ststion
50v battery, you couuld hear The Light Programme from Brookmans Park.

Only for a few seconds, I suppose - then your ears began to cook.
50v across 600 ohms = 4 watts.

but, if you had a capacitor in the path, there'd be no DC flow.

Nobody mentioned one.

True, but who'd be silly enough to put a set of cans directly across a 50v
battery

I don't see the problem if they are high impedance.

--
Max Demian

John Williamson

2023-07-25 18:42:19 UTC

Post by Max Demian

Post by charles
True, but who'd be silly enough to put a set of cans directly across a 50v
battery

I don't see the problem if they are high impedance.

Piezo phones might work, as they are pretty much open circuit at DC, but
any magnetic drive type would have the transducers stuck fast at one end
of their travel by the DC.

--
Tciao for Now!

John.

Liz Tuddenham

2023-07-25 19:18:11 UTC

Post by Max Demian

Post by charles
at BBC TV Centre, if you connected a set of headphones across the
ststion 50v battery, you couuld hear The Light Programme from
Brookmans Park.

Only for a few seconds, I suppose - then your ears began to cook.
50v across 600 ohms = 4 watts.

but, if you had a capacitor in the path, there'd be no DC flow.

Nobody mentioned one.

True, but who'd be silly enough to put a set of cans directly across a 50v
battery

I don't see the problem if they are high impedance.

" at BBC TV Centre, if you connected a set of headphones across ..."

By then I would have thought most of the BBC headphones were the 600-ohm
STC type.

--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

Liz Tuddenham

2023-07-25 19:18:11 UTC

Post by charles
at BBC TV Centre, if you connected a set of headphones across the
ststion 50v battery, you couuld hear The Light Programme from
Brookmans Park.

Only for a few seconds, I suppose - then your ears began to cook.
50v across 600 ohms = 4 watts.

but, if you had a capacitor in the path, there'd be no DC flow.

Nobody mentioned one.

True, but who'd be silly enough to put a set of cans directly across a 50v
battery

Well, it lookd as though that was what you were suggesting. :-)

--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

2023-07-26 06:54:17 UTC

Post by charles
at BBC TV Centre, if you connected a set of headphones across the ststion
50v battery, you couuld hear The Light Programme from Brookmans Park.

At Criggion you could 'hear' the transmissions inside the coil room
without any receiver or headphones!

2023-07-26 06:47:08 UTC

Post by Mark Carver
When HTV built their new studio centre at Culverhouse Cross in 1984, it
was only a mile or so from Wenvoe. The RF levels from Wenvoe's Band I
transmitter on the site were were so high, they had to build the
technical areas in Faraday Cages. Of course, Band I TV ceased in
January 1985, so it wasn't required for very long.

I was told some time ago that Marks and Spencers had to spend a lot on
protecting their store near Lisnagarvey from the effects of RF.

Liz Tuddenham

2023-07-26 09:02:28 UTC

I was told some time ago that Marks and Spencers had to spend a lot on
protecting their store near Lisnagarvey from the effects of RF.

What is the legal situation if equipment in an existing building is
affected by a newly-built transmitter?

A long time ago (when I had a G8 licence) my station was 'raided' by a
P.O. Wireless Inspector. There had been complaints from a neighbour
about interference on his rented T.V. My transmitter was within spec.
and his set was missing some screening, so in that particular case the
problem was his.

If I had been a broadcaster putting out a huge, but legal, signal and
nearby buildings were saturated, would I be legally responsible for
mitigating the nuisance?

--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

2023-07-26 09:44:46 UTC

Post by Liz Tuddenham
If I had been a broadcaster putting out a huge, but legal, signal and
nearby buildings were saturated, would I be legally responsible for
mitigating the nuisance?

Sure someone knows better but I think on shared transmitter sites then
it is the responsibility of the last person to go on the site to provide
filtering.

So I think that if you decide to use a site and your own equipment
cannot cope with quite legal clean transmissions then it is your own
problem.

Though if it is because of a transmitter producing out of band
interference then it would be probably be their responsibility to make
their transmitter comply with regulations first.

Mark Carver

2023-07-26 14:17:21 UTC

Post by Liz Tuddenham
What is the legal situation if equipment in an existing building is
affected by a newly-built transmitter?
There's this little story from the era the BBC had an AM transmitter sited at Sutton Coldfield

http://txfeatures.mb21.co.uk/coldfield/11.shtml

The Other John

2023-07-22 19:00:15 UTC

Sometime around the late '60s or early 70s I was recording on 2" quad VTR
for ABC of America the arrival of Richard Nixon at Heathrow from a feed of
a BBC OB unit, but as Air Force One came in to land it's anti-missile
defence electronics completely wiped out the Beeb's microwave link and we
lost the picture.

--
TOJ.

charles

2023-07-22 19:45:02 UTC

Post by The Other John

Sometime around the late '60s or early 70s I was recording on 2" quad VTR
for ABC of America the arrival of Richard Nixon at Heathrow from a feed
of a BBC OB unit, but as Air Force One came in to land it's anti-missile
defence electronics completely wiped out the Beeb's microwave link and
we lost the picture.

--
from KT24 in Surrey, England - sent from my RISC OS 4té
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

Brian Gaff

2023-07-23 10:29:45 UTC

Yes well nowadays you would not get away with this, but some of the Russian
space communication some years ago was in the middle of band 3. You could
when in range, clearly hear them talking and joking in mostly Russian but
some English.
Brian
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Blind user, so no pictures please
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Post by The Other John

Sometime around the late '60s or early 70s I was recording on 2" quad VTR
for ABC of America the arrival of Richard Nixon at Heathrow from a feed
of a BBC OB unit, but as Air Force One came in to land it's anti-missile
defence electronics completely wiped out the Beeb's microwave link and
we lost the picture.

I managed to avoid a RFI problem whm in the early '90s the Russian leader
was due to visit Chequers to meet our PM. The uplink frequency the
Russians wanted to use was slap in the middle of BBC 2 from Oxford - so I
said "no".
--
from KT24 in Surrey, England - sent from my RISC OS 4té
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

Brian Gregory

2023-07-28 01:38:48 UTC

On 23/07/2023 11:29, Brian Gaff wrote:
192MHz was a Russian space comms frequency.
I remember a long time ago hearing very occasional weak Russian sounding
stuff on 143.625MHz.

Post by Brian Gaff
Yes well nowadays you would not get away with this, but some of the Russian
space communication some years ago was in the middle of band 3. You could
when in range, clearly hear them talking and joking in mostly Russian but
some English.
Brian

--
Brian Gregory (in England).

Brian Gregory

2023-07-29 14:47:48 UTC

Sorry. Just noticed I messed up the quoting on that.

--
Brian Gregory (in England).

wrightsaerials@aol.com

2023-07-25 01:00:35 UTC

Post by charles
I managed to avoid a RFI problem whm in the early '90s the Russian leader
was due to visit Chequers to meet our PM. The uplink frequency the
Russians wanted to use was slap in the middle of BBC 2 from Oxford - so I
said "no".
--
from KT24 in Surrey, England - sent from my RISC OS 4té

During either the World Student Games or the Special Olympics at Sheffield (I can't remember which) the BBC OB outfit had some sort of intercom that worked on the same frequency as BBC1 from Crosspool.

Bill

Roderick Stewart

2023-07-25 08:39:12 UTC

Post by ***@aol.com

Many years ago when I lived in Putney, the cluster of vehicles the BBC
set up for the boat race was by the river at the end of our road.
Their talkback channel was FM, if I remember correctly at about
92.5MHz, but certainly in the middle of the broadcast band.

I didn't listen to much of it though, as it was too much like being at
work.

Rod.

charles

2023-07-25 09:30:01 UTC

Post by Roderick Stewart

Post by ***@aol.com

Post by charles
I managed to avoid a RFI problem whm in the early '90s the Russian
leader was due to visit Chequers to meet our PM. The uplink frequency
the Russians wanted to use was slap in the middle of BBC 2 from
Oxford - so I said "no". -- from KT24 in Surrey, England - sent from
my RISC OS 4té

During either the World Student Games or the Special Olympics at
Sheffield (I can't remember which) the BBC OB outfit had some sort of
intercom that worked on the same frequency as BBC1 from Crosspool.
Bill

Many years ago when I lived in Putney, the cluster of vehicles the BBC
set up for the boat race was by the river at the end of our road. Their
talkback channel was FM, if I remember correctly at about 92.5MHz, but
certainly in the middle of the broadcast band.
I didn't listen to much of it though, as it was too much like being at
work.
Rod.

I remember hearing ITV talkback from Epsom racecourse on the FM band
(1970s). The bit I remember was "Brian, zoom in a bit" "Please use proper
camera designations, there are 3 cameramen called Brian today."

--
from KT24 in Surrey, England - sent from my RISC OS 4té
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

Liz Tuddenham

2023-07-25 15:14:55 UTC

Post by Roderick Stewart

Post by ***@aol.com

During either the World Student Games or the Special Olympics at
Sheffield (I can't remember which) the BBC OB outfit had some sort of
intercom that worked on the same frequency as BBC1 from Crosspool.
Bill

Many years ago when I lived in Putney, the cluster of vehicles the BBC
set up for the boat race was by the river at the end of our road.
Their talkback channel was FM, if I remember correctly at about
92.5MHz, but certainly in the middle of the broadcast band.
I didn't listen to much of it though, as it was too much like being at
work.

There used to be studio talkback on narrow-band FM from the Mendip
transmitter mast, presumably for the benefit of roving OB units. It was
entertaining listening to the rehearsals for the evening local
television news - especially when a lady announcer's mic became
unclipped and it had to be retrieved.

I seem to remember the transmission was around 175 Mc/s, but I may be
mistaken.

--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

Brian Gregory

2023-07-28 01:42:52 UTC

Post by Liz Tuddenham
There used to be studio talkback on narrow-band FM from the Mendip
transmitter mast, presumably for the benefit of roving OB units. It was
entertaining listening to the rehearsals for the evening local
television news - especially when a lady announcer's mic became
unclipped and it had to be retrieved.
I seem to remember the transmission was around 175 Mc/s, but I may be
mistaken.

When on the South coast or Isle of Wight we could sometimes hear the
same kind of thing for BBC South on, if I remember correctly exactly 141MHz.

--
Brian Gregory (in England).

2023-07-28 06:32:33 UTC

Post by Brian Gregory
When on the South coast or Isle of Wight we could sometimes hear the
same kind of thing for BBC South on, if I remember correctly exactly 141MHz.

Transmitter Group had a channel on 141 and think possibly other people,
mainly OBs.

I have a photograph that I took during the Investiture of Charlie, OBs
had a big group of RTs including a channel that was kept in reserve so
the nationalists would not know it and so be able to monitor / jam.

Paul Ratcliffe

2023-07-29 00:08:15 UTC

On Tue, 25 Jul 2023 16:14:55 +0100, Liz Tuddenham

Post by Liz Tuddenham
There used to be studio talkback on narrow-band FM from the Mendip
transmitter mast, presumably for the benefit of roving OB units.

Yes, that was ours.

Post by Liz Tuddenham
It was entertaining listening to the rehearsals for the evening local
television news - especially when a lady announcer's mic became
unclipped and it had to be retrieved.

Was it?

Post by Liz Tuddenham
I seem to remember the transmission was around 175 Mc/s, but I may be
mistaken.

Ch 1 on 141.375 MHz was the one from Mendip. I can't remember the
exact frequency of Ch 2 which was used from other locations, but it was
in the same ball-park.

Liz Tuddenham

2023-07-29 13:39:02 UTC

Post by Paul Ratcliffe
On Tue, 25 Jul 2023 16:14:55 +0100, Liz Tuddenham

Post by Liz Tuddenham
There used to be studio talkback on narrow-band FM from the Mendip
transmitter mast, presumably for the benefit of roving OB units.

Yes, that was ours.

You had an unofficial fan club.

Post by Paul Ratcliffe

Post by Liz Tuddenham
It was entertaining listening to the rehearsals for the evening local
television news - especially when a lady announcer's mic became
unclipped and it had to be retrieved.

Was it?

She retrived it herself despite the gallant offers of help from a
co-presenter.

Post by Paul Ratcliffe

Post by Liz Tuddenham
I seem to remember the transmission was around 175 Mc/s, but I may be
mistaken.

Ch 1 on 141.375 MHz was the one from Mendip. I can't remember the
exact frequency of Ch 2 which was used from other locations, but it was
in the same ball-park.

Thanks, I wasn't sure about that.

--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

Paul Ratcliffe

2023-10-07 11:53:27 UTC

On Sat, 29 Jul 2023 14:39:02 +0100, Liz Tuddenham

Post by Paul Ratcliffe
Ch 1 on 141.375 MHz was the one from Mendip. I can't remember the
exact frequency of Ch 2 which was used from other locations, but it was
in the same ball-park.

Thanks, I wasn't sure about that.

I've found it during a clear out - 141.4625 MHz.
I believe we still pay the licence for that, but it is hardly used
and there was talk of ceasing it.

Local radio (round here anyway) used to use 141.24375, .30625 and .25635
but they are long gone.

2023-07-29 15:13:12 UTC

Ch 1 on 141.375 MHz was the one from Mendip. I can't remember the exact
frequency of Ch 2 which was used from other locations, but it was in the
same ball-park.

Could it have been that the mobile channels were around 141 MHz and 170
MHz was used for linking back to the base?

Woody

2023-07-29 15:52:55 UTC

Post by Paul Ratcliffe
Ch 1 on 141.375 MHz was the one from Mendip. I can't remember the
exact frequency of Ch 2 which was used from other locations, but it
was in the same ball-park.

Could it have been that the mobile channels were around 141 MHz and 170
MHz was used for linking back to the base?

IMSMC the long range radio mics as used at, for example, the Grand
National, were around 140-141MHz as noted. Some frequencies in Band IV
and later Band V were also used. Studio radio mics were mostly about
174MHz but when Band IV became available for mobile radio and data they
were shifted onto TV channel 69 (about 860MHz) where they remain to this
day (I think). Interesting that the UK UHF band was 21-69 but whilst 21
was used (used even more now with DTTV) 69 was never allocated.

Mark Carver

2023-07-31 08:48:50 UTC

Post by Woody

Post by Paul Ratcliffe
Ch 1 on 141.375 MHz was the one from Mendip. I can't remember the
exact frequency of Ch 2 which was used from other locations, but it
was in the same ball-park.

Could it have been that the mobile channels were around 141 MHz and
170 MHz was used for linking back to the base?

IMSMC the long range radio mics as used at, for example, the Grand
National, were around 140-141MHz as noted. Some frequencies in Band IV
and later Band V were also used. Studio radio mics were mostly about
174MHz but when Band IV became available for mobile radio and data
they were shifted onto TV channel 69 (about 860MHz) where they remain
to this day (I think). Interesting that the UK UHF band was 21-69 but
whilst 21 was used (used even more now with DTTV) 69 was never allocated.

The 141 MHz Rx/Tx at Mendip under discussion was radio talkback, (to
allow off air comms between the studio, and the director and presenters
on site at the OB, nothing to do with radio mics. A presenter will often
wear two devices, radio talkback (normally for them rx only to hear the
director etc) and radio mic, tx only (for their voice to be heard on
air, and obviously inside the truck, and back at the studio) All that
said, the body worn talkback kit will be low power, and only Rx'ing from
the OB Truck. The radio talkback to and from the studio (via Mendip in
this case) was/still is a different higher power device, using dipoles
or a yagi on the roof of the truck.

2023-07-31 13:34:05 UTC

Post by Mark Carver
The 141 MHz Rx/Tx at Mendip under discussion was radio talkback, (to
allow off air comms between the studio, and the director and presenters
on site at the OB, nothing to do with radio mics. A presenter will often
wear two devices, radio talkback (normally for them rx only to hear the
director etc) and radio mic, tx only (for their voice to be heard on
air, and obviously inside the truck, and back at the studio) All that
said, the body worn talkback kit will be low power, and only Rx'ing from
the OB Truck. The radio talkback to and from the studio (via Mendip in
this case) was/still is a different higher power device, using dipoles
or a yagi on the roof of the truck.

Just seemed a possibility, we had a 141 MHz base station liked to a 47
MHz base station with talkthrough. Worked very well with good range at
least when there were no East European fishing boats coming through on
Sporadic E :-)

Brian Gaff

2023-07-23 10:26:50 UTC

Yes, not surprising really. When we had a recruitment day where I worked
they let the children play with a live Rapier missile system obviously with
non live missiles, but the radar tracking and acquisition worked. On that
day, due to the wind changing the approach to Heathrow was over us, and a
day or so after this event a rather nasty reprimand came through saying at
least two El All flights had detected unknown radars tracking them, so one
has to be very careful who you let loos on live radar missile batteries.
Brian
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Post by The Other John

Roderick Stewart

2023-07-23 07:31:12 UTC

Post by NY
The ultimate *visible* RFI was on the news reports from the warships in
the Falklands War. To begin with, the reports were always preceded by an
apology for the poor picture quality - because the ship's rotating radar
pulse stomped a great big noise bar over the picture every couple of
seconds. Of course film would have been immune but there would have been
the "little" problem of taking a film-processing system and telecine ;-)
ENG cameras have to be immune to all *normal* RFI, but immunity from a
megawatt of SHF from a radar wouldn't have been tested for ;-)
Don't know whether it affected the electronics as such (amplifiers etc)
or whether it buggered up the electron beams inside the plumbicon tubes
- because the early 80s were almost certainly before solid-state sensors.

The head amplifiers in tube cameras had extremely high input
impedance, and picked up the signal directly from a contact ring at
the front of the tube, so that it wasn't necessary to have wires going
through the tube to the pins at the base where they might pick up
interference from the other connections. Even the usual x10
oscilloscope probe wasn't good enough to monitor signals there without
affecting them, and a x100 probe would still require slight adjustment
of the readings. One Marconi camera I worked with even had a buffer
amplifier for a test point built into the head amplifier to alleviate
this problem.

The wire between the tube and the head amplifier was as short as
possible and the whole area thoroughly screened, but my guess is that
this is where any RF interference would be most likely to intrude.

Rod.

Brian Gaff

2023-07-23 10:05:02 UTC

It was picked up by the electronics, as I worked in a radar factory, and the
video recorders of that time were very prone to this kind of thing directly
on the video stream from a test generator.

There were certain places where it was bad in the building, as all that was
between you and the aerial was a couple of panes of glass. I often wondered
how much high energy microwave we all ended up with if we used the rear
stairs and crossed the beam of the vehicle with the test device running on
it. Certainly it got into my Walkman if I had it on during the lunchbreaks.
Brian
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The ultimate *visible* RFI was on the news reports from the warships in
the Falklands War. To begin with, the reports were always preceded by an
apology for the poor picture quality - because the ship's rotating radar
pulse stomped a great big noise bar over the picture every couple of
seconds. Of course film would have been immune but there would have been
the "little" problem of taking a film-processing system and telecine ;-)
ENG cameras have to be immune to all *normal* RFI, but immunity from a
megawatt of SHF from a radar wouldn't have been tested for ;-)
Don't know whether it affected the electronics as such (amplifiers etc) or
whether it buggered up the electron beams inside the plumbicon tubes -
because the early 80s were almost certainly before solid-state sensors.

tony sayer

2023-07-22 15:07:42 UTC

You were very lucky if the bloody things worked anyway, piles of the
proverbial poo!..

Forever taking the bloody things X-20 was it down to their place in
Fitzroy street!.

Bloke there let on he'd be buying the rejects from Newmarket transistors
on the cheap!

--
Tony Sayer

Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.

Liz Tuddenham

2023-07-22 16:52:02 UTC

You were very lucky if the bloody things worked anyway, piles of the
proverbial poo!..
Forever taking the bloody things X-20 was it down to their place in
Fitzroy street!.
Bloke there let on he'd be buying the rejects from Newmarket transistors
on the cheap!

I also heard that. A friend of mine briefly worked for Sinclair and
told me that was what he did.

--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

J. P. Gilliver

2023-07-22 18:37:18 UTC

In message <1qea6s8.av88be1pe27ogN%***@poppyrecords.invalid.invalid> at
Sat, 22 Jul 2023 17:52:02, Liz Tuddenham

Post by Brian Gaff
I'm sure we tried that as well. It worked on a tape recorder, but not on
other things. Indeed, those with long memories will recall the Sinclair IC12

[]

Post by tony sayer
Bloke there let on he'd be buying the rejects from Newmarket transistors
on the cheap!

I also heard that. A friend of mine briefly worked for Sinclair and
told me that was what he did.

Conversely, the version of the story _I_ heard was that the transistors
were designed for digital application, so were supposed to have
extremely high gain - either on or off. The ones rejected had a slope
that was further from the vertical, and thus _more_ suited for audio
applications. So yes, he was buying "rejects", but rejects from ones
intended for digital use, not rejects from ones designed as audio
devices in the first place.

--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)***@T+H+Sh0!:`)DNAf

Never make the same mistake twice...there are so many new ones to make!

2023-07-22 14:09:41 UTC

Post by tony sayer
Seen this in a lot of TV audio cars even since waay back on 27 MHz AM CB
systems and mobile phone breakthrough the thermostat arcing the lot!!

My car, or maybe it was the one before it, was prone to picking up 2G
mobile phone "galloping horses" through the radio speakers even with the
radio turned off. But maybe the on/off switch just turned off the
display and front panel, and muted the RF detector input, and the
amplifier was permanently powered.

These days, "galloping horses" are like white dogshit: remembered but
not encountered for yonks.

tony sayer

2023-07-22 15:15:37 UTC

Post by tony sayer
Seen this in a lot of TV audio cars even since waay back on 27 MHz AM CB
systems and mobile phone breakthrough the thermostat arcing the lot!!

My car, or maybe it was the one before it, was prone to picking up 2G
mobile phone "galloping horses" through the radio speakers even with the
radio turned off. But maybe the on/off switch just turned off the
display and front panel, and muted the RF detector input, and the
amplifier was permanently powered.
These days, "galloping horses" are like white dogshit: remembered but
not encountered for yonks.

We used to get a lot of problems with PMR breakthrough in cars electric
windows would go up and down etc!

Worst one was the old police Volvo's 144 model IIRC it seemed the
electronic fuel injection would cause the engine to stall when the radio
was transmitting!...

--
Tony Sayer

Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.

Woody

2023-07-22 15:31:32 UTC

Post by tony sayer
Seen this in a lot of TV audio cars even since waay back on 27 MHz AM CB
systems and mobile phone breakthrough the thermostat arcing the lot!!

My car, or maybe it was the one before it, was prone to picking up 2G
mobile phone "galloping horses" through the radio speakers even with the
radio turned off. But maybe the on/off switch just turned off the
display and front panel, and muted the RF detector input, and the
amplifier was permanently powered.
These days, "galloping horses" are like white dogshit: remembered but
not encountered for yonks.

We used to get a lot of problems with PMR breakthrough in cars electric
windows would go up and down etc!
Worst one was the old police Volvo's 144 model IIRC it seemed the
electronic fuel injection would cause the engine to stall when the radio
was transmitting!...

Not quite Tony - I remember that one distinctly.
The Volvo 144's had the first ever electronic (i.e. transistor switched)
ignition. If the radio (Pye Vanguard of course on 79MHz-ish) transmitted
the car speed dropped by almost exactly 30mph consistently.
The lads at Pye Cambridge Service at Arbury Road cured it with some ease
- they wrapped the 'electronic ignition' plastic box in (grounded)
cooking foil. 100% instant cure!

tony sayer

2023-07-22 15:45:10 UTC

Post by Woody

Post by tony sayer
Seen this in a lot of TV audio cars even since waay back on 27 MHz AM CB
systems and mobile phone breakthrough the thermostat arcing the lot!!

My car, or maybe it was the one before it, was prone to picking up 2G
mobile phone "galloping horses" through the radio speakers even with the
radio turned off. But maybe the on/off switch just turned off the
display and front panel, and muted the RF detector input, and the
amplifier was permanently powered.
These days, "galloping horses" are like white dogshit: remembered but
not encountered for yonks.

We used to get a lot of problems with PMR breakthrough in cars electric
windows would go up and down etc!
Worst one was the old police Volvo's 144 model IIRC it seemed the
electronic fuel injection would cause the engine to stall when the radio
was transmitting!...

I indeed thank my noble friend from 'opp North:).

Who will I'm sure admit this was a long time ago now and the memory?,
well thats what we read in the Cambridge even news IIRC!...

--
Tony Sayer

Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.

charles

2023-07-22 16:30:02 UTC

Post by tony sayer
Seen this in a lot of TV audio cars even since waay back on 27 MHz
AM CB systems and mobile phone breakthrough the thermostat arcing
the lot!!

My car, or maybe it was the one before it, was prone to picking up 2G
mobile phone "galloping horses" through the radio speakers even with
the radio turned off. But maybe the on/off switch just turned off the
display and front panel, and muted the RF detector input, and the
amplifier was permanently powered.
These days, "galloping horses" are like white dogshit: remembered but
not encountered for yonks.

We used to get a lot of problems with PMR breakthrough in cars
electric windows would go up and down etc!
Worst one was the old police Volvo's 144 model IIRC it seemed the
electronic fuel injection would cause the engine to stall when the
radio was transmitting!...

Not quite Tony - I remember that one distinctly. The Volvo 144's had the
first ever electronic (i.e. transistor switched) ignition. If the radio
(Pye Vanguard of course on 79MHz-ish) transmitted the car speed dropped
by almost exactly 30mph consistently. The lads at Pye Cambridge Service
at Arbury Road cured it with some ease - they wrapped the 'electronic
ignition' plastic box in (grounded) cooking foil. 100% instant cure!

I indeed thank my noble friend from 'opp North:).
Who will I'm sure admit this was a long time ago now and the memory?,
well thats what we read in the Cambridge even news IIRC!...

Cambridge Evening News? That brings back memories from 1962. Look in the
archives

--
from KT24 in Surrey, England - sent from my RISC OS 4té
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

Woody

2023-07-22 18:19:25 UTC

Post by tony sayer
Seen this in a lot of TV audio cars even since waay back on 27 MHz AM CB
systems and mobile phone breakthrough the thermostat arcing the lot!!

My car, or maybe it was the one before it, was prone to picking up 2G
mobile phone "galloping horses" through the radio speakers even with the
radio turned off. But maybe the on/off switch just turned off the
display and front panel, and muted the RF detector input, and the
amplifier was permanently powered.
These days, "galloping horses" are like white dogshit: remembered but
not encountered for yonks.

We used to get a lot of problems with PMR breakthrough in cars electric
windows would go up and down etc!
Worst one was the old police Volvo's 144 model IIRC it seemed the
electronic fuel injection would cause the engine to stall when the radio
was transmitting!...

I indeed thank my noble friend from 'opp North:).
Who will I'm sure admit this was a long time ago now and the memory?,
well thats what we read in the Cambridge even news IIRC!...

IIRC I was at the Apprentice Training Centre on the same site at the
time (so 1969-1970,) and one of my trainee colleagues knew the 'Depot'
(as we knew them) Senior Engineer - they were both radio amateurs - so
we got to know about it!

2023-07-22 16:16:32 UTC

Post by Woody
The lads at Pye Cambridge Service at Arbury Road cured it with some ease
- they wrapped the 'electronic ignition' plastic box in (grounded)
cooking foil. 100% instant cure!

I wonder whether a similar might worked with the cameras on the
Falklands warships - wrap camera (except lens) in aluminium foil
connected to ship's metal structure (ie earthed/'watered' hull).

I'm sure it would have been one of the first bodges that the cameramen
would have tried, so I suppose it didn't work. Or maybe what we saw was
*after* that bodge, and things were even worse without it ;-)

Brian

2023-07-23 14:39:28 UTC

Post by Woody
The lads at Pye Cambridge Service at Arbury Road cured it with some ease
- they wrapped the 'electronic ignition' plastic box in (grounded)
cooking foil. 100% instant cure!

I wonder whether a similar might worked with the cameras on the
Falklands warships - wrap camera (except lens) in aluminium foil
connected to ship's metal structure (ie earthed/'watered' hull).

The lens barrel (in that era, at any rate) will have been metallic,
and connected to the body of the camera which will itself have been
earthed at RF by the body of the camera operator, if by no other
means.

If the interference was induced in the camera, then I suspect Rod is
right, and the head amps were the culprits. There is hole cut in the
front of the cam to let the light in. At the sort of frequencies in
question, this will have done just as well to let RF in.

On the side of the target not scanned by the beam there is a very thin
metallic layer - thin enough to be transparent to light, but thick
enough to be conductive. This is where the bias is applied to the
target and also where the signal current leaves the tube for the input
of the head amp. It will work quite effectively as a plate aerial,
albeit a very small one.

Peak white current in the tube is of the order of a couple of hundred
nanoamps. You therefore wouldn't need much RF pickup to drive the
signal into the white clipper.

The other possibility, and I add here the caveat that I don't know the
details of how the location recording was engineered, is that the
radar got into the VT machine.

--
Brian

Beware the spamtrap by Kubrick.

Liz Tuddenham

2023-07-22 16:52:02 UTC

NY <***@privacy.net> wrote:

[...]

Post by NY
These days, "galloping horses" are like white dogshit: remembered but
not encountered for yonks.

I don't remember white dog shit - but that's probably because I have a
terrible memory for faeces.

--
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(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

J. P. Gilliver

2023-07-22 18:32:28 UTC

In message <1qea6vu.1wxcv96150ruyoN%***@poppyrecords.invalid.invalid> at
Sat, 22 Jul 2023 17:52:02, Liz Tuddenham

Post by NY
These days, "galloping horses" are like white dogshit: remembered but
not encountered for yonks.

I don't remember white dog shit - but that's probably because I have a
terrible memory for faeces.

GROAN! Excellent.

(Actually, I was thinking even non-white is somewhat rare these days: I
can only presume the social pressure on owners has actually started to
work.)

--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)***@T+H+Sh0!:`)DNAf

Never make the same mistake twice...there are so many new ones to make!

jon

2023-07-23 07:36:46 UTC

Post by Brian Gaff
I have an amplified Sub woofer, but it seems to be very prone to picking
stuff up. For example, it can pick up switching transients and up until
quite recently, even Radio China International. The Chinese seem to have
lowered their power recently, but back when I first got it, you could
hear Vatican Radio as well, but these days they don't use short waves.
Its interesting to note it does not pick up Premier radio, even though
there is an am outlet less than a mile away.
We tried mains filters internal capacitors everywhere with no effect. It
even did it connected just to the mains and no inputs. I can only deduce
that the power amp design is just wide open and allows most stuff into
the amp where it just gets rectified and shoved out through the speaker.
I once had a Tandberg tuner amp that was like this, and no amount of
suppression would work there either.
Brian

I built a Mullard 5-10 many years ago and that picked up all sorts of
stray stations, with a bit of wire on the input. The EF86 was quite
sensitive.

Brian Gaff

2023-07-23 10:33:51 UTC

Of course Rogers Cadet could do this as well, but it used a slightly
different valve, only made by Mazda. Valve amps are naturally a lot more
high impedance of course.
Brian
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Post by jon

Post by Brian Gaff
I have an amplified Sub woofer, but it seems to be very prone to picking
stuff up. For example, it can pick up switching transients and up until
quite recently, even Radio China International. The Chinese seem to have
lowered their power recently, but back when I first got it, you could
hear Vatican Radio as well, but these days they don't use short waves.
Its interesting to note it does not pick up Premier radio, even though
there is an am outlet less than a mile away.
We tried mains filters internal capacitors everywhere with no effect. It
even did it connected just to the mains and no inputs. I can only deduce
that the power amp design is just wide open and allows most stuff into
the amp where it just gets rectified and shoved out through the speaker.
I once had a Tandberg tuner amp that was like this, and no amount of
suppression would work there either.
Brian

I built a Mullard 5-10 many years ago and that picked up all sorts of
stray stations, with a bit of wire on the input. The EF86 was quite
sensitive.

J. P. Gilliver

2023-07-23 11:05:33 UTC

Post by Brian Gaff
I have an amplified Sub woofer, but it seems to be very prone to picking
stuff up. For example, it can pick up switching transients and up until

[]
I've been very puzzled throughout this thread: surely a sub-woofer
should be pretty low pass? Or is it really an amplified system that
_includes_ a sub-woofer, but mid and high range too?

--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)***@T+H+Sh0!:`)DNAf

I'd rather trust the guys in the lab coats who aren't demanding that I get up
early on Sundays to apologize for being human.
-- Captain Splendid (quoted by "The Real Bev" in mozilla.general, 2014-11-16)

John Williamson

2023-07-23 11:36:55 UTC

Post by J. P. Gilliver

Post by Brian Gaff
I have an amplified Sub woofer, but it seems to be very prone to picking
stuff up. For example, it can pick up switching transients and up until

[]
I've been very puzzled throughout this thread: surely a sub-woofer
should be pretty low pass? Or is it really an amplified system that
_includes_ a sub-woofer, but mid and high range too?

The usual design uses a standard amplifier of the appropriate power
rating, a high pass filter for the pass through to the main speakers and
a low pass for the feed to the sub. (In effect, a low power version of
the crossover found in multi cone speakers). It's cheaper than designing
and building an amplifier that has the low pass filter integral to the
design.

If wanted, it's easy enough to add the occasional capacitor to reduce HF
pickup in an analogue amplifier.

My sub, though, had a class D amplifier, which is not so easy to add
filtering to in the design.

--
Tciao for Now!

John.

Brian Gaff

2023-07-23 17:46:21 UTC

Well in my application, I cannot really run cables to the low power input
and back to the amp to take advantage of the spectrum splitting, but they do
allow it to accept the speaker inputs and have a couple of controls, roll
over and amplitude to integrate it into the existing system, plus a phase
switch. The amps are fairly standard push pull types with a plus and minus
supply and a centre earth.
I will have to replace the power switch on relay though as its sealed and
drops out energising the protection and the whole lot goes off.
That is a side issue though. Its always been prone to this audio
breakthrough, and although as i mentioned it has filtering, that is
obviously part of the circuit and hence there is probably a transistor or
two before that part of the circuit.
Brian
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