Is this an FM aerial? Where did it come from?

[d***@postmaster.co.uk]

Appologies for the cross posting, but despite this being OT for three
of these groups, these are the groups where I know people can answer
this question!

Right, sad aerial spotting time...

Is this an FM aerial?
Loading Image...
Loading Image...

I've seen one like this (but about twice as long, hence twice as many
elements!!!) on top of a house in a village somewhere, but didn't have
my camera with me.

The example I've photographed is on the top of a hi-fi shop in Hitchin,
Herts, UK, but the only aerial that _they_ know is on their roof is "a
high gain digital TV aerial" (which this probably, unless DTT is still
on VHF in Hitchin!).

So what is this aerial, and where was it bought from? Can they still be
bought? What is the advantage, if any, over the standard folded dipole
and several elements which make up most directional FM aerials?
Cheers,
David.

[Mike Gilmour]

Post by d***@postmaster.co.uk
Appologies for the cross posting, but despite this being OT for three
of these groups, these are the groups where I know people can answer
this question!
Right, sad aerial spotting time...
Is this an FM aerial?
http://www.david.robinson.org/pics/aerial1.jpg
http://www.david.robinson.org/pics/aerial2.jpg
I've seen one like this (but about twice as long, hence twice as many
elements!!!) on top of a house in a village somewhere, but didn't have
my camera with me.
The example I've photographed is on the top of a hi-fi shop in Hitchin,
Herts, UK, but the only aerial that _they_ know is on their roof is "a
high gain digital TV aerial" (which this probably, unless DTT is still
on VHF in Hitchin!).
So what is this aerial, and where was it bought from? Can they still be
bought? What is the advantage, if any, over the standard folded dipole
and several elements which make up most directional FM aerials?
Cheers,
David.

For broadcast FM, I believe its a Galaxie Model G.17 with 10 reflectors,
cicular dipole and six directors. 74" long with a gain of 15.9 dB and 45 deg
acceptance angle. I have the G.20 above my roof which is 30" longer than the
G17 gives extra 2dB extra gain and 28 degree acceptance angle. Sourced mine
from Ron Smith Luton Beds UK. The reason for mine is a) I'm in the Scottish
Highlands b) it feeds a good tuner Magnum Dynalab 'Etude'. The advantage
for me is mainly gain & a good clean signal.
Hope this helps,

Mike

[T]

Post by Mike Gilmour
For broadcast FM, I believe its a Galaxie Model G.17 with 10 reflectors,
cicular dipole and six directors. 74" long with a gain of 15.9 dB and 45 deg
acceptance angle.

<snip>

I can tell all this by looking at it....


Man, my hat is off Mike.


TBerk

[Mike Gilmour]

Post by T

Post by Mike Gilmour
For broadcast FM, I believe its a Galaxie Model G.17 with 10
reflectors, cicular dipole and six directors. 74" long with a gain of
15.9 dB and 45 deg acceptance angle.

<snip>
I can tell all this by looking at it....
Man, my hat is off Mike.
TBerk

Nah, details were written down on the back of an old envelope after I
phoned Ron and I'd filed it with his bill. Had this aerial for about 15
years on a chimney clamped 4m pole and its stood up to gales so far..

Mike.

[d***@postmaster.co.uk]

Post by Mike Gilmour
Nah, details were written down on the back of an old envelope after I
phoned Ron and I'd filed it with his bill. Had this aerial for about 15
years on a chimney clamped 4m pole and its stood up to gales so far..

Thanks for all the interesting and informative replies - especially
Mike's which hit Google 30 minutes after I'd posted the original
question!

I've visited Ron's website and ordered the catalogue.

It's interesting that two people suggest a normal dipole or yagi may be
better. If I just need a dipole or very small yagi, then I might just
dare to attack our brick work (though I'm not going up the chimney, or
sending anyone else up there). It's a difficult choice: simple outdoor
aerial (at loft height) or better aerial in the loft itself. Obviously
it's easier to put something in the loft, but if that something costs
more and does less, it's a waste of time. (See also the Bow Brickhill
thread in uk.tech.broadcast for other issues!).
I guess I'll just have to bite the bullet and try!

Cheers,
David.

[DAB sounds worse than FM]

Post by d***@postmaster.co.uk
If I just need a dipole or very small yagi, then I might
just dare to attack our brick work (though I'm not going up the
simple outdoor aerial (at loft height) or better aerial in the loft
itself. Obviously it's easier to put something in the loft, but if
that something costs more and does less, it's a waste of time.

Yeah, if you look at the aerial (forward) gains for Antiference's
3-element (FM1083) and 5-element (FM1085) yagis:

http://www.antiference.co.uk/fm108.htm

they're 5.0 dBd and 6.9 dBd (dBd is dB relative to a dipole), and you'd
lose the additional 1.9 dB due to the signal having to pass through the
roof.

If I were you I'd go for an Antiference FM1083:

http://cpc.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=AFFM1083&N=401

and install it outside.

[charles]

Post by DAB sounds worse than FM

Post by d***@postmaster.co.uk
If I just need a dipole or very small yagi, then I might
just dare to attack our brick work (though I'm not going up the
simple outdoor aerial (at loft height) or better aerial in the loft
itself. Obviously it's easier to put something in the loft, but if
that something costs more and does less, it's a waste of time.

Yeah, if you look at the aerial (forward) gains for Antiference's
http://www.antiference.co.uk/fm108.htm
they're 5.0 dBd and 6.9 dBd (dBd is dB relative to a dipole), and you'd
lose the additional 1.9 dB due to the signal having to pass through the
roof.

Only 1.9dB through the roof? It depends very much on what the roof is made
of. Modern concrete tiles have a high metallic content - especially the red
ones (the red colour comes from iron oxide). Some others have wire
reinforcement inside. Lead roofs are pretty bad too.

[tony sayer]

Post by d***@postmaster.co.uk

Post by Mike Gilmour
Nah, details were written down on the back of an old envelope after

I

Post by Mike Gilmour
phoned Ron and I'd filed it with his bill. Had this aerial for about

15

Post by Mike Gilmour
years on a chimney clamped 4m pole and its stood up to gales so far..

Thanks for all the interesting and informative replies - especially
Mike's which hit Google 30 minutes after I'd posted the original
question!
I've visited Ron's website and ordered the catalogue.
It's interesting that two people suggest a normal dipole or yagi may be
better. If I just need a dipole or very small yagi, then I might just
dare to attack our brick work (though I'm not going up the chimney, or
sending anyone else up there). It's a difficult choice: simple outdoor
aerial (at loft height) or better aerial in the loft itself. Obviously
it's easier to put something in the loft, but if that something costs
more and does less, it's a waste of time. (See also the Bow Brickhill
thread in uk.tech.broadcast for other issues!).
I guess I'll just have to bite the bullet and try!

David, Stop being a wuss and get up 'thar on either that chimney or wall
and hang on there something like a 4 element TRIAX available from
www.cpc.co.uk.

If your wall and or chimney is capable of even standing then either
would support such an aerial. It would work for what you want it to do
much better then either one of Rons big jobs or faffing around with
aerials in the loft.

If you can't do it then get a half decent aerial rigger in to do it.
Make sure he uses CT100 don't be fobbed off with anything less and don't
rely on him to provide the aerial either, as it'll be a cheapie contract
jobbie and whatEVER you do don't be tempted into one of those HALO
pieces of crap.

Then sit back and enjoy the radio for several years to come. Write off
the money on your well installed unit over say 10 years and then see
what good value for money that really is:))

[charles]

Post by tony sayer
Then sit back and enjoy the radio for several years to come. Write off
the money on your well installed unit over say 10 years and then see
what good value for money that really is:))

My Fuba UKA5 has been up since 1978. It still seems to provide a good
signal.

You pays your money and you takes your choice.

[Arthur]

Post by tony sayer

Post by d***@postmaster.co.uk
It's interesting that two people suggest a normal dipole or yagi may be
better. If I just need a dipole or very small yagi, then I might just
dare to attack our brick work (though I'm not going up the chimney, or
sending anyone else up there). It's a difficult choice: simple outdoor
aerial (at loft height) or better aerial in the loft itself. Obviously
it's easier to put something in the loft, but if that something costs
more and does less, it's a waste of time. (See also the Bow Brickhill
thread in uk.tech.broadcast for other issues!).
I guess I'll just have to bite the bullet and try!

David, Stop being a wuss and get up 'thar on either that chimney or wall
and hang on there something like a 4 element TRIAX available from
www.cpc.co.uk.

David, if you are getting satisfactory reception from your dipole, why do
you want to put up a huge, heavy and expensive multi-element array?
Your nearest BBC FM radio site is only 20km away and is designed to give
satisfactory reception on a portable or mobile receiver in your area, so
your rooftop dipole is more than adequate. The main independent radio
channels also provide a normal service in your area.
If you are interested for some reason in receiving distant stations
outside their service areas then you will need a high-gain aerial, but you
will then probably also need a rotator to drive it.

Is this what you *really* need?

Arthur

[charles]

Post by Arthur
David, if you are getting satisfactory reception from your dipole, why do
you want to put up a huge, heavy and expensive multi-element array?
Your nearest BBC FM radio site is only 20km away and is designed to give
satisfactory reception on a portable or mobile receiver in your area, so
your rooftop dipole is more than adequate.

I hate to disagree with a former colleague, but the BBC always said that for
decent stereo a minimum of two elements is needed to protect against
mutipath.

I confirm what some people have said regarding Ron Smith aerials, they seem
to be very good at creating multipath where none should exist.

[Mark Carver]

Post by charles
I hate to disagree with a former colleague, but the BBC always said that for
decent stereo a minimum of two elements is needed to protect against
mutipath.

Strange then that in recent years BBC FM relay stations have employed
vertical only polarization. A VP two element yagi will probably pick up
more signals from unwanted directions, than one HP ?

Think about the polar response charts for each plane.

[charles]

Post by Mark Carver

Post by charles
I hate to disagree with a former colleague, but the BBC always said
that for decent stereo a minimum of two elements is needed to protect
against mutipath.

Strange then that in recent years BBC FM relay stations have employed
vertical only polarization.

This was done on ground of cost, I regret, rather than on technical quality.
Often the existing mast could take the loading of an HP aerial, but not an
MP one (or ones).

Post by Mark Carver
A VP two element yagi will probably pick up more signals from unwanted
directions, than one HP ?

It should have the same rejection towards the rear - which was the reason
for suggesting a two element aerial.

[tony sayer]

Post by Arthur

Post by tony sayer

Post by d***@postmaster.co.uk
It's interesting that two people suggest a normal dipole or yagi may be
better. If I just need a dipole or very small yagi, then I might just
dare to attack our brick work (though I'm not going up the chimney, or
sending anyone else up there). It's a difficult choice: simple outdoor
aerial (at loft height) or better aerial in the loft itself. Obviously
it's easier to put something in the loft, but if that something costs
more and does less, it's a waste of time. (See also the Bow Brickhill
thread in uk.tech.broadcast for other issues!).
I guess I'll just have to bite the bullet and try!

David, Stop being a wuss and get up 'thar on either that chimney or wall
and hang on there something like a 4 element TRIAX available from
www.cpc.co.uk.

David, if you are getting satisfactory reception from your dipole, why do
you want to put up a huge, heavy and expensive multi-element array?
Your nearest BBC FM radio site is only 20km away and is designed to give
satisfactory reception on a portable or mobile receiver in your area, so
your rooftop dipole is more than adequate. The main independent radio
channels also provide a normal service in your area.
If you are interested for some reason in receiving distant stations
outside their service areas then you will need a high-gain aerial, but you
will then probably also need a rotator to drive it.
Is this what you *really* need?

What he really needs is an outside aerial up in the clear, and one that
has some element of directivity and gain, so that his tuner is receiving
a clean feed free from reflections, which unlike ghosting on an analogue
TV aren't so apparent on FM, but they do affect the received audio.

Preferably a bit more gain so that under lift conditions etc he will
have some measure of discrimination against interferer signals and for
the times when you local TX might go on low power, or fall over and be
seemingly on reduced power from here to god knows when!, so all in all
not a too demanding requirement.

Course, if you feel you need one of Ron S's jobbies, on your head be it
especially if that wall's as bad as he reckons.

[charles]

Post by tony sayer
Preferably a bit more gain so that under lift conditions etc he will
have some measure of discrimination against interferer signals

Gain, as such, won't give any benefit against long distance signals since
they will benefit from the extra gain just as much as the wanted ones.
However, to get more gain you normally narrow the angle of acceptance and it
is this that may give discrimination against unwanted signals.

Post by tony sayer
and for the times when you local TX might go on low power, or fall over
and be seemingly on reduced power from here to god knows when!, so all in
all not a too demanding requirement.

agreed.

[tony sayer]

Post by charles

Post by tony sayer
Preferably a bit more gain so that under lift conditions etc he will
have some measure of discrimination against interferer signals

Gain, as such, won't give any benefit against long distance signals since
they will benefit from the extra gain just as much as the wanted ones.

If their in that same direction then yes, 'tho their not always. One was
merely pointing out that if your going to bother with this, then do it
right;)

Post by charles
However, to get more gain you normally narrow the angle of acceptance and it
is this that may give discrimination against unwanted signals.

Yep!..

Post by charles

Post by tony sayer
and for the times when you local TX might go on low power, or fall over
and be seemingly on reduced power from here to god knows when!, so all in
all not a too demanding requirement.

agreed.

[DAB sounds worse than FM]

Post by Arthur
David, if you are getting satisfactory reception from your dipole,
why do you want to put up a huge, heavy and expensive multi-element
array? Your nearest BBC FM radio site is only 20km away and is
designed to
give satisfactory reception on a portable or mobile receiver in your
area, so your rooftop dipole is more than adequate.

I don't think David has a rooftop dipole, though. Assuming he's just got
an internal wire aerial for FM, if he installed an external dipole or
Yagi he could vastly improve the SNR of the stations he wants to
receive.

[d***@postmaster.co.uk]

Post by DAB sounds worse than FM
I don't think David has a rooftop dipole, though. Assuming he's just got
an internal wire aerial for FM, if he installed an external dipole or
Yagi he could vastly improve the SNR of the stations he wants to
receive.

If I had a simple roof-top vertical dipole, I think I'd have to filter
out or reduce the two local stations before distributing the signal -
they're spectacularly strong. Still, that may be the case with whatever
I buy.

Cheers,
David.

[DAB sounds worse than FM]

Post by d***@postmaster.co.uk

Post by DAB sounds worse than FM
I don't think David has a rooftop dipole, though. Assuming he's just
got an internal wire aerial for FM, if he installed an external
dipole or
Yagi he could vastly improve the SNR of the stations he wants to
receive.

If I had a simple roof-top vertical dipole, I think I'd have to filter
out or reduce the two local stations before distributing the signal -
they're spectacularly strong. Still, that may be the case with
whatever I buy.

Depending on the angles of the transmitter you want to receive signals
from and the transmitter with the local stations that you don't want to
receive, then if you got a Yagi then it may do the filtering for you due
to the directional radiation pattern of the aerial.

If you look at typical antenna radiation patterns:

http://www.gigaant.com/?id=246&show=434

these patterns are in the horizontal plane, so the omni-directional
vertical dipole has a circular radiation pattern, because it has the
same antenna gain in all directions. The radiation pattern superimposed
on the dipole's pattern is for a directional aerial such as a Yagi
(although the main lobe is quite narrow, so it's likely to have quite a
few elements). But the important thing as far as filtering-out signals
go is that if the unwanted signal is coming from an angle, say, 60
degrees relative to the desired signal then it's in one of the nulls of
the antenna pattern, so it's pretty effectively filtered out, because
the relative attenuation is the gain of the main lobe (which will be
pointing at the desired transmitter) minus the gain at the undesired
angle which, as you can see from that diagram, can be quite significant.

Here's some more info on radiation patterns:

http://www.astronantennas.com/radiation_patterns.html

Antiference say the acceptance angle of their FM1083 3-element Yagi is
32 degrees, and they define acceptance angle here:

http://www.antiference.co.uk/def.htm

as:

"the angle from the centre line to the point where the signal falls to
half power (-3dB)"

The front to back ratio is specified as being 15dB, so if the unwanted
signals were coming from the opposite direction to the desired signals
then you've got 15dB of attenuation from the front-to-back ratio, and
looking at a radiation pattern for a Yagi in a book I've got, the back
lobe has the highest gain.

Sack this, they say a picture tells a thousand words, so I've done a
graph:

http://www.digitalradiotech.co.uk/antenna_pattern.htm

(There's a null (theoretically infinite loss) at +90 and -90 degrees, so
to make the graph look right I've arbitrarily allocated a gain of -40
dB.)

I don't know what exact antenna that is for, because it doesn't say what
antenna it's for in the book other than it's a Yagi. But that'll be the
typical shape of the graph of gain against direction. So, try and find
out what the relative angles are of the transmitter that you want to
receive from and the transmitter that the local stations are on which
you don't want, and if you're lucky the unwanted signals may be coming
from angles where they'd be filtered by the antenna pattern of a Yagi.

[Arthur]

On Thu, 20 Jan 2005 13:53:12 GMT, DAB sounds worse than FM
<***@low.quality> wrote:

(sound advice snipped)

Post by DAB sounds worse than FM
if you're lucky the unwanted signals may be coming
from angles where they'd be filtered by the antenna pattern of a Yagi.

If you aim the aerial to drop one of the "spectacularly strong" local
transmitters into a notch, this will certainly help in listening to weaker
stations. But when listening to the local station itself you may be
beaming at a reflected signal with comparable strength to the direct
signal. This can cause appalling distortion to FM audio reception.

Arthur

[DAB sounds worse than FM]

Post by Arthur
On Thu, 20 Jan 2005 13:53:12 GMT, DAB sounds worse than FM
(sound advice snipped)

Post by DAB sounds worse than FM
if you're lucky the unwanted signals may be coming
from angles where they'd be filtered by the antenna pattern of a Yagi.

If you aim the aerial to drop one of the "spectacularly strong" local
transmitters into a notch, this will certainly help in listening to
weaker stations. But when listening to the local station itself you
may be beaming at a reflected signal with comparable strength to the
direct signal. This can cause appalling distortion to FM audio
reception.

Fair enough. Mark Carver said it might be these: Chiltern 96.9 and BBC
3CR 95.5, so I assumed he wouldn't want to ever listen to them. ;)

[Mark Carver]

Post by DAB sounds worse than FM

Post by Arthur
If you aim the aerial to drop one of the "spectacularly strong" local
transmitters into a notch, this will certainly help in listening to
weaker stations. But when listening to the local station itself you
may be beaming at a reflected signal with comparable strength to the
direct signal. This can cause appalling distortion to FM audio
reception.

Fair enough. Mark Carver said it might be these: Chiltern 96.9 and BBC
3CR 95.5, so I assumed he wouldn't want to ever listen to them. ;)

I did, I only posted that reply in alt.radio.digital, so to avoid
confusion I suggested making a couple of quarter wave stub filters, and
place them in the downlead.

[w***@aol.com]

I suggested making a couple of quarter wave stub filters

http://www.wrightsaerials.tv/Resources/VHF%20Interference.pdf
has a bit of info about this.

Bill

[Richard Fry]

Post by Mark Carver
I suggested making a couple of quarter wave stub filters

___________

However the reject bandwidth of such filters is rather broad, and they can
introduce significant losses on many FM channels beside the one(s) targeted.
Also their sloping RF amplitude response and differential RF group delay
across the nearby channels will add stereo crosstalk and distortion to
stations received on those channels.

RF

Visit http://rfry.org for FM transmission system papers.

[Arthur]

Post by Mark Carver
I suggested making a couple of quarter wave stub filters
http://www.wrightsaerials.tv/Resources/VHF%20Interference.pdf
has a bit of info about this.
Bill

Are you sure it would have a sufficiently high 'Q'? I think you'd need a
cavity resonator.

Arthur

[Mark Carver]

Post by Mark Carver
I suggested making a couple of quarter wave stub filters
http://www.wrightsaerials.tv/Resources/VHF%20Interference.pdf
has a bit of info about this.
Bill

Are you sure it would have a sufficiently high 'Q'? I think you'd need a cavity resonator.

I used one with success to reduce a strong TV carrier (UHF E31) that was splashing
across on a much weaker one (E34). It didn't impair the level of the E34 carrier noticably,
and the E31 carrier (also wanted) was still usable. That's a 24 MHz range in 550ish MHz.
I suppose scaling that down to the OP's problem in Band II might be expecting too much ?

One advantage is that it's very cheap (just off cuts of co-ax and a bit of soldering) to try :-)

[DAB sounds worse than FM]

Post by Mark Carver
One advantage is that it's very cheap (just off cuts of co-ax and a
bit of soldering) to try :-)

I take it this is a short-circuit quarter-wave stub?

What do you connect to what? That is, what do you connect each end of
the inner conductor to and what do you connect each end of the outer
conductor to?

[Mark Carver]

Post by DAB sounds worse than FM

Post by Mark Carver
One advantage is that it's very cheap (just off cuts of co-ax and a
bit of soldering) to try :-)

I take it this is a short-circuit quarter-wave stub?

No, open circuit

Post by DAB sounds worse than FM
What do you connect to what? That is, what do you connect each end of
the inner conductor to and what do you connect each end of the outer
conductor to?

See page 4 from Bill's web page
http://www.wrightsaerials.tv/Resources/VHF%20Interference.pdf

However, as Richard L has suggested elsewhere in this thread, a half
wave stub might be an easier option. Same connection details, except
it's twice as long as a quarter wave, and the end is short circuited.

[DAB sounds worse than FM]

Post by Mark Carver

Post by DAB sounds worse than FM

Post by Mark Carver
One advantage is that it's very cheap (just off cuts of co-ax and a
bit of soldering) to try :-)

I take it this is a short-circuit quarter-wave stub?

No, open circuit

Ah well, I had a 50% chance of getting it right. :)

Post by Mark Carver

Post by DAB sounds worse than FM
What do you connect to what? That is, what do you connect each end of
the inner conductor to and what do you connect each end of the outer
conductor to?

See page 4 from Bill's web page
http://www.wrightsaerials.tv/Resources/VHF%20Interference.pdf

It's surprisingly effective innit. At first, you look at the frequency
response in Figure 8 on page 4 and you think it's going to negatively
effect the the signals on all the other channels too much.

As well as adding a stub filter, I still think David should get a Yagi,
though, because if he wants to hear how good FM can be then the extra
5dB gain relative to a dipole can't hurt, and I think he mainly listens
to BBC network stations, so I assume they'll all come from the same
transmitter.

BTW, what is the effect / how much loss is caused by not using a balun
to connect a dipole to coax?

[Mark Carver]

Post by DAB sounds worse than FM
As well as adding a stub filter, I still think David should get a Yagi,
though, because if he wants to hear how good FM can be then the extra
5dB gain relative to a dipole can't hurt, and I think he mainly listens
to BBC network stations, so I assume they'll all come from the same
transmitter.

I think not, unwanted locals are from Sandy Heath, wanted nationals from
Peterborough ?

Post by DAB sounds worse than FM
BTW, what is the effect / how much loss is caused by not using a balun
to connect a dipole to coax?

Oooh, you're almost into chaos theory there I think ?

[DAB sounds worse than FM]

Post by Mark Carver

Post by DAB sounds worse than FM
As well as adding a stub filter, I still think David should get a
Yagi, though, because if he wants to hear how good FM can be then
the extra 5dB gain relative to a dipole can't hurt, and I think he
mainly listens to BBC network stations, so I assume they'll all come
from the same transmitter.

I think not, unwanted locals are from Sandy Heath, wanted nationals
from Peterborough ?

No, I meant that the BBC network FM stations (Radios 1-4) will all be on
the same transmitter.

Post by Mark Carver

Post by DAB sounds worse than FM
BTW, what is the effect / how much loss is caused by not using a
balun to connect a dipole to coax?

Oooh, you're almost into chaos theory there I think ?

In other words, it's not particularly important?

[Mark Carver]

Post by DAB sounds worse than FM

Post by Mark Carver
I think not, unwanted locals are from Sandy Heath, wanted nationals
from Peterborough ?

No, I meant that the BBC network FM stations (Radios 1-4) will all be on
the same transmitter.

Ah sorry, yes.

Post by DAB sounds worse than FM

Post by Mark Carver

Post by DAB sounds worse than FM
BTW, what is the effect / how much loss is caused by not using a
balun to connect a dipole to coax?

Oooh, you're almost into chaos theory there I think ?

In other words, it's not particularly important?

Oh yes it can be, it's just not easily calculatable.

[DAB sounds worse than FM]

Post by Mark Carver

Post by DAB sounds worse than FM

Post by Mark Carver

Post by DAB sounds worse than FM
BTW, what is the effect / how much loss is caused by not using a
balun to connect a dipole to coax?

Oooh, you're almost into chaos theory there I think ?

In other words, it's not particularly important?

Oh yes it can be, it's just not easily calculatable.

Fair enough. Guestimates of the loss caused by not using one going from
a dipole to coax would be perfectly acceptable.

[Richard L]

Post by DAB sounds worse than FM
No, I meant that the BBC network FM stations (Radios 1-4) will all be on
the same transmitter.

You're confusing this with DAB. The BBC network FM stations are
not all on the same transmitter. But they're all at the same site.

;-)

[Arthur]

On Fri, 21 Jan 2005 12:09:58 GMT, DAB sounds worse than FM

Post by DAB sounds worse than FM
BTW, what is the effect / how much loss is caused by not using a balun
to connect a dipole to coax?

Impossible to quantify, but the effects are all those that you might
expect from a mismatch:

-degradation of the polar diagram
-inefficient power transfer
-pickup of unwanted signals on the feeder
-re-radiation of received signal from the feeder

The amount of each effect will depend on the type of aerial and how it and
the feeder are mounted.

In spite of all the above, a balanced aerial will seem to work
satisfactorily without a balun in a surprising proportion of cases.

Arthur

[Richard Fry]

Post by Arthur

Post by DAB sounds worse than FM
effect / how much loss is caused by not using a balun
to connect a dipole to coax?

Impossible to quantify, but the effects are all those that you might
-degradation of the polar diagram
-inefficient power transfer
-pickup of unwanted signals on the feeder
-re-radiation of received signal from the feeder

________________

However even a perfect balun does not remove the above effects -- because
the outside of the outer conductor of the coax feedline still will be
coupled into the fields received and/or radiated by the aerial, even when
there is no current flowing into the coax outer conductor via a metallic
connection directly with the aerial itself.

As an illustration of this, consider the effect of a 1/2-wave dipole
suspended near, and parallel to another 1/2-wave dipole. Only one dipole is
driven. For simplicity of concept, let's say the active RF device (either a
tx or rx) is a physically small unit built in to the center insulator of the
driven dipole, e.g., no feedline. Standard equations, and NEC-2 analysis
show that considerable interaction exists between the two dipoles. The
input match of the driven dipole changes, and the radiation pattern of the
simple dipole is strongly affected. Yet the only coupling between these two
dipoles is by radiation.

This reality is used to good effect in the design of many types of aerials
(Yagis, etc).

RF

Visit http://rfry.org for FM transmission system papers.

[Arthur]

Post by Richard Fry

Post by Arthur

Post by DAB sounds worse than FM
effect / how much loss is caused by not using a balun
to connect a dipole to coax?

Impossible to quantify, but the effects are all those that you might
-degradation of the polar diagram
-inefficient power transfer
-pickup of unwanted signals on the feeder
-re-radiation of received signal from the feeder

________________
However even a perfect balun does not remove the above effects --
because the outside of the outer conductor of the coax feedline still
will be coupled into the fields received and/or radiated by the aerial,
even when there is no current flowing into the coax outer conductor via
a metallic connection directly with the aerial itself.
As an illustration of this, consider the effect of a 1/2-wave dipole
suspended near, and parallel to another 1/2-wave dipole. Only one
dipole is driven. For simplicity of concept, let's say the active RF
device (either a tx or rx) is a physically small unit built in to the
center insulator of the driven dipole, e.g., no feedline. Standard
equations, and NEC-2 analysis show that considerable interaction exists
between the two dipoles. The input match of the driven dipole changes,
and the radiation pattern of the simple dipole is strongly affected.
Yet the only coupling between these two dipoles is by radiation.
This reality is used to good effect in the design of many types of
aerials (Yagis, etc).
RF
Visit http://rfry.org for FM transmission system papers.

But you are discussing a parasitic element *in parallel" with the fed
dipole. In practice the feeder from the dipole should be run
perpendicularly to its centre, and will therefore have a minimal electric
field generated in its outer.

Arthur

[tony sayer]

Post by Richard Fry
As an illustration of this, consider the effect of a 1/2-wave dipole
suspended near, and parallel to another 1/2-wave dipole. Only one dipole is
driven. For simplicity of concept, let's say the active RF device (either a
tx or rx) is a physically small unit built in to the center insulator of the
driven dipole, e.g., no feedline. Standard equations, and NEC-2 analysis
show that considerable interaction exists between the two dipoles.

Yes course they will..

Post by Richard Fry
The
input match of the driven dipole changes, and the radiation pattern of the
simple dipole is strongly affected. Yet the only coupling between these two
dipoles is by radiation.
This reality is used to good effect in the design of many types of aerials
(Yagis, etc).

Yes, but in practice with a horizontally polarised Yagi with the feeder
tied to the boom and down the mounting mast?.

Or even inside the mounting boom! ...

[Arthur]

Post by Mark Carver
I used one with success to reduce a strong TV carrier (UHF E31) that was splashing
across on a much weaker one (E34). It didn't impair the level of the E34 carrier noticably,
and the E31 carrier (also wanted) was still usable. That's a 24 MHz range in 550ish MHz.
I suppose scaling that down to the OP's problem in Band II might be expecting too much ?
One advantage is that it's very cheap (just off cuts of co-ax and a bit
of soldering) to try :-)

I've also used it successfully for Band I and Band IV TV signals, but I
think it's asking a bit much for this to work with closely-spaced,
relatively narrow-band FM signals in Band II.
I would suggest that if the transmissions are sufficiently spaced in
frequency for a stub to be effective, the FM tuner should itself have
sufficient selectivity and dynamic range to work without the stub.

Arthur

[Arthur]

Very sorry about these double postings - I'm pushing a beta version of a
newsreader to/over the limit!

Arthur

[tony sayer]

Post by Arthur

Post by Mark Carver
I used one with success to reduce a strong TV carrier (UHF E31) that was splashing
across on a much weaker one (E34). It didn't impair the level of the E34
carrier noticably,
and the E31 carrier (also wanted) was still usable. That's a 24 MHz range in 550ish MHz.
I suppose scaling that down to the OP's problem in Band II might be expecting too much ?
One advantage is that it's very cheap (just off cuts of co-ax and a bit
of soldering) to try :-)

I've also used it successfully for Band I and Band IV TV signals, but I
think it's asking a bit much for this to work with closely-spaced,
relatively narrow-band FM signals in Band II.
I would suggest that if the transmissions are sufficiently spaced in
frequency for a stub to be effective, the FM tuner should itself have
sufficient selectivity and dynamic range to work without the stub.
Arthur

We had to get one of these done recently to "notch" out an FM TX from an
RX on the same site 800 kHz apart!.

Works very well, made by aerial facilities www.aerial.co.uk

Cost around 480 squids IIRC;)

[Arthur]

Post by tony sayer
We had to get one of these done recently to "notch" out an FM TX from an
RX on the same site 800 kHz apart!.
Works very well, made by aerial facilities www.aerial.co.uk
Cost around 480 squids IIRC;)

Yes, they make very good ones - silver plated inside.

Arthur

[d***@postmaster.co.uk]

On Fri, 21 Jan 2005 07:39:48 -0000, Mark Carver
I've also used it successfully for Band I and Band IV TV signals, but I
think it's asking a bit much for this to work with closely-spaced,
relatively narrow-band FM signals in Band II.
I would suggest that if the transmissions are sufficiently spaced in
frequency for a stub to be effective, the FM tuner should itself have
sufficient selectivity and dynamic range to work without the stub.

We're only about 3 miles from Sandy Heath. I'm not worried about the
tuner - it's the distribution amplifier (not bought yet) that I suspect
would be overloaded, which would give nice cross mod of BBC 3CR and
Chiltern all across the FM band.

All I can do is try. When I have something in place, I'll come back and
seek advice if the problem manifests itself. I've read Bill's excellent
article, and will try both 1/4 and 1/2 wave stubs first to try to solve
the problem.

Thanks for all the advice everyone.

Cheers,
David.
P.S. suggestions for suitable DA with good headroom where no gain is
required would be gratefully received.

[Marky P]

Post by d***@postmaster.co.uk

On Fri, 21 Jan 2005 07:39:48 -0000, Mark Carver
I've also used it successfully for Band I and Band IV TV signals, but

I

think it's asking a bit much for this to work with closely-spaced,
relatively narrow-band FM signals in Band II.
I would suggest that if the transmissions are sufficiently spaced in
frequency for a stub to be effective, the FM tuner should itself have
sufficient selectivity and dynamic range to work without the stub.

We're only about 3 miles from Sandy Heath. I'm not worried about the
tuner - it's the distribution amplifier (not bought yet) that I suspect
would be overloaded, which would give nice cross mod of BBC 3CR and
Chiltern all across the FM band.
All I can do is try. When I have something in place, I'll come back and
seek advice if the problem manifests itself. I've read Bill's excellent
article, and will try both 1/4 and 1/2 wave stubs first to try to solve
the problem.
Thanks for all the advice everyone.
Cheers,
David.
P.S. suggestions for suitable DA with good headroom where no gain is
required would be gratefully received.

What is the distribution amp for? Are you planning to feed multiple
tuners? If so, it may be possible just to use a passive splitter with
very little loss in signal. This way you shouldn't get overload from
Sandy. I would recommend a 4 element aerial at least if this was the
case. If you plan on pointing it Peterborough (which from where you
are is roughly in the same direction as Sandy?) you should get a
perfect signal, at least when it's up & running again!)

Marky P.

[Richard L]

Post by Mark Carver
I suggested making a couple of quarter wave stub filters
http://www.wrightsaerials.tv/Resources/VHF%20Interference.pdf
has a bit of info about this.

But if you're snipping bits off a quarter-wave stub, you can't be
certain you've found the right length until you've gone past it.
From a practical point of view, I've always preferred the
half-wave stub, shorted at the end. You can make the short by
experimentally pushing a hatpin through the cable at successive
points to locate the spot which kills the frequency of interest.

[Richard Fry]

Post by DAB sounds worse than FM
Depending on the angles of the transmitter you want to receive signals
from and the transmitter with the local stations that you don't want to
receive, then if you got a Yagi then it may do the filtering for you due
to the directional radiation pattern of the aerial. (etc)

_________________

Other considerations are the frequency separation between the desired and
undesired station, and the field strength of the undesired station.

A very strong local station on a nearby freq can de-sensitise a receiver,
making it difficult to receive adjacent channels. The carrier ratio between
local and distant stations easily can be 50dB or more.

Even the best FM rx antenna will have difficulty reducing the field strength
of the local station below that of the distant one. Reflections of the
local station can arrive via multipath along with the distant station, on
the pointing axis of the rx antenna. The reflection itself may only be
10-15 dB reduced from the direct wave -- still far above that of the distant
station -- and there is no way to get rid of it using the antenna pattern
alone.

There are methods of introducing a sample of the interfering signal into the
output of the rx antenna line, and adjusting its amplitude and phase so as
to null the interfering RF wave. Usually this is not practical for other
than commercial applications.

RF

Visit http://rfry.org for FM transmission system papers.

[DAB sounds worse than FM]

Post by Richard Fry

Post by DAB sounds worse than FM
Depending on the angles of the transmitter you want to receive
signals from and the transmitter with the local stations that you
don't want to receive, then if you got a Yagi then it may do the
filtering for you due to the directional radiation pattern of the
aerial. (etc) _________________

Other considerations are the frequency separation between the desired
and undesired station, and the field strength of the undesired
station.
A very strong local station on a nearby freq can de-sensitise a
receiver, making it difficult to receive adjacent channels. The
carrier ratio between local and distant stations easily can be 50dB
or more.
Even the best FM rx antenna will have difficulty reducing the field
strength of the local station below that of the distant one.
Reflections of the local station can arrive via multipath along with
the distant station, on the pointing axis of the rx antenna. The
reflection itself may only be 10-15 dB reduced from the direct wave
-- still far above that of the distant station -- and there is no way
to get rid of it using the antenna pattern alone.
There are methods of introducing a sample of the interfering signal
into the output of the rx antenna line, and adjusting its amplitude
and phase so as to null the interfering RF wave. Usually this is not
practical for other than commercial applications.

Very interesting, thanks.

[Paul Martin]

Post by tony sayer
whatEVER you do don't be tempted into one of those HALO
pieces of crap.

If you're next to Holme Moss, it won't matter... but then if you're
in that situation a nail would work as well.

[Doug McDonald]

Post by d***@postmaster.co.uk
It's a difficult choice: simple outdoor
aerial (at loft height) or better aerial in the loft itself. Obviously
it's easier to put something in the loft

That's not a real choice.

A small antenna may work well indoors, while a larger one
likely will not. In other words, your reral choices are,
in order of worst to best, a small antenna indoors,
the small antenna outdoors, or a large antenna outdoors.

A large antenna indoors will likely .... not certainly but
likely ... not work better than a small antenna indoors,
unless you have a window to point it through.

Doug McDonald

[Marky P]

On Mon, 17 Jan 2005 17:43:31 -0000, "Mike Gilmour"

Post by Mike Gilmour

Post by d***@postmaster.co.uk
Appologies for the cross posting, but despite this being OT for three
of these groups, these are the groups where I know people can answer
this question!
Right, sad aerial spotting time...
Is this an FM aerial?
http://www.david.robinson.org/pics/aerial1.jpg
http://www.david.robinson.org/pics/aerial2.jpg
I've seen one like this (but about twice as long, hence twice as many
elements!!!) on top of a house in a village somewhere, but didn't have
my camera with me.
The example I've photographed is on the top of a hi-fi shop in Hitchin,
Herts, UK, but the only aerial that _they_ know is on their roof is "a
high gain digital TV aerial" (which this probably, unless DTT is still
on VHF in Hitchin!).
So what is this aerial, and where was it bought from? Can they still be
bought? What is the advantage, if any, over the standard folded dipole
and several elements which make up most directional FM aerials?
Cheers,
David.

For broadcast FM, I believe its a Galaxie Model G.17 with 10 reflectors,
cicular dipole and six directors. 74" long with a gain of 15.9 dB and 45 deg
acceptance angle. I have the G.20 above my roof which is 30" longer than the
G17 gives extra 2dB extra gain and 28 degree acceptance angle. Sourced mine
from Ron Smith Luton Beds UK. The reason for mine is a) I'm in the Scottish
Highlands b) it feeds a good tuner Magnum Dynalab 'Etude'. The advantage
for me is mainly gain & a good clean signal.
Hope this helps,
Mike

Would that shop be David Orton?

Marky P.

[Malcolm Stewart]

Post by d***@postmaster.co.uk
Is this an FM aerial?
http://www.david.robinson.org/pics/aerial1.jpg
http://www.david.robinson.org/pics/aerial2.jpg
So what is this aerial, and where was it bought from? Can they still be
bought? What is the advantage, if any, over the standard folded dipole
and several elements which make up most directional FM aerials?
Cheers,
David.

Looks just like mine. It's an FM aerial and I bought it from R Smith in
Luton some years ago. (and you'll see one on my previous house in Rowstock
Lane, Colney Heath.) Needs a strong mast when the wind blows - 2" steel
does the job.
Will be using it later this evening when R3 is broadcasting Das Rheingold.

[Andereida]

Post by Malcolm Stewart
snip
Will be using it later this evening when R3 is broadcasting Das Rheingold.

Danke schöne for the reminder, Malcolm. Nearly missed it!!

Andereida

[John Porcella]

Post by d***@postmaster.co.uk
Appologies for the cross posting, but despite this being OT for three
of these groups, these are the groups where I know people can answer
this question!
Right, sad aerial spotting time...
Is this an FM aerial?
http://www.david.robinson.org/pics/aerial1.jpg

It looks like a TV aerial to me, and what an ugly one at that!

[Marky P]

On Mon, 17 Jan 2005 18:06:11 +0000 (UTC), "John Porcella"

Post by John Porcella

Post by d***@postmaster.co.uk
Appologies for the cross posting, but despite this being OT for three
of these groups, these are the groups where I know people can answer
this question!
Right, sad aerial spotting time...
Is this an FM aerial?
http://www.david.robinson.org/pics/aerial1.jpg

It looks like a TV aerial to me, and what an ugly one at that!

Not exactly pretty beasts, are they? But it's definitely a Galaxie
G17 FM aerial from Ron Smith of Luton. I had the G26 which was the
biggest one he produced on a regular basis. G29 & G32 were available
by special order. Due to cracks appearing in my gable wall, the whole
thing eventually had to come down. I now have a single dipole!

Marky P.

[tony sayer]

Post by d***@postmaster.co.uk
Appologies for the cross posting, but despite this being OT for three
of these groups, these are the groups where I know people can answer
this question!
Right, sad aerial spotting time...
Is this an FM aerial?
http://www.david.robinson.org/pics/aerial1.jpg
http://www.david.robinson.org/pics/aerial2.jpg
I've seen one like this (but about twice as long, hence twice as many
elements!!!) on top of a house in a village somewhere, but didn't have
my camera with me.
The example I've photographed is on the top of a hi-fi shop in Hitchin,
Herts, UK, but the only aerial that _they_ know is on their roof is "a
high gain digital TV aerial" (which this probably, unless DTT is still
on VHF in Hitchin!).
So what is this aerial, and where was it bought from? Can they still be
bought? What is the advantage, if any, over the standard folded dipole
and several elements which make up most directional FM aerials?
Cheers,
David.

Thats one of Ron Smiths circular polarised jobbies.

Use to have one but I found a conventional Yagi worked just as well if
not a tad better, but this was a few years ago.

The windload on one of those is serious stuff;)...

And here they are in all their glory!, though some of their stuff looks
like it might require planning permission;)

http://anas.worldonline.es/ronsmith/main.htm

[DAB sounds worse than FM]

Post by tony sayer
And here they are in all their glory!, though some of their stuff
looks like it might require planning permission;)
http://anas.worldonline.es/ronsmith/main.htm

How much are they?

[Marky P]

On Mon, 17 Jan 2005 19:12:36 GMT, "DAB sounds worse than FM"

Post by DAB sounds worse than FM

Post by tony sayer
And here they are in all their glory!, though some of their stuff
looks like it might require planning permission;)
http://anas.worldonline.es/ronsmith/main.htm

How much are they?

When I bought my G26 back in 1991, the price was £180. And that was
just the aerial. They came & put it up on a 20 foot mast with a
rotator.

Marky P.

[informer]

Post by Marky P

Post by DAB sounds worse than FM
How much are they?

When I bought my G26 back in 1991, the price was £180. And that was
just the aerial. They came & put it up on a 20 foot mast with a
rotator.
Marky P.

With free digital radio on sky do we need these sort of aerials now apart
from picking up the local BBC station?

[Malcolm Stewart]

Post by informer

Post by Marky P

Post by DAB sounds worse than FM
How much are they?

When I bought my G26 back in 1991, the price was £180. And that was
just the aerial. They came & put it up on a 20 foot mast with a

rotator.

Post by informer

Post by Marky P
Marky P.

With free digital radio on sky do we need these sort of aerials now apart
from picking up the local BBC station?

I thought "Sky" had some form of entrance fee. Let me know if I'm wrong,
and how I can enjoy satellite carried "free" programmes without contributing
to BSB or similar.

[Mark Carver]

Post by Malcolm Stewart
I thought "Sky" had some form of entrance fee. Let me know if I'm wrong,
and how I can enjoy satellite carried "free" programmes without contributing
to BSB or similar.

Almost every radio station on Sky's platform is unencrypted. Therefore
you can simply purchase a second hand Sky box on EBay, stick up a dish,
and away you go. Better still, get any non Sky satellite receiver and
use that instead, or get a DVB-S card for your PC and receive that way.

Have a look at the Sky Digital FAQ: http://tinyurl.com/6u4p9

[Richard L]

Post by Mark Carver

Post by Malcolm Stewart
I thought "Sky" had some form of entrance fee. Let me know if I'm wrong,
and how I can enjoy satellite carried "free" programmes without contributing
to BSB or similar.

Almost every radio station on Sky's platform is unencrypted. Therefore
you can simply purchase a second hand Sky box on EBay, stick up a dish,
and away you go. Better still, get any non Sky satellite receiver and
use that instead, or get a DVB-S card for your PC and receive that way.

Non-Sky satellite receivers are readily available in the UK from
specialist dealers -- including online ones, of course. But in
addition to the UK radio services, there's a vast choice of
satellite services from stations all over Europe and beyond. If
you want to explore these, Malcolm, you're better off with
something other than a Sky box -- Sky's receivers can't really
handle more than the one satellite.

[tony sayer]

Post by Marky P

Post by informer

Post by Marky P

Post by DAB sounds worse than FM
How much are they?

When I bought my G26 back in 1991, the price was £180. And that was
just the aerial. They came & put it up on a 20 foot mast with a

rotator.

Post by informer

Post by Marky P
Marky P.

With free digital radio on sky do we need these sort of aerials now apart
from picking up the local BBC station?

I thought "Sky" had some form of entrance fee. Let me know if I'm wrong,
and how I can enjoy satellite carried "free" programmes without contributing
to BSB or similar.

A standard digital satellite receiver, not a sky box, will bring all
that is unencrypted on the "Sky" or rather ASTRA system.

Have a look through this list and you can see what's clear and what's
not.

http://www.lyngsat.com/28east.html

and from across the channel;)

http://www.lyngsat.com/astra19.html

and

http://www.lyngsat.com/hotbird.html

the channels with a beige coloured background are the free to
view/listen ones.

A standard digital sat receiver can be had for less that 100 quid and a
dish and LNB aren't that expensive either...

[DAB sounds worse than FM]

Post by Malcolm Stewart

Post by informer

Post by Marky P

Post by DAB sounds worse than FM
How much are they?

When I bought my G26 back in 1991, the price was £180. And that was
just the aerial. They came & put it up on a 20 foot mast with a
rotator. Marky P.

With free digital radio on sky do we need these sort of aerials now
apart from picking up the local BBC station?

I thought "Sky" had some form of entrance fee. Let me know if I'm
wrong, and how I can enjoy satellite carried "free" programmes
without contributing to BSB or similar.

This page gives more information about it and a list of free-to-air TV
channels and radio stations:

http://www.wickonline.com/fta.htm

and the bit rates are significantly higher than on DAB:

http://www.digitalradiotech.co.uk/index.htm#bit_rate_table

so the audio quality will be higher than on DAB on the stations that use
lower bit rates.

And I've listed some suitable receivers and other equipment on here:

http://www.digitalradiotech.co.uk/dsat_rx.htm

Use S/PDIF to connect from the receiver to your hi-fi system if
possible.

[DAB sounds worse than FM]

Post by Marky P
On Mon, 17 Jan 2005 19:12:36 GMT, "DAB sounds worse than FM"

Post by DAB sounds worse than FM

Post by tony sayer
And here they are in all their glory!, though some of their stuff
looks like it might require planning permission;)
http://anas.worldonline.es/ronsmith/main.htm

How much are they?

When I bought my G26 back in 1991, the price was £180. And that was
just the aerial. They came & put it up on a 20 foot mast with a
rotator.

Any idea approx. how much they cost nowadays?

[David W.E. Roberts]

<snip>

Post by tony sayer
Use to have one but I found a conventional Yagi worked just as well if
not a tad better, but this was a few years ago.
The windload on one of those is serious stuff;)...
And here they are in all their glory!, though some of their stuff looks
like it might require planning permission;)
http://anas.worldonline.es/ronsmith/main.htm
--
Tony Sayer

So no Wideband or Group E then :-(

[Mike Gilmour]

Post by tony sayer

[clip[

Thats one of Ron Smiths circular polarised jobbies.
Use to have one but I found a conventional Yagi worked just as well if
not a tad better, but this was a few years ago.
The windload on one of those is serious stuff;)...

The G17 has a windload of 50lbs at 100mph but the G23 gets quite serious at
72lbs

Post by tony sayer
And here they are in all their glory!, though some of their stuff looks
like it might require planning permission;)
http://anas.worldonline.es/ronsmith/main.htm
--
Tony Sayer

[Neil]

I used to own a Galaxie 17, later upgraded to a 23. Unless Ron Smith has
re-designed these since 1997, I must say their performance above 104 MHz is
for one of a better word 'sh*te'. Granted, when he designed them the FM band
only extended to 105 MHz but these days the 105-108 sub-band is heavily
populated with stations and the performance is pretty poor with a 4-6dB roll
off between 104 and 106 MHz.

Between 90 and 101 MHz, yep, great antennas but the gain across the band
isn't broad enough for my liking. As for the 'reducing multipath' bit which
he quoted in his catalogue at the time, well I never experienced more
multipath on strong stations (eg Holme Moss) than when using my Galaxie.
Like previously mentioned by someone else, windloading is also a problem so
a sturdy heavy duty rotator is required.

I'm using a Triax FM8S these days, good gain between 90 and 107 with about a
1-2dB rolloff at the edges. Does anyone have much experience with Ron
Smith's UHF Yagis?

Interestingly, a friend of mine in the North Midlands has just ordered a
Winegard FM antenna from the US, the gain is pretty impressive and flat
across Band II as well. Anyone had any experiences with one of these?
http://www.lashen.com/vendors/winegard/pdf/hd6065p.pdf
--
Neil
(Manchester, UK)

Post by Mike Gilmour

Post by tony sayer

[clip[

Thats one of Ron Smiths circular polarised jobbies.
Use to have one but I found a conventional Yagi worked just as well if
not a tad better, but this was a few years ago.
The windload on one of those is serious stuff;)...

The G17 has a windload of 50lbs at 100mph but the G23 gets quite serious
at 72lbs

Post by tony sayer
And here they are in all their glory!, though some of their stuff looks
like it might require planning permission;)
http://anas.worldonline.es/ronsmith/main.htm
--
Tony Sayer

[Mike Gilmour]

Post by Neil
I used to own a Galaxie 17, later upgraded to a 23. Unless Ron Smith has
re-designed these since 1997, I must say their performance above 104 MHz is
for one of a better word 'sh*te'. Granted, when he designed them the FM
band only extended to 105 MHz but these days the 105-108 sub-band is
heavily populated with stations and the performance is pretty poor with a
4-6dB roll off between 104 and 106 MHz.

The centre frequency of most of the models is 93.0 MHz but if you wanted
good performance above 104 MHz then maybe a GTE model may have suited you
better whose centre frequency is 102 MHz, available on the 17, 20 & 23
models.

Mike

[tony sayer]

Post by Mike Gilmour

Post by Neil
I used to own a Galaxie 17, later upgraded to a 23. Unless Ron Smith has
re-designed these since 1997, I must say their performance above 104 MHz is
for one of a better word 'sh*te'. Granted, when he designed them the FM
band only extended to 105 MHz but these days the 105-108 sub-band is
heavily populated with stations and the performance is pretty poor with a
4-6dB roll off between 104 and 106 MHz.

The centre frequency of most of the models is 93.0 MHz but if you wanted
good performance above 104 MHz then maybe a GTE model may have suited you
better whose centre frequency is 102 MHz, available on the 17, 20 & 23
models.
Mike

As much as anyone would like to try the multi element Yagi array is a
fairly narrowband device, and I don't know of anyone who's successfully
changed that without substantially reducing the gain.

So no surprise really....

[Marky P]

On Tue, 18 Jan 2005 09:42:25 -0000, "Mike Gilmour"

Post by Mike Gilmour

Post by Neil
I used to own a Galaxie 17, later upgraded to a 23. Unless Ron Smith has
re-designed these since 1997, I must say their performance above 104 MHz is
for one of a better word 'sh*te'. Granted, when he designed them the FM
band only extended to 105 MHz but these days the 105-108 sub-band is
heavily populated with stations and the performance is pretty poor with a
4-6dB roll off between 104 and 106 MHz.

The centre frequency of most of the models is 93.0 MHz but if you wanted
good performance above 104 MHz then maybe a GTE model may have suited you
better whose centre frequency is 102 MHz, available on the 17, 20 & 23
models.
Mike

My G23 had a centre freq of 95 MHz for some reason. Apparently it was
a custom buit effort that someone didn't want. At that time, I use to
listen to Capital FM on 95.8, so it was perfect, & also had better
gain up the top end of the band.

Marky P.

[Richard Fry]

Post by tony sayer
Thats one of Ron Smiths circular polarised jobbies.

____________________

Although one structural shape in the aerial is roughly circular, this aerial
is linearly polarised.

An aerial element in the form of a small loop* is not circularly polarised;
it is linearly polarised with its peak gain in the two directions normal to
the plane of the loop (see Kraus, 3rd Edition, table 6-2). The presence of
the parasitic elements in this array -- all in the same plane -- will
remove some of the ambiguity from the pattern of the loop, and increase the
peak gain of the array.

Of course, the polarisation plane of the array will be the same as the
physical orientation in which its elements are mounted. But it will be
linearly polarised, not circularly polarised.

Other designs are needed for true circular polarisation, some of which can
be seen in the papers at the website linked below.

*where loop circumference is ~ one wavelength

RF

Visit http://rfry.org for FM transmission system papers.

[Googolplex]

Post by d***@postmaster.co.uk
Appologies for the cross posting, but despite this being OT for three
of these groups, these are the groups where I know people can answer
this question!
Right, sad aerial spotting time...
Is this an FM aerial?
http://www.david.robinson.org/pics/aerial1.jpg
http://www.david.robinson.org/pics/aerial2.jpg

There's one of those (but longer) in a house in the next village from me...

[Jules]

It 'poses' as one...
http://anas.worldonline.es/ronsmith/main.htm