I suggested making a couple of quarter wave stub filters

http://www.wrightsaerials.tv/Resourc...terference.pdf
has a bit of info about this.

Bill

wrote
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.

On 20 Jan 2005 12:07:09 -0800,
wrote:

I suggested making a couple of quarter wave stub filters

http://www.wrightsaerials.tv/Resourc...terference.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

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


"Neil" wrote in message
...
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.

Arthur wrote:
On 20 Jan 2005 12:07:09 -0800, wrote:

I suggested making a couple of quarter wave stub filters

http://www.wrightsaerials.tv/Resourc...terference.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 :-)

In message .com
" wrote:

I suggested making a couple of quarter wave stub filters

http://www.wrightsaerials.tv/Resourc...terference.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 L.

Mark Carver wrote:

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?


--
Steve - www.digitalradiotech.co.uk - Digital Radio News & Info

Find the cheapest Freeview, DAB & MP3 Player Prices:
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http://www.digitalradiotech.co.uk/mp...e_capacity.htm

DAB sounds worse than FM wrote:
Mark Carver wrote:

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

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/Resourc...terference.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.

On Fri, 21 Jan 2005 07:39:48 -0000, Mark Carver
wrote:

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

In article , Arthur
writes
On Fri, 21 Jan 2005 07:39:48 -0000, Mark Carver
wrote:

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
--
Tony Sayer

Mark Carver wrote:
DAB sounds worse than FM wrote:
Mark Carver wrote:

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.


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/Resourc...terference.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?


--
Steve - www.digitalradiotech.co.uk - Digital Radio News & Info

Find the cheapest Freeview, DAB & MP3 Player Prices:
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http://www.digitalradiotech.co.uk/mp...e_capacity.htm

Arthur wrote:
On Fri, 21 Jan 2005 07:39:48 -0000, Mark Carver

wrote:
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.

On Fri, 21 Jan 2005 11:31:21 +0000, tony sayer wrote:

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

DAB sounds worse than FM wrote:


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 ?

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 ?

On 21 Jan 2005 04:33:27 -0800, "
wrote:

Arthur wrote:
On Fri, 21 Jan 2005 07:39:48 -0000, Mark Carver

wrote:
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.

Mark Carver wrote:
DAB sounds worse than FM wrote:


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.


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?


--
Steve - www.digitalradiotech.co.uk - Digital Radio News & Info

Find the cheapest Freeview, DAB & MP3 Player Prices:
http://www.digitalradiotech.co.uk/fr..._receivers.htm
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http://www.digitalradiotech.co.uk/mp...e_capacity.htm

DAB sounds worse than FM wrote:
Mark Carver wrote:

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.

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.

In message
"DAB sounds worse than FM" wrote:

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.

;-)

--
Richard L.

Mark Carver wrote:
DAB sounds worse than FM wrote:

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.


--
Steve - www.digitalradiotech.co.uk - Digital Radio News & Info

Find the cheapest Freeview, DAB & MP3 Player Prices:
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http://www.digitalradiotech.co.uk/da...tal_radios.htm
http://www.digitalradiotech.co.uk/mp...rs_1GB-5GB.htm
http://www.digitalradiotech.co.uk/mp...e_capacity.htm

wrote:
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...