On Fri, 10 Sep 2004 13:38:34 -0500, "Steve Nosko"
wrote:

When you are BETWEEN markets, this is common. Or, if you want to listen
to a distant station and the wrong one is close. I'm equi-distant from
Chicago, Milwaukee and Rockford and have this problem hearing WDCB 90.9,
west of CHi-town with WHAD 90.7, S-W of Milwaukee pounding in. They're in
different markets.

This was discussed not to long ago here. A notch in the antenna pattern
is not too difficult. Two vertical dipoles spaced (about) a half wave and
fed with the proper feed line so they are 180 degrees out from each other,
can make a nice null - actually two. They are perpendicular to the plane of
the antennas. I'd have to sit and tinker to remember the feed system, but
there has to be 1/2 wave more feed line in one dipole, compared to the
other.
It is also possible to do the same thing and get a one notch pattern
(cardioid). If I recall, the antennas are spaced 1/4 wave apart and the
feed is 3/4 wave of feed line between them. Again, the receiver simply
connects to one of them and the null is off one end.

Yeah, Steve, but isn't FM broadcast wirh horizontal polarfization? With vertical
dipoles the only signal you'll receive is from reflect;ions off objects such as
buildings. What kind of reflection coefficient would one expect ? Enough for a
good signal?

Walt

{original msg at end}
Firstly, let me thank you one and all for your responses!!

Also, I did not clearly define the antenna which is a
multi-element yagi of Winegard design - a "standard"
consumer product - and roof mounted.

In addition, I have MapQuested
the two transmitters and find that the interfering
radiation comes from behind, about 25degrees
off axis. This signal originates about 30miles behind
me and the desired signal is about 55miles in front.

Richard Clark took me along the method that I had
tried - and that I have had no success with.

Dale W4OP points out that this type filter,
at these frequencies, have almost no effect - boo!

Roy Lewallen, W7EL, concurred with Dale and suggested
a "phased array" design. Unfortunately, this is beyond
my capabilities. Roy and Walt, W2DU, both agreed that
using "null tuning" might help. Roy also suggested a "choke"
for the feedline to reduce feedline pickup. - But it seems to me
that 95% shielded 75ohm coax should not be a
contributing factor.

Bob suggested that I call the offending station - I did that
but I have to wait until Monday to speak with their
engineer - boo.

Crazy George alluded to an article about constructing
a "stacked yagi" - interesting and within reasonable
economics - but no details or source for details. Ah well.
He also brought back into my memory EagleFilters
which I have used in a cable television distribution
setting. I'm looking them up on the Internet now.

"jqo" suggested shielding from the bad signal, a strategy
I have successfully used in C-Band-satellite-receiving-antenna
placements but....on my rooftop? Also, he suggested a tuner
with better selectivity. I agree and am on eBay looking for
a better unit than the Cadet AM/FM Radio card that is
installed in my PC and connected to the outdoor antenna.

BTW, "jqo", Q, in a filter, means "quality" but is really a
figure of merit that refers to width of the 3db down points
(in frequency) and the total energy removed. High Q filters
have narrow -3db points and suck out LOTS of energy.

Jonesy suggests that if I just wait, like the weather, the station
will change format and I'll no longer care to solve this!!

Thanks all - any additional comments are most welcome.

....Bryce


"A-Tech" wrote in message
news
Living as I do in a suburban area, I use an FM antenna to draw the
stations
located in a certain vector from me. A station of interest is located at
107.1MHz but
is interfered with by an off-axis stronger signal at 106.9MHz

The FM antenna has a "standard" 300ohm screw connection for the lead-in
(to
which I connect a 300/75 xfmr and use coax down).

I would appreciate anyone's help in designing and implementing a notch
filter that would suck out a major part of the interfering energy.
It seemed to me that a reasonable attempt would be to use a piece of
300ohm
flat-lead and short it at an appropriate distance from the screw-terminals
of the antenna. None
of my attempts have yielded any observable improvements. It may be that
the filter must be
"deeper" (higher Q?) than what my attempts provide.

"Walter Maxwell" wrote in message
...
On Fri, 10 Sep 2004 13:38:34 -0500, "Steve Nosko"
wrote:

When you are BETWEEN markets, this is common. Or, if you want to
listen
to a distant station and the wrong one is close. I'm equi-distant from
Chicago, Milwaukee and Rockford and have this problem hearing WDCB 90.9,
west of CHi-town with WHAD 90.7, S-W of Milwaukee pounding in. They're
in
different markets.

This was discussed not to long ago here. A notch in the antenna
pattern
is not too difficult. Two vertical dipoles spaced (about) a half wave
and
fed with the proper feed line so they are 180 degrees out from each
other,
can make a nice null - actually two. They are perpendicular to the plane
of
the antennas. I'd have to sit and tinker to remember the feed system,
but
there has to be 1/2 wave more feed line in one dipole, compared to the
other.
It is also possible to do the same thing and get a one notch pattern
(cardioid). If I recall, the antennas are spaced 1/4 wave apart and the
feed is 3/4 wave of feed line between them. Again, the receiver simply
connects to one of them and the null is off one end.

Yeah, Steve, but isn't FM broadcast wirh horizontal polarfization? With
vertical
dipoles the only signal you'll receive is from reflect;ions off objects
such as
buildings. What kind of reflection coefficient would one expect ? Enough
for a
good signal?

Walt

To the best of my knowledge- commercial FM broadcast has transmitted on both
V and H for many years- how else would a vertical whip on an automobile
receive FM?

Dale W4OP

On Fri, 10 Sep 2004 23:18:13 GMT, "Dale Parfitt" wrote:


"Walter Maxwell" wrote in message
.. .
On Fri, 10 Sep 2004 13:38:34 -0500, "Steve Nosko"
wrote:

When you are BETWEEN markets, this is common. Or, if you want to
listen
to a distant station and the wrong one is close. I'm equi-distant from
Chicago, Milwaukee and Rockford and have this problem hearing WDCB 90.9,
west of CHi-town with WHAD 90.7, S-W of Milwaukee pounding in. They're
in
different markets.

This was discussed not to long ago here. A notch in the antenna
pattern
is not too difficult. Two vertical dipoles spaced (about) a half wave
and
fed with the proper feed line so they are 180 degrees out from each
other,
can make a nice null - actually two. They are perpendicular to the plane
of
the antennas. I'd have to sit and tinker to remember the feed system,
but
there has to be 1/2 wave more feed line in one dipole, compared to the
other.
It is also possible to do the same thing and get a one notch pattern
(cardioid). If I recall, the antennas are spaced 1/4 wave apart and the
feed is 3/4 wave of feed line between them. Again, the receiver simply
connects to one of them and the null is off one end.

Yeah, Steve, but isn't FM broadcast wirh horizontal polarfization? With
vertical
dipoles the only signal you'll receive is from reflect;ions off objects
such as
buildings. What kind of reflection coefficient would one expect ? Enough
for a
good signal?

Walt

To the best of my knowledge- commercial FM broadcast has transmitted on both
V and H for many years- how else would a vertical whip on an automobile
receive FM?

Dale W4OP

You're right, Dale, my age and ignorance are showing.

Walt

A-Tech wrote:
. . .
Roy Lewallen, W7EL, concurred with Dale and suggested
a "phased array" design. Unfortunately, this is beyond
my capabilities. Roy and Walt, W2DU, both agreed that
using "null tuning" might help. Roy also suggested a "choke"
for the feedline to reduce feedline pickup. - But it seems to me
that 95% shielded 75ohm coax should not be a
contributing factor.
. . .

With the added knowledge of your antenna and your technical
capabilities, the approach I'd encourage you to try is to simply turn
your antenna while listening. It might not take much turning to get the
interfering signal into a null, leaving the desired signal close enough
to the peak of the front directional lobe to be strong enough.

The problem with feedline pickup has nothing to do with the shielding,
it's caused by current on the outside of the shield. But it's not likely
to be a concern with your commercial antenna and coax because of the way
these antennas are typically fed.

Roy Lewallen, W7EL

A company in FL - well, they might have been blown away by now - called
something like Pizio Technologies makes VHF bandpass filters from "crystal"
elements. Such filters are capable of rejecting adjacent channels in the
150 MHz range and are needed in some cities if you have to put a receiver
downtown.
As Dale points out, it takes a serious filter indeed to perform what you
wish such a filter to perform. On the other hand, I have deliberately tuned
some higher end FM broadcast receivers to a weak adjacent station in the
presence of a fairly strong station to find a bit better than mediocre
performance. Some receivers have much better filtering than other
receivers.
So, as another summery: rotate antenna for best SNR; get a receiver
with better filtering; and consider a special-made crystal filter if you
still have a problem. 73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Dale Parfitt" wrote in message
news:_X90d.8722$Va5.8116@trnddc01...


Unfortunately, you will find that the -3dB BW of a single stub is in the
neighborhood of 5% or 5MHz at your frequency of interest. The
discrimination between your desired and undsired channels will be
negligible.
We manufacture a line of small multiple cavity symmetrical and
asymmetrical
notch filters- getting under 0.5% BW with small topology filters is nearly
impossible at VHF.

Dale W4OP

"J. Mc Laughlin" wrote in message
...
A company in FL - well, they might have been blown away by now - called
something like Pizio Technologies makes VHF bandpass filters from
"crystal"
elements. Such filters are capable of rejecting adjacent channels in the
150 MHz range and are needed in some cities if you have to put a receiver
downtown.
As Dale points out, it takes a serious filter indeed to perform what
you
wish such a filter to perform. On the other hand, I have deliberately
tuned
some higher end FM broadcast receivers to a weak adjacent station in the
presence of a fairly strong station to find a bit better than mediocre
performance. Some receivers have much better filtering than other
receivers.
So, as another summery: rotate antenna for best SNR; get a receiver
with better filtering; and consider a special-made crystal filter if you
still have a problem. 73 Mac N8TT

PTI is definitely still in business and are very capable of building such a
filter- unfortunately in small quantities they are cost prohibitive.

Dale W4OP

"A-Tech" wrote in message
news
Hi,

I am a newbie here and have just dropped in to ask a single technical
question.



Try a receiver with decent IF filters. Unfortunately, this might be
hard to do in this day and age, but at one time companies
were using crystal filters in the IF stages that offered some
decent adjacent channel rejection.

Pete

" Uncle Peter" wrote in message
news:CbE0d.138$iK2.93@lakeread08...

"
Try a receiver with decent IF filters. Unfortunately, this might be
hard to do in this day and age, but at one time companies
were using crystal filters in the IF stages that offered some
decent adjacent channel rejection.

Pete


I should add other than phased stacked antennas to null
the unwanted station, there is really no practical filter you
can use to notch an adjacent FM channel. A custom
crystal filter might do it, but that's many hundreds of
dollars. It's far easier and cheaper to do this sort of
filtering at the first IF. It might be easier to retrofit the
receiver with a good IF filter as compared to trying to
notch the undesired signal or bandpass the desired
signals at the operating frequencies.

Pete

"A-Tech" wrote in message
news
Hi,

I am a newbie here and have just dropped in to ask a single technical
question.

Living as I do in a suburban area, I use an FM antenna to draw the
stations
located in
a certain vector from me. A station of interest is located at 107.1MHz
but
is interfered with by an off-axis stronger signal at 106.9MHz

Hi Bryce,

you can try phase cancellation technique as described at
http://www.geocities.com/toddemslie/...ncellation.htm

Good luck!

Mario 9A4DE