On Fri, 10 Sep 2004 03:50:44 GMT, A-Tech hath writ:
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

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.

I think, as Roy suggested, that your best attack will be to aim
the antenna to provide the deepest null to the "... off-axis
stronger signal at 106.9MHz". Peaking the desired signal is
only a secondary goal here.

Don't spend a lot of Big Bucks trying to solve this problem.
Marvin's Law (Murphy's brother) says that once you _have_ put
considerable money, effort, and time into this, the station's
(new) owner will change the format to Country or Jesus.
(Now, How's *that* for provoking thread drift?)

gl es 73
Jonesy
--
| Marvin L Jones | jonz | W3DHJ | linux
| Gunnison, Colorado | @ | Jonesy | OS/2 __
| 7,703' -- 2,345m | config.com | DM68mn SK

On 10 Sep 2004 16:10:57 GMT, Allodoxaphobia wrote:

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

Hello Bryce,

I'm sure you're aware that these two frequencies are adjacent channels. The FCC
allocated channels such that adjacent channels stations would not be located in
the same geographical area, expressly fo the purpose of preventing such
interference. Obviously the two channels involved are not in the same area, and
it seems strange to me that you can even hear the station on 107.1 MHz.

I believe that your only hope is to orient your antenna to place the null in the
direction of the 106.9 station, as Roy suggested,, but I'm not sure that even
that will reduce the 106.9 station sufficiently to allow acceptable reception of
the 107.1 station. In addition, I firmly believe that attempting to filter out
an adjacent channel will be futile, and not worth the effort.

Walt, W2DU

"Walter Maxwell" wrote in message
...
On 10 Sep 2004 16:10:57 GMT, Allodoxaphobia wrote:

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

Hello Bryce,

I'm sure you're aware that these two frequencies are adjacent channels.
The FCC
allocated channels such that adjacent channels stations would not be
located in
the same geographical area, expressly fo the purpose of preventing such
interference. Obviously the two channels involved are not in the same
area, and
it seems strange to me that you can even hear the station on 107.1 MHz.
.....
Walt, W2DU

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.
--
Steve N, K,9;d, c. i My email has no u's.

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

"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