Success likely in the null?
 

I'm trying to receive some a distant FM stations, but I have locals 0.1Mhz
away that block the desired station out. I could try to use a big gain
directional yagi, but perhaps the solution is to make use of a null.

Anyone know of any antenna system that would produce a real good null in
the FM band? Would that be to try for a cardoid pattern? Or is there
something better than that?


Detail:

Intended Coord.of Interfering Coord.of Angular
station + antenna station + antenna sep. of
Freq. Freq. stations
Mhz Mhz from my
QTH
-------------------------------------------------------
Scarboro' 00w24/ RadioAire 01w34/ 45
96.2 54n16 96.3 53n44 degrees

Bridlington 00w12/ Pulse FM 01w45/ 114
102.4 54n05 102.5 53n48 degrees

Whitby 00w36/ Sunrise Radio 01w45/ 75
103.1 54n29 103.2 53n50 degrees


As you see the seperation between the wanted stations and the interfering
stations range from appx.45 degrees to 114 degrees. Intefering stations are
always anticlockwise to the wanted station, but perhaps that makes no div.

BTW I think the Bridlington transmitter antenna coordinates are 00w12/54n05.
Wonder if anyone can confirm this.

Data obtained from:

http://www.ukwtv.de/fmlist/countries.html

Where Bridlington is on107.4 Mhz, which is now incorrect, because
Bridlington is on 102.4Mhz.

TIA.Rich.

On Sat, 14 Feb 2004 14:21:12 -0000, "Richard"
wrote:
Anyone know of any antenna system that would produce a real good null in
the FM band? Would that be to try for a cardoid pattern? Or is there
something better than that?

Hi Richard,

That would be useful (the cardioid) if the signal strengths are good
enough to follow the interfering signal down into the null. To put
the interfering signal into the null means degrading the other 10 or
more dB.

Otherwise, look for a yagi with about 30 degrees of beam width (in the
vertical polarization).

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Sat, 14 Feb 2004 14:21:12 -0000, "Richard"
wrote:
Anyone know of any antenna system that would produce a real good null in
the FM band? Would that be to try for a cardoid pattern? Or is there
something better than that?

Hi Richard,

That would be useful (the cardioid) if the signal strengths are good
enough to follow the interfering signal down into the null. To put
the interfering signal into the null means degrading the other 10 or
more dB.

Otherwise, look for a yagi with about 30 degrees of beam width (in the
vertical polarization).

Thing is, these stations would be quite weak, so I could do with gain, so
perhaps a good yagi is the way to go after all. .Like you say, rotate until
the offending station goes down in the null of the antenna.

I think also you are saying use vertical polarization, because that
orientation always produces the sharper pattern. I never thought about that.
I was though intending to mount vertically as it happens. Thanks.

On Sat, 14 Feb 2004 14:44:08 -0000, "Richard"
wrote:
I think also you are saying use vertical polarization, because that
orientation always produces the sharper pattern. I never thought about that.
I was though intending to mount vertically as it happens. Thanks.

Hi Richard,

I was careful to mention vertical polarization, because barring some
across-the-pond differences, that is what your broadcaster uses. If
you attempted to listen to them with horizontal polarized antennas,
you would suffer what is called "cross-polarization." The
consequences of this are signals that are down 20dB or more. If those
signals are circular polarized, then the vertical or horizontal would
work equally well (as long as that beam width was half the difference
of the two bearings).

73's
Richard Clark, KB7QHC

Richard Clark wrote:

Otherwise, look for a yagi with about 30 degrees of beam width (in the
vertical polarization).

Wow that would mean a large FM directional antenna would it not?

I'm looking at an 8 element, and the beamwidth is + - 21 degrees, that be 42
degrees of beam width. But, it's not clear whether that be horizontal or
vertical beamwidth, presumably horizontal. I'll have to check. Maybe an 8
element might have a 30 degree beamwidth in the vertical.

Hello,

A dipole mounted too close to a metal pole will cause a cardioid pattern.
The coordinates don't mean much to me, but a picture would with all the
station TXs and your marked on it .
The problem is, if you have a local 10K transmitter and try to null it out
in favour of a distant station, it will probably not work. Calculate the
loss of say 20 or 30dB to a local TX.
Buy a DAB instead (if you like MW sound quality as they TX in MONO). You
might hear the stations that way.

"Richard" wrote in message
...
I'm trying to receive some a distant FM stations, but I have locals
0.1Mhz
away that block the desired station out. I could try to use a big gain
directional yagi, but perhaps the solution is to make use of a null.

Anyone know of any antenna system that would produce a real good null in
the FM band? Would that be to try for a cardoid pattern? Or is there
something better than that?


Detail:

Intended Coord.of Interfering Coord.of Angular
station + antenna station + antenna sep. of
Freq. Freq. stations
Mhz Mhz from my

QTH
-------------------------------------------------------
Scarboro' 00w24/ RadioAire 01w34/ 45
96.2 54n16 96.3 53n44 degrees

Bridlington 00w12/ Pulse FM 01w45/ 114
102.4 54n05 102.5 53n48 degrees

Whitby 00w36/ Sunrise Radio 01w45/ 75
103.1 54n29 103.2 53n50 degrees


As you see the seperation between the wanted stations and the interfering
stations range from appx.45 degrees to 114 degrees. Intefering stations
are
always anticlockwise to the wanted station, but perhaps that makes no div.

BTW I think the Bridlington transmitter antenna coordinates are
00w12/54n05.
Wonder if anyone can confirm this.

Data obtained from:

http://www.ukwtv.de/fmlist/countries.html

Where Bridlington is on107.4 Mhz, which is now incorrect, because
Bridlington is on 102.4Mhz.

TIA.Rich.

Hi Richard,

Horizontal polarisation from UK TV/radio TXs seems to travel a lot further
on the same power than vertical. The same has been found over distances
using 2m/70cm.

"Richard Clark" wrote in message
...
On Sat, 14 Feb 2004 14:44:08 -0000, "Richard"
wrote:
I think also you are saying use vertical polarization, because that
orientation always produces the sharper pattern. I never thought about
that.
I was though intending to mount vertically as it happens. Thanks.

Hi Richard,

I was careful to mention vertical polarization, because barring some
across-the-pond differences, that is what your broadcaster uses. If
you attempted to listen to them with horizontal polarized antennas,
you would suffer what is called "cross-polarization." The
consequences of this are signals that are down 20dB or more. If those
signals are circular polarized, then the vertical or horizontal would
work equally well (as long as that beam width was half the difference
of the two bearings).

73's
Richard Clark, KB7QHC

Richard wrote:
"Anyone know of any antenna system that would produce a real good null
in the FM band?"

Direction finding relies on sharp nulls. The small loop works well with
vertically polarized ground waves, but small loops don`t work well in
nulling out horizintally polarized waves simultaneously with a null in
vertically polarized waves .

The lack of a simultaneous small loop null in both polarizations was the
cause for development of an improved Radio Direction Finding (RDF)
antenna, which was patented by F. Adcock in 1919. The story is found in
the 19th edition of the ARRL Antenna Book on page 14-5.

FM broadcasts typically contain both polarizations, so what`s needed is
an antenna which nulls out both polarizations.

The Adcock antenna has been found to prooduce good nulls under sky-wave
conditions (containing both polarizations) at HF when loops produced
poor nulls.

Instructions and directional patterns for the Adcock appear in the ARRL
book. All that`s necessary is to approximately scale the Adcock for the
frequency of the null.

With the interfering station in the null, the desired station may
capture the FM detector.

Best regards, Richard Harrison, KB5WZI

Richard wrote:
I'm trying to receive some a distant FM stations, but I have locals
0.1Mhz away that block the desired station out. I could try to use a big
gain directional yagi, but perhaps the solution is to make use of a null.

Anyone know of any antenna system that would produce a real good null in
the FM band? Would that be to try for a cardoid pattern? Or is there
something better than that?

I think these might provide a solution:

http://www.geocities.com/toddemslie/...ncellation.htm

http://www.anarc.org/wtfda/stagger.pdf

http://pages.cthome.net/fmdx/phase.html

Horizontally stacking yagi antennas will give you a deep null. The
horizontal distance determines where that null falls with respect to
the main beam of the pair. Cable tv systems sometimes employ this
method to get rid of an interfering station. You can probably find
some information as to spacing requirements in cable tv handbooks or
antenna manufacturers that supply antennas to them.

Horizontal stacking will give you a much sharper beam width than a
single yagi also.

Not sure of the polarization of the fm stations where you are but in
the US they all transmit both horizontal and vertical.

73
Gary K4FMX

On Sat, 14 Feb 2004 14:21:12 -0000, "Richard"
wrote:

I'm trying to receive some a distant FM stations, but I have locals 0.1Mhz
away that block the desired station out. I could try to use a big gain
directional yagi, but perhaps the solution is to make use of a null.

Anyone know of any antenna system that would produce a real good null in
the FM band? Would that be to try for a cardoid pattern? Or is there
something better than that?


Detail:

Intended Coord.of Interfering Coord.of Angular
station + antenna station + antenna sep. of
Freq. Freq. stations
Mhz Mhz from my
QTH
-------------------------------------------------------
Scarboro' 00w24/ RadioAire 01w34/ 45
96.2 54n16 96.3 53n44 degrees

Bridlington 00w12/ Pulse FM 01w45/ 114
102.4 54n05 102.5 53n48 degrees

Whitby 00w36/ Sunrise Radio 01w45/ 75
103.1 54n29 103.2 53n50 degrees


As you see the seperation between the wanted stations and the interfering
stations range from appx.45 degrees to 114 degrees. Intefering stations are
always anticlockwise to the wanted station, but perhaps that makes no div.

BTW I think the Bridlington transmitter antenna coordinates are 00w12/54n05.
Wonder if anyone can confirm this.

Data obtained from:

http://www.ukwtv.de/fmlist/countries.html

Where Bridlington is on107.4 Mhz, which is now incorrect, because
Bridlington is on 102.4Mhz.

TIA.Rich.

In article ,
"Richard" wrote:

I'm trying to receive some a distant FM stations, but I have locals 0.1Mhz
away that block the desired station out. I could try to use a big gain
directional yagi, but perhaps the solution is to make use of a null.

Putting the undesired signal in an antenna null is a great idea,
provided the undesired signal is coming from one direction only. If
there is multipath propagation, that may not be true. How are you going
to null out several different bounced versions of the signal
simultaneously?

In North America FM broadcast channels are spaced 200 kHz apart rather
than the 100 kHz spacing you indicate. But even then there can be
adjacent channel problems.

One signal which I would like to listen to comes from a low powered
repeater station (43 watts effective radiated power) on 91.1 MHz with
antenna at an altitude of 1316 m and about 80 km south of where I live;
there are a few low hills in the way so the path is not line of sight
but the signal strength, in the absence of interference, is quite
adequate. High altitude can help make up for low power.

There are two interfering signals. One is on 90.9 MHz, has antenna at
about 800 m altitude, has much higher power, and is less than 20 km away
but is behind a nearby low ridge so that the signal is diffracted and
also arrives from lots of directions due to bounces. The other
interfering signal is on 91.3 MHz, is of even higher power than the
nearby one, has a much lower antenna since it is located on an island
with no nearby high points, and is located slightly closer than the
desired station. It too arrives from lots of directions at once.

I used to be able to receive the 91.1 MHz station quite well, even when
using a whip antenna on an ordinary kitchen radio. (Actually it was on
91.3 MHz then; it moved 200 kHz lower when the 91.3 MHz station came on
the air.) Reception using a good Yagi antenna connected to an excellent
stereo FM tuner became difficult when the higher frequency one came on
the air, and became impossible when the nearby lower frequency one came
on the air. So now I listen to the main transmitter on 88.5 MHz, perhaps
200 km away, whose repeater I used to receive very well, but I listen to
it via our cable connection. I believe that the cable company's
reception antennas are up on one of the mountains to the north where the
nearby interfering station's antenna is located. I don't know whether
they actually pick up the 88.5 MHz main transmitter signal or the closer
91.1 MHz low powered repeater signal, but up where their receiving
antenna are, both paths should be line of sight or nearly so. When I am
in my car, using an extremely sensitive and quite selective Sony
receiver, reception of the repeater station becomes possible when I
drive perhaps 20 km closer to it than my home, but by that time the main
station's signal is also strong enough for quite acceptable listening
quality.

David, ex-W8EZE

--
David Ryeburn

To send e-mail, use "ca" instead of "caz".