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.