It is too difficult for me to describe the FM antenna, I do know they
are the nasty ones you don't want to sit on.
I will find a picture so I can describe it better.
But anyway, if they are circular polarized, (thinking point light source
in my head) then I will not have any quiet spots.
I tried shielding the antenna with the steel top off a 55 gallon drum
while a co worker watched the signal, no difference.
I still think this was not too stupid an approach, since fm will not
bend too well around a corner.
It has been suggested that I mount the antenna/radio inside a parabolic
dish. Lots of problems with that.....
But, what if I used a dish that has the extended walls, I mean like a
cup with a parabolic bottom? I see them laying around all over the
place. I don't think I need a big one.
Btw, although I am sure our building is full of FM, I know the problem
is up on the tower, because like I said, our long shot is beautiful.
Will post again later with more details on the FM antenna.
Cary Todd Gooch
RF Engineer
New Roads Telecom
(479) 494-0300 X211
-----Original Message-----
From: Daron J. Wilson [mailto:daron@wilson.org]
Sent: Sunday, September 10, 2006 11:22 AM
To: 'CARY GOOCH'; towertalk@contesting.com
Subject: RE: [TowerTalk] Nasty RF Problem. Advice Please
Wow, lots to comment on.
This is an increasing problem with unlicensed and even licensed gear
where
the radio is so buried in the electronics there is little if any
troubleshooting one can do. Very frustrating, trying to guess if it is
just
RF overload or some problem that is somewhat easily corrected.
IMHO, much of that gear isn't going to hold up in a high RF site anyway,
it's just not designed for that. I've seen quite a bit of this concern
on
sites.
You might be able to find a lower RF field behind or below the broadcast
antenna, but since that stuff is circularly polarized, and with that
much
power, you will have RF almost everywhere. You might be able to measure
the
RF field and find a quieter spot. One thing would be to take two radios
and
shoot back and forth just up on the hill where the tower is, in the RF
environment. Crank the power down, make sure they will work at all in
that
much RF before you separate the radios.
In order to know the pattern of the FM antenna, you'll need to provide a
good description, find the manufacturer and get some plots. Generally,
they
are stacked elements which provides the gain, but there are numerous
different designs.
Good Luck!
Daron Wilson, RCDD
N7HQR
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of CARY GOOCH
> Sent: Sunday, September 10, 2006 8:26 AM
> To: towertalk@contesting.com
> Subject: [TowerTalk] Nasty RF Problem. Advice Please
>
> We have an 80ft tower on which reside two tower mount Airstream 5.8GHz
> Radios. One fires through a 6ft parabolic 27 miles clean as a whistle.
>
> The other has an integrated antenna, 2 mile shot and taking so much
> interference from a 3KW FM Stereo antenna 40 feet higher up the tower
> that I can not even log into it (power over Ethernet, shielded cable
> with drain wire.
>
> I have moved the antenna, changed polarity, upped the transmit
distance
> setting, everything I can think of. The only time I do not get RF and
> Ethernet frame drops (sometimes 90 percent) is when I have the FM
> transmitter turned off.
>
> We also have Nivini (spelling) gear in the building at 2.4GHz, and
> though it is working well enough, their tech says they are getting
> significant interference as well.
>
> Barring the obvious (move a whole lot of gear to another tower, time
and
> money) is there something else I might do?
>
> Now I don't know what an FM Stereo radiation pattern looks like, but
> when I woke up this morning it occurred to me that if I had my
> radio/antenna setup DIRECTLY below the FM setup, that I might have
found
> a null spot in the FM pattern? I think that if I can just clean up the
> signal in this one antenna that we can live with the interference on
the
> rest of the gear.
>
> But I don't know if there IS a null spot, or even if it would matter.
>
> Since my 27 mile shot with parabolic antennas is so clean, I know that
> is an option, but these integrated antenna radios do not have options
> for external antennas. New airstream radios for this company are a
> rather significant investment.
>
> What can I do?
>
> Advise please. If I have not been clear on any points then ask me to
> elaborate. I am just getting some coffee.
>
> Best regards,
>
> Cary Todd Gooch
> RF Engineer
> New Roads Telecom
> (479) 494-0300 X211
>
>
> _______________________________________________
>
>
>
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