[amsat-bb] Re: 2 Meter TV Interference

i8cvs domenico.i8cvs at tin.it
Wed Dec 7 15:24:21 PST 2011

----- Original Message -----
From: "Bob Bruninga" <bruninga at usna.edu>
To: "'Gordon JC Pearce'" <gordonjcp at gjcp.net>; <amsat-bb at amsat.org>
Sent: Wednesday, December 07, 2011 7:24 PM
Subject: [amsat-bb] Re: 2 Meter TV Interference

> HPF above 500 MHz?  Then the TV would not be able to see anything but a
> few UHF channels.
> What is needed is a stub filter.  Just a piece of open ended coax 13" long
> "T"ed into the antenna lead....
> The 13" is about 66% of a quarter wave at 2 meters.
> Done
> Bob, WB4APR

Hi Bob, WB4APR

If the "open stub" is tuned to the 2 meters band and attached to the TV-set
of one's neighbour a reduction of the 2 m signals of  25 to 30 dB may be

At the same time all odd harmonics of the design frequency (3f, 5f, etc
will be attenuated as well.

Since the UHF amateur is particularly concerned with f and 3f  this "open
stub" is usefull as well when one transmit in 432-435 MHz

On the other side if the quality of the previously good and clear TV-picture
is reduced upon correct insertion of the "open 1/4 wave stub" one should
investigate whether 3f, 5f, or 7f fall into the television frequency band.
If this is the case it may become necessary to tune to a different TV
channel or turn the antenna to a different TV-station.

I have just received a suggestion from James VK6FJA that I agree
because of my previous experience in solving my TVI problems in
HF and VHF in my condo.

"Nothing can be done to the Tx, better to offer a working filter to the
Rx side! "


This 144 MHz Stop-Band TVI  Filter is based on a QST article found

VK6FJA says to me  "it works just fine - and it can be aligned without
the test gear, there's only 2 trimmers in it."

73" de

i8CVS Domenico

----- Original Message -----
From: "Wyatt Dirks" <wyattdirks at msn.com>
To: <amsat-bb at amsat.org>
Sent: Wednesday, December 07, 2011 4:17 AM
Subject: [amsat-bb] 2 Meter TV Interference
> Just recently I have been having troubles with a neighbor while I am
> working the FM satellites(SO-50 and AO-27). The setup I am currently using
> is my mobile setup because I am unable to put a base station up for many
> reasons. I am using a FT8900 with 50 watts out into a 1/4 wave or 1/2
> Larson mobile antenna.
> Today I had another local ham over at the request of the neighbor and his
> mobile Kenwood radio did the same thing to the neighbors tv when he
> transmitted on 2 meter with 50 watts out. He also recommended that they
> get a filter. I did not see the specs on the filter nor do I know what
> bandwidth it was for.
> If anyone has any ideas on what would solve this problem and could share
> that would be great.
> Catch you on the birds
> Wyatt AC0RA

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