[amsat-bb] Re: 2 Meter TV Interference

Wed Dec 7 21:44:10 PST 2011

Charles,
Our Channels 8 & 10 moved the digital channel from UHF to VHF at the end of
the conversion period. Since they had to give up one channel and the
operating costs for the same coverage are considerably less on VHF it was a
easy decision to make. I doubt this is what FCC had in mind, but that is how
it worked out. 

UHF has less noise (Very little galactic noise) and significantly smaller
antennas,(shorter wavelength) making the UHF segment more desirable for
portable operations. Best policy is to use the VHF band for TV and save UHF
for other uses. 

Interesting enough a 5 Watt "S" Band link transmitter carries the video
signal to the local cable TV companies that serve 90% of the viewers. Only
10% receive their TV signals over the air!

That is how it is done in Southern California.

73,
Art KC6UQH  

-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of Charles Suprin
Sent: Wednesday, December 07, 2011 1:49 PM
To: Bob Bruninga
Cc: amsat-bb at amsat.org; Gordon JC Pearce
Subject: [amsat-bb] Re: 2 Meter TV Interference

I didn't think there were any vhf stations left. All the numbers on the
channels now are virtual. All the tv antenna plans are for uhf bands. A
quick look in the Boston market and the lowest channel is 19, channel
2 at 500MHz. Are there places that still use vhf?

Charles
On Dec 7, 2011 1:38 PM, "Bob Bruninga" <bruninga at usna.edu> wrote:

> 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
>
> -----Original Message-----
> From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
> Behalf Of Gordon JC Pearce
> Sent: Wednesday, December 07, 2011 3:02 AM
> To: amsat-bb at amsat.org
> Subject: [amsat-bb] Re: 2 Meter TV Interference
>
> On Tue, 6 Dec 2011 21:17:55 -0600
> Wyatt Dirks <wyattdirks at msn.com> wrote:
>
>
> > 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.The 1/4 wave is mounted permanently via a hole in the roof
> of
> my truck an the 1/2 wave is mounted on a mount opposite the factory
> installed FM/AM radio whip. It doesn't seem to matter what antenna I use
> for
> the problem to occur. Then I use either the arrow antenna or my cju for
the
> downlink.
>
> Use 5W into a hand-held Yagi.  You'll get far better results.
>
>
> > 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.
>
> What you want is a highpass filter that will lop off everything below
> 500MHz.  The chances are that your TX output is clean enough but the
little
> amplifier in the splitter for the TV is causing all sorts of intermod -
and
> probably covers from broadcast VHF radio to the top of the TV band.
>
> --
> Gordon JC Pearce MM0YEQ <gordonjcp at gjcp.net>
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