On 1/13/2011 11:58 AM, John Geiger wrote:
> Hi Jim,
> Even with the digital TV switchover, aren't most people still using
> cable and getting signals the old fashion way? I know we are. We
> still have the same analog TV connected to the cable. I don't think
> the fact that the over the air TV signals are now digital has affected
> my house at all.
> If it is a pin 1 problem then it is interesting in that it only
> affects certain TV channels.
Pin 1 problems take many forms. One is at the point where the antenna
(or CATV coax) comes into the TV set or cable box. Another is a poor
shield connection anywhere in that path.. These errors couple RF into
the TV, or into the CATV equipment. Most of these have nothing to do
with the cleanliness of your transmitter. Now, if your transmitter IS
putting out trash, these errors can couple that trash into the TV system.
> I will check on other TVs in the house that have the VCR/DVD unit
> input through the coax jack. The one in the living room uses audio
> cables intstead.
The equipment where those cables connect nearly always have pin 1
problems on both ends. Pin 1 problems occur on ALL cables, not only
audio or RF cables. Most serial ports have pin 1 problems.
> Also found that for the shack TV, it will shut off if I do 100 watts
> on 6m with the beam pointed east. Rotate it west and the TV shows no
> interference. That is interesting since the beam sits almost directly
> above where the TV is.
I'd look for one of those wiring problems or CATV equipment in the east
direction from your beam. For example, if there's a bad F-connector,
the adjacent piece of coax will couple it into the coax, and from there
to CATV system and/or the TV. If the set goes blank, I'd guess that
it's front end is simply being overloaded. Lots of F-connectors that
LOOK good are actually BAD. When I moved to CA about 5 years ago, I was
hearing CATV leakage around 145.25. I reduced it a lot by replacing one
of my own cables that I'd crimped at least 10 years before with a new
cable using much higher quality Snap N Seal connectors. The fact that
some leakage remains simply indicates that there are almost certainly
more poorly crimped connectors in that system. Looking for that leakage
with a 2M talkie is a great way to find and fix this part of the
problem. That's how I did it -- the noise around 145.25 will be loudest
near each bad connector. And don't quit when you find one bad one --
keep looking. If there's one there can easily be more.
Another suggestion. All recent editions of the ARRL Handbook include a
chart showing the harmonic relationship between ham bands and TV
channels, and between the translated channels used on CATV systems.
Study that chart for 6M and the cable channels where you have interference.
> I received plenty of other emails from hams who run legal limit with
> no affects on their own TVs. I would assume that many of them would
> still have the crappy equipment (TVwise) that the rest of us do with
> their pin 1 problems. Wonder what I am doing wrong that they aren't.
It probably is not what you are doing wrong, but what various equipment
mfrs and CATV installers are doing wrong. :) Most RFI is coupled by
various cables acting as antennas. The locations of those cables with
respect to your antennas, the quality of those cables, and how those
cables are connected to equipment, has a lot to do with whether there
will be RFI in any given situation.
Study my RFI tutorial. http://audiosystemsgroup.com/RFI-Ham.pdf
73, Jim Brown K9YC
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