hey guys
while working on 6 meters tonight i got a knock on my door and the guy
said i was getting into his Satellite TV his TV is on channel 4 and his
Dish was Professionally installed so could someone let me know what i
can do to stop this?

i am unfamilar with sat TV and dont know how to cure this issue
so any info would be a big help

There could be two sorts of TVI he might be experiencing, with a
number of different causes.

The actual satellite TV system (I'm assuming it's Dish Network or
DirecTV, rather than an analog Big Ugly Dish) is using digital
MPEG-2 video compression. Interference with the actual digital
signals themselves would probably result in the image on the screen
breaking up into square or rectangular "macroblocks", freezing,
blanking out, and/or the satellite receiver putting up a splash-screen
saying "Looking for satellite signal".

If this is the problem, you'd probably be dealing with a high level of
RF current on his receiver-to-dish coax, or RF getting into the
receiver itself via the satellite cable, power cord, or the cable to
the TV. The way to deal with this would probably be to add
common-mode chokes - toroids, or clamp-on two-part beads - to all of
these wires. Chokes or beads on the satellite cable should be placed
at the receiver, at the dish (right by the LNB), and probably at a few
other places along the feedline.

It's more likely, though, that the RF is interfering with the
modulated (channel 4) signal from the satellite receiver to the TV
set. This wouldn't cause the signal to macroblock or freeze -
instead, you'd see analog noise on the screen, "herringbones", and
possibly a squawking sound in the audio. He might be hearing your
side of the QSO, and be disconcerted at hearing Donald Duck even when
tuned to a non-Disney channel.

This sort of interference might be the result of one of two sorts of
problems:

- Harmonics. Channel 4 is at 66 - 72 MHz. The 6-meter band is 50 -
54 MHz. As there's no simple harmonic relationship there, it's
probably not what's happening.

- Fundamental overload. It's quite common for a strong RF signal to
overload the NTSC tuner in a television - the tuner begins to react
to signals which lie outside of the bandwidth of the station it's
tuned to. This tends to happen because the RF front end
transistors are hit with such a strong signal that they begin
"clipping", or at least suffering from severe intermodulation.

The TV sets in our house can react to as little as 5 watts of
2-meter power from any of several different radios, and I'm going
to have to install a notch filter to restore domestic tranquility.

I'd guess that fundamental overload is more likely the problem. Your
6-meter signal is getting into the coax (or other cable) between his
satellite receiver and his TV set, and is overloading the tuner.

The good news (I suppose) is that if this is the problem, you are very
probably _not_ legally obligated to fix it. The FCC says that this
sort of thing is the fault of the receiving equipment (which has
inadequate shielding and filtering), rather than the transmitting
equipment (as long as it's transmitting signals only in the authorized
amateur bands, at legal power levels).

In practice, though, and for good-neighbor reasons, it's often best if
you help advise the TV owner as to how the problem can be eliminated.

The first thing to see, is if he can switch from using the channel 4
RF modulator, to a direct hard-wired video connection (either
composite video, or S-Video) with hard-wired audio. These "baseband"
signals are much lower in frequency, don't go through the TV's tuner
at all, and are likely to be a lot less subject to interference. They
look better, too. If his TV and satellite receiver are so equipped,
I'd suggest this approach.

If he can't switch to direct video, using a better-quality coax
arrangement between satellite receiver and TV might help - use a
well-shielded 75-ohm cable, and make sure the connectors at both
ends are well crimped. Avoid the use of 75-to-300-ohm baluns if
possible.

Also, install some ferrites on whatever cable goes from the satellite
box to the TV (video, audio, and/or RF), as close to the TV as
possible. Also install ferrites on the TV power cord, as close to the
TV as possible.

When I say "install", I really mean "recommend that he install". It's
probably best if you _not_ do the installation or modifications
yourself - if you do, he may hold you responsible for anything which
ever goes wrong with the equipment in the future.

It'd also help to read through the information that the ARRL has
gathered (http://www.arrl.org/FandES/field/regulations/rfi-legal/),
and discuss this with your neighbor in a supportive and
non-threatening way (he may not like to hear a blunt "Well, it's your
problem and not mine" even if that is legally the case).

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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