[RFI] TVI on home cinema audio

[Franki at ON5ZO.be]

Dear RFI subscribers

I am writing this posting on behalf of a friend of mine, who is trying to solve a
nasty RFI problem. He has never had problems before with this setup (HF beam + kW),
until recently, when his neighbour bought a 'home cinema 5.1' setup, and now there is
a problem. The interference only occurs on bands above 20m (so 18MHz and up), only
with a kW (no problem when running the rig barefoot), and only if the beam points
straight to the neighbour's house (all other bearings don't cause trouble).

The problem is only heard in the audio chain (speakers), the video part (TV+DVD) does
not suffer from the TVI. When doing some 'field tests', they isolated the system by
unhooking the TV cable distribution and all amplifier (surround decoder) inputs.
Still there was the noise coming through the speakers. Ferrite cable clamps or rods
did not help. Other solutions, like putting decoupling capacitors accross the
speakers, are hard to use right now, because the owner does not want his equipment
being 'tampered' with, as this will void the manufacturer's warranty. The speaker
cable is soldered inside the speaker's cabinet, amplifier outputs are mono jacks.
It seems that the level of the TVI-noise goes up and down with the volume setting of
the amplifier. Could it be that the root of the problem is the amplifier/surround
decoder?

Anyone has a clue or idea on how to deal with this problem? All input greatly
appreciated.
73 / TNX.

- ON5ZO