[RFI] TVI on home cinema audio

[John DeGood]

I had an audio RFI problem with my attic HF antenna at 100 W and an Aiwa 
A/V receiver I purchased for my home.  My audio interference was 
deafening and independent of volume setting, which suggested the audio 
output chain in my case.  After much trial and error I was able to 
finally eliminate the interference with 3 "clamp-on" cores located close 
to the A/V receiver on the 2 surround speaker cables and the AC power 
cable.  It required the maximum number of turns physically possible on 
each of the cores to completely silence the RFI.  The cores applied to 
either the surround speaker cables or the power cable attenuated my 
problem, but only together were they able to eliminate it.

RFI can enter on any number of paths, but since according to your 
description your friend's problem is a function of volume setting and 
occurs even with all inputs disconnected, I'd focus his attention first 
on the AC power cable.  If that doesn't work then attack the power cable 
and speaker cables together.

73, John NU3E

Franki @ ON5ZO.be wrote:

>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
>