[RFI] TVI Question

[Dale]

This situation does sound like strong RF is getting into the audio amp stage of the TV.  (Yes, the transistors in the audio output amp that drives the speakers are very nice detector diodes.  Since the sound was reported as being "loud" even with the set off, this suggests a lot of RF was present.)  Ask your brother-in-law two questions:

1.  How many external connections does the TV have?  In particular, does it drive external speakers?

2.  Does the voice sound "like Donald Duck" (implying SSB) or is it intelligible (implying AM)?  

The comemnts from Jim, K9YC, are spot-on for external connections.  Of course, if the only connections are power and a 75 ohm RF input cable, then it is likely that the RF is riding in on one or both of those leads and coupling to the audio stage within the set.  Ferrite chokes added to those cables may help.  BTW: Assuming that the TV has a remote (and I have yet to see any current day set that does not), the TV is never fully "Off", as some circuits have to stay alive to allow the remote to function. 

Please keep us posted as to how this resolves.  Thanks.

73, Dale
WA9ENA
Iowa Section Technical Coordinator
 


-----Original Message-----
>From: Thatcher Deane <thatcher.deane at gmail.com>
>Sent: Apr 24, 2013 12:36 AM
>To: rfi <rfi at contesting.com>
>Subject: [RFI] TVI Question
>
>My brother in law reported some audio RFI to his TV, even when turned off.
>
>"We have had a strange phenomenon happening with our TV set the past 
>week and I wonder if you can shed some light on it.  Three times, maybe 
>four, the past week, a loud voice came through for just a few seconds, 
>clearly overriding the audio on the particular program.  .... We just 
>get four or five words and it is difficult to tell what is being said.  
>It comes through very loud, three or four times louder than the audio 
>setting on the TV.  This morning, something very unusual happened.  The 
>TV was not even on and the voice came through, extremely loud. [My wife] 
>came running out from the bedroom to find out what was happening, so it 
>was not my imagination."
>-------
>I've suggested that this might be CB and that modern Ham equipment 
>usually does not have such problems, but that if a ham is involved that 
>he'd probably be able to help fix it, even thought the fault is usually 
>with the TV.
>
>I'm going to dig out my ARRL RFI book, but does this suggest any 
>particular cause or investigation method to anyone?
>
>AH6SZ
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