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Re: [RFI] LCD TV wipes out AM BC band

To: "Ken Winterling" <wa2lbi@frontiernet.net>
Subject: Re: [RFI] LCD TV wipes out AM BC band
From: "Dale Svetanoff" <svetanoff@earthlink.net>
Reply-to: svetanoff@earthlink.net
Date: Tue, 22 Feb 2011 12:15:18 -0600
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>

Thank you for the prompt feedback.  That is very interesting and brings up 3 
questions in my mind:  1) Does my set have a problem that is specific to it or 
which was caught by Toshiba and then fixed in production?  2) I suspect that 
your radio has lower sensitivity than does the Super Radio III.  To verify the 
concept, I'll have to drag out one of my cheapie sets and try the same test.  
I'll report my test results here.  3) Could there be some sort of interaction 
between my set and the computer system?

A question for you:  Do you have anything else connected to the Toshiba?  You 
would have the AC power cord, of course, but other than a coax to the Antenna 
port, anything else?  I have Audio Output (line level) going to an external 
amp, and the SVGA cable from the computer (going into Input 7).  The signal on 
the coax is from my over-the-air antenna.   

Again, thank you for doing the test.

73, Dale

----- Original Message ----- 
From: Ken Winterling 
To: svetanoff@earthlink.net
Cc: K8RI; rfi@contesting.com
Sent: 2/22/2011 11:48:45 
Subject: Re: [RFI] LCD TV wipes out AM BC band


When I saw you have the Toshiba 19AV600U I checked my Toshiba TV in the shack 
and we have the same model. Â I just tried listening to AM on the cheap AM/FM 
radio that is about two feet from the TV. Â I turned off the TV, tuned in a 
weak AM station, then turned on the TV. Â I didn't notice any change in the 
received AM signal. Â Also, there weren't any "sweeping" sounds.


On Tue, Feb 22, 2011 at 12:34, Dale Svetanoff <svetanoff@earthlink.net> wrote:


An excellent question, plus I should have included the Toshiba model info
in my posting.

I can think of at least two systems within the set that could be the
noise-makers: 1) The switching power supply that operates the whole set.
These days, it is not uncommon to have switching freqs as high as 3 (or
more!) MHz. Â I made no analysis of the noise or its pattern, except that it
is broadband in nature and strong across the AM BC band. Â 2) The other
likely candidate could be the drivers for the CFLs that provide the
backlight. Â I did notice an upward "sweep" in frequency (as heard on the
speaker of the radio) each time I switched on the Toshiba set. Â That sweep
lasted for perhaps 2 to 3 seconds, then stopped. Â My thoughts are that
maybe the CFL drivers are "ramping" up the lamps over that period of time,
or they are adjusting to a pre-set drive level to maintain a given
background intensity.

My set is the Toshiba Model 19AV600U, which seems to be a popular model. Â I
suspect that it has been superceded by something "better" by now, but I
have seen these in hospitals, motels/hotels, commercial establishments, and
so forth. Â Remember, any set that is going to cause a problem in the region
of 1 MHz or so will do so when in close proximity to the antenna of a
victim radio. Â Since most AM BC band radios have integral antennas (usually
ferrite bar or rod types - the one in the Super Radio III is a whopping
200mm long [nearly 8 inches]). Â If anyone does note such interference from
a TV set or monitor, please post to the reflector with info about the
offender. Â Thanks.

73, Dale
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