There are a few variables you need to be aware of with reception of
PTV RFI. It sounds different depending on whether or not you are
listening with or without a BFO. It also depends on the passband of
the rx. Another factor is the distance between the set and the rx
antenna. More broadly, the frequency, because PTV RFI on the low HF
bands sounds different from what you get on 15 meters.
I've done some investigating on this. PTV RF is a complex broad
modulated signal that has many components and changes with the video
signal. If the set is tuned to a live sports event, there will be a
lot of rapidly modulated RFI because the picture is constantly
changing. In my case, I listened to the recordings of PTV signals and
thought I had some other problem because what I was receiving didn't
sound like the PTV RFI mp3 recordings on-line. Then I went to a few
consumer electronics outlets with a portable SW BC receiver and walked
around the plasma TVs on display. Again, I thought I was not hearing
what I I was hearing at home, but it turned out that the display TVs
were all set up to show these videos of scenic vistas such as mountain
valleys with the camera slowly panning from left to right. Since that
is an almost static video signal, the RFI generated did not have the
pulsing rapidly modulated sound I heard at home. Then a few started
showing something like a football game and I began to hear exactly the
noise I heard on my receivers in the shack.
So you have to be careful. If you don't think you are hearing PTV in
your shacks, get a portable shortwave receiver (they are useful for
other things around the station anyway) and take it to a store like
Best Buy and walk around the TV sets on display and listen up close.
some of the RF coming from the sets doesn't travel as far so in my
tests, a distant set sounds different from one up close.
73
Rob
K5UJ
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