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#1
12-23-2014, 04:45 AM
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Cable Box generating radio noise?
(Not sure if this is in the appropriate board or not.)
I was testing a new radio I found, tuning around on its manual weather band, when I came across a very weird set of tones and warbling somewhere in the vicinity of 162.6xx MHz. I turned stuff on and off to trace the noise to my Scientific Atlanta Explorer 3250HD cable box (Bright House/TWC). The pitch of the sound starts high when the box is plugged in, and changes pitch several times until settling at a lower frequency until the channel is changed. (it's always a steady frequency, not a sweep) Why would my box be radiating radio noise at this frequency, and what's it using it for, if anything? You'd be completely oblivious to it unless a radio near to the unit was tuned to the frequency it's transmitting on. It doesn't bother me at all - I'm just very highly intrigued and fascinated! EDIT: Further testing reveals another noise at a slightly higher frequency - a constant 1,000 Hz (?) tone that changes waveform when buttons are pressed and channels are changed. This sound also changes markedly whenever the LED display on the front of the box changes. Intriguing...
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Sony Trinitron Fan Last edited by YamahaFreak; 12-23-2014 at 04:57 AM. 
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#2
12-23-2014, 07:24 AM
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Is that a DVR box? You must remember there is a lot of processing going on in a digital cable box, in fact most of them run some form of the Linux operating system and have some rather beefy processors in them.
So you are hearing are sounds made by the processor and driver chips as they perform various functions. Cable boxes, routers and Ethernet switches are some of your biggest offenders when it comes to generating RFI.
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#3
12-24-2014, 05:11 AM
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The 3250HD is a digital cable STB, but is not a DVR (live TV only). I just wonder how and why the specific tones and sounds are made. It's fascinating to ponder.
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Sony Trinitron Fan
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#4
12-24-2014, 01:18 PM
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The CPU clock could be acting as an RF carrier and have the tones because it is being modulated by some data....Even regular digital cable boxes have CPUs now.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
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#5
12-24-2014, 10:50 PM
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Electronic M is correct, its nothing new, here is a 1971 DEC PDP-8 playing music over an AM radio.
https://www.youtube.com/watch?v=akvSE5Z474c
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