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SMATV Headend buzzing/interference/hum
Posted 01 June 2012 - 04:09 PM
The buzzing is occurring at the actual modulator, not just somewhere down the distribution line. It is also audible/visible throughout the distribution, but is happening right at the source. If I connect a test TV to the test port of the modulator I can hear the buzzing.
If I disconnect the audio cable, the buzzing is still there. If I isolate a problem modulator from the distributed signal, I can still get the buzzing when my TV is connected directly to the TV.
Disconnecting the video cable gets rid of the buzzing.
I'm assuming it's some sort of ground loop or a hum but I can't seem to find it or figure out where to insert some sort of filter. I don't know if maybe I'm just picking up some RF interference from a poorly shielded cable or what is going on. I'm just out of ideas. Any help would be greatly appreciated.
The equipment is :
Dish Network 311 receivers x24
Blonder Tongue BAVM-860SAW channelized modulators x24
Two Tripp Lite PS6020 20 outlet power strips (one on each rack for the receivers)
One Tripp Lite surge protector power strip.
Posted 01 June 2012 - 11:44 PM
If you are guessing ground loop, you don't use a filter for that, you use a ground loop isolatorr. These can be bought for about $10 or so each and are put on input and output RF coaxes.
Edited by AntAltMike, 02 June 2012 - 12:10 AM.
Posted 02 June 2012 - 09:56 AM
I will look in to the ground loop isolator. Thank you.
Posted 02 June 2012 - 10:13 AM
Posted 17 June 2012 - 11:10 AM
There could be just "too much" level, which would cause a buzz from over-modulation, or there could be some distortion of the signal that would cause overshoots (sync pulse edges especially) that could be causing overmod.
These would be the typical "sync buzz".
Posted 25 September 2012 - 07:12 PM
Posted 25 September 2012 - 07:20 PM
That should have simultaneously caused graininess, as the signals got weaker and should have been detectable with a signal strength meter.
The weirdest similar problem I had was an outside coax that made BETTER contact when it got cold and overloaded the downstream amplifier. It would happen when the outside temperature got to maybe 20 degrees or colder but unfortunately, this was a 70 foot wire running down the outside of a 7 story building and it was on the southeast side, so the sunlight would start hitting it immediately upon sunrise and it was always back to "normal" by the time I was called out to service it.
The way we diagnosed it was that I actually stayed in the hotel and had them wake me up at 3:00 AM when a guest called in to complain.
Edited by AntAltMike, 15 September 2013 - 02:48 PM.