CABL Forum - Re: HUM Modulation

Hum can be caused by a lot of things in the cable plant low voltage, bad actives, amplifier power supplies, grounding problems with commercial power. here is a trick I used, if I see only 1 humbar rolling up the screen I am possably looking for an amplifier that is bad or a bad amplifier power pack. If I see two lines rolling up the screen 120 cycle hum a bad ground may be the culprit. A bad ground at someones house can sometimes backfeed to the feeder and affect other customers in extreme casses this can be difficult to isolate. If I see a 120 cycle hum the first thing I do is disconnect the ground at the ground block and see if if goes away. Be careful if there is voltage present at the ground you may have lost a nutral in that case reconnect the ground and call power company they will usually check this quickly. I nutral has been lost and you don't reconnect the ground the customer can loose electrical appliances and even have a fire! Learned this the hard way.

> I have experience with troubleshooting several instances of hum in drop passives. (Neutral fault currents due to difference in power ground/cable ground/ and/or cable ground to ground rod. (Fix - splitter with block capacitors or AC block on input to splitter.)
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> What about hum inside the HFC plant? I've never run across it, but was told it can happen from too much current on line splitters/ dcs, taps?. IS THIS something that you find on newer HFC passives? or mainly old plant? Also, I've been told it can come from power supplies, how do you find and fix this in the HFC portion should it become a problem?
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> LETS KEEP THE TECH POSTINGS ROLLING, THESE are helpful to everyone.
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Re: HUM Modulation