tv tech help

[beaverjim]

i'm having a problem with a hum in my bed/outside tv's. we have a sd direct tv dvr feeding all tv's. front tv is fed via hdmi cable with no audio problems. the bed and patio tv's are being fed by s and rca audio cables to a rf modulator and passed on via rj6 cable to the tv's. any help or thoughts on this would be appreciated jim

[johnandcaren]

I'm not a big tech guy, but some thoughts:

No hum thru the HDMI is probably because it is digital and not picking up RF interferance.

Other hum is probably an RF being picked up, like an antenna, since that is all analog connectivity. You could try different ground points. In audio systems hum is always a ground problem. Is the RF module groundable? Not sure what RJ6 is.

If the hum sounds moderately low in pitch and constant its probably a 60 Hz feed and the tv may need grounding. If its different, then the wire acting as an antenna is more likely.

Hopefully a smarter guy than me will answer.

[Theberrys]

Jim

I put one of these on the input of the modulator Amazon.com: Raptor GL15 Ground Loop Isolator: Automotive and the hum went away. What you probably have is a ground loop and this is made to eliminate that kind of hum.
Worst case you may need one of these as well http://www.amazon.com/Ebtech-Hum-Vol..._bxgy_e_text_b dut try the Audio Transformer first. The AC Isolator is expensive.

Dick

[beaverjim]

thanks! to both of you i will move forward and try these solutions. thanks again for your response jim

[SCVJeff]

If what Dick suggests doesn't work (but it's usually the culprit), you might need an RF isolator between the modulator and TV. That's easily made by attaching 2ea. 75<>300ohm transformers back to back (tying the 300 ohm leads together) and see how that does ya.

[beaverjim]

i picked up the parts yesterday and am heading over to the mh this am. can't wait to try it! thanks again. jim