TV/radio interference

[comatoes]

hello,
apologies for a layperson's question here, but i bought a used sanyo TV today. it has an audio output and i chose to run it through my stereo, which is a hodgepodge of equipment (denon amp so old it doesn't respond to my universal sony remote, boston acoustics A60 speakers a la 1987, etc.). the problem i am having is that the wonderful stereo sound of my classic speakers is ruined by what i think is FM interference (seems to be NPR). i have isolated the problem to the TV itself i think, i seem to be able to hear it even on the internal speakers when i turn them on (loud). so, what can i do to eliminate this? would running the cable through the VCR ground whatever is acting as an antennea inside the TV, or am i way off? sorry for the caveman electronics question.

 

[David Bridgen]

It is unlikely to be interference from another f.m. source.
One of the characteristics of f.m. is capture effect. This describes the phenomena where a signal which is only a couple of dB stronger than another will be heard and the weaker signal be attenuated (by about 30dB.) This is the reason why aviation uses a.m. - a station in distress has a better chance of being heard.
If you have more than one station on the same frequency and the unwanted one is the stronger by only a small margin, you will hear that and not the wanted one.
And an f.m. receiver shouldn't respond to amplitude interference. Its limiter takes care of that.

Your problem could be a fault in the t.v. receiver. Or is the audio on its own 'speaker ok?

 

[mstechca]

do this:

Take two long pieces of wire. hook the connector to one end. now twist the wires together as much as possible and hook the connector at the other end. Make sure the wires have a low enough AWG number.

Twisting wires together prevents some interference from happening.

 

[audioguru]

Mstechca,
That's a good(?) idea, short the TV's audio output. That will get rid of the interference!

Nah, it's too much trouble. It is easier to simply unplug the TV's audio output from the amp. :lol:

Years ago, before cable TV, I made an FM trap from a calculated-length shorted piece of 300 ohm twin-lead and attached it to the antenna input of my TV. It worked pretty well. :lol:

 

[mstechca]

I dont exactly mean twist two unshielded wires together to create a short,

the wires need to be shielded with an insulator.

 

[audioguru]

Hi Mstechca,
You have a good point! :lol:
Maybe Comatoes isn't using shielded (screened) RCA audio cables to connect the TV to his stereo. Shielded cables are much better than twisted wires for reducing hum and radio pickup.

 

[comatoes]

the rca cables are shielded. the antenna input is the same as the cable since the television isn't that old. this would make using wires in such a fashion a problem. this is why i am confused about where this is coming from, i am not picking up a signal from the air, i am talking about cable tv run through a denon amp to a pair of boston acoustics A60s. i do think it is a problem in the tv audio output itself, it is just much easier to hear through the stereo. there are wire inputs for speakers on the back of the tv itself, i don't know if this additional information is helpful or not.

 

[audioguru]

I have seen cable splitters that feed FM to your FM tuner and their TV output doesn't have the FM stations in it to cause your interference. At the same time, their FM output doesn't have TV stations in it to cause interference with FM. :lol: