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RF Issues

G

gr8oldies

We've got em. We're in a building where the tower from another AM station is on the property and it wreaks havoc with everything we record, and even broadcast. Anyone tackled a problem like this?
 
Oh yes.. I have. What are you specifically having problems with? Some generalized things to consider are this. First and formost, make sure you have good grounding. That means copper strap from the consoles and racks to several 8 foot ground rods, or better. With that being said, power can be a MAJOR contributing factor. Radio Shaft has several power strips that offer broadband noise filtering like the 61.2433 or 61.2425, or get a tripplite isobar that has noise filtering. Use bypass caps .01uf Radio Shack # 272-131 to bypass across audio leads that are picking up that AM that's bugging you. The trick with any of this stuff is to isolate WHERE it is coming from (power, audio input, audio OUTPUT,telco, etc.) and knock it down. Hopefully your room is copper screened. If it isn't, you MIGHT have to do that at some point if you cannot eliminate the problems with these other methods. If you need telephone filters, I believe Graybar Electric is able to get them for you. They are specific to the freqency of the offending station. The manufacture is Suttle. Here's what they look like http://www.targetd.com/cgi-bin/onramp?pgm=itemdet.bbx&id=1542AM-50&custnum=&password=&sesid= .

Good luck! (ask more questions.. I'll check back!)
 
OKCR pretty much covered it.

Absolutely avoid unbalanced audio runs no matter how short. Check every balanced audio run for proper grounding. Sometimes lifting the ground on one end of a really long run might have an effect on the RF, but the hum might come up considerably. This depends on how good your studio grounding is.

Sometimes even copper screening doesn't get rid of all of it.

Once I had to bolt the antenna ground radial system to the studio AC electrical ground, since there was a potential difference between them ... but you said it was a different AM service so you probably wouldn't be able to access their antenna ground.

Good luck!
 
Thanks for the answers so far. The RF gets into studio monitors, headphones, our Cool Edit program, all of the boards to varying degrees..lets say the amount of production we keep having to re-do is amazing. We often can't even record our morning show for bits due to the RF.
 
You might want to e-mail or phone the Chief Engineer at a place like KXEN, St. Louis, MO (nice people) a 50kw religious station w/the studio a few feet from the transmitter. You might also pose this problem on the engineering forum here, or at the MI radio/tv board.

My 2 cents for you.
 
The best advice I can give you about RF problems is take it a step at a time and don't let it overwhelm you. You must think it though step by step. Fighting the RF interference beast isn't easy, but it CAN BE DONE. You will NEVER be totally imune to it, but I can tell you that you'll be able to beat it down enough to make your facilities useful enough to carry on with what you need to do. Andy had some great advice on how to go about it. Just don't get discouraged and understand it can be fixed, and it can be tricky. Sometimes you think you have it cured and it'll crop back up. With some more work, you can beat it down again. Bypass caps and filtered power stips are your best easy fixes. Unbalanced anything is a source of trouble, but caps can many times stop major problems with unballanced sources if the run is short enough. If you have a phone system and can't get rid of the R.F. you MIGHT have to filter going into AND out of the system. I've seen that happen in several instances. CAT5 or CAT6 cab be a big help on premise wiring for phones, etc. The cancelling twist makes computer cableing almost imune to RF problems even though it's generally not sheilded.

If you really get stuck, give me an email. I'll e-mail you back and try to help out.
 
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