Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!wuarchive!zaphod.mps.ohio-state.edu!ub!dsinc!netnews.upenn.edu!eniac.seas.upenn.edu!depolo From: depolo@eniac.seas.upenn.edu (Jeff DePolo) Newsgroups: sci.electronics Subject: Re: RF Interference from Taxi CB's Message-ID: <28843@netnews.upenn.edu> Date: 26 Aug 90 22:33:51 GMT References: <1491@anaxagoras.ils.nwu.edu> Sender: news@netnews.upenn.edu Reply-To: depolo@eniac.seas.upenn.edu (Jeff DePolo) Organization: University of Pennsylvania Lines: 59 In article <1491@anaxagoras.ils.nwu.edu> aieta@ils.nwu.edu (Michael Aieta) writes: > > >The interference I get is strictly from (what I assume to be highly illegal) >boosted CB signals from what sounds to me like Pakistani cab drivers in >the city. It can be VERY VERY loud, much louder than any signal coming out >of my mixer, and it occurs even with the volume from the >mixing pre-amp is all the way down. I have balanced microphones running into >the mixer (along with line-level signals). This sum is in turn fed to both >a tape machine and the power amplifiers through normal 'guitar' cable (1/4" >2 -wire cable). A while back on rec.ham-radio, as well in a number of the ham rags, there was a discussion about cab drivers/dispatchers using the 10/11m CB and ham bands for their communications. It seems that when the popular 10m mobile radios (e.g. Uniden and Clear Channel) came out, the cab companies found that spending $250 on one of these 25 watt sideband/AM rigs was easier than paying Motorola or GE thousands of dollars and getting real radios. >How would I go about putting an RF filter (I have some basic schematics from >the FCC for TV's, stereos etc.) on my power amps? On my mixer? The mixer >is an Alesis 1622 for you musicians, for you techies it is a monolithic >integrated circuit so I don`t believe I can isolate any pre-amp >components per se. You can start by putting bypass caps across all speaker leads. You can experiment with ferrite chokes on some of the other equipment. I've had good luck installing chokes inside equipment such as preamplifiers and amplifiers in RF equipment. The same may work in your situation. On the shielded cables, try some of the popular wrap-around chokes available at Radio Shack and from most other electronics shops. You will probably find only one or two critical paths that the RF is getting in from. Try coiling all of your cables into tight loops as close as possible to where they connect to any equipment. In general, try everything until you can narrow it down. The problem here is that they aren't always transmitting nearby, so it will be hard to tell what is or isn't working. >How exactly do I get these and how do they get broadcast so f%*#ing loud? >How much power are these guys putting out? FCC limits are 4W, but it sounds >to me like these guys are cranking out hundreds. CB transmitters are 4 watts max AM, 12 watts PEP SSB. 4 watts doesn't sound like much, but if it's nearby, just about anything with a diode in it becomes an instant receiver. Complain to your local FCC field office. If you have cab numbers and companies written down, all the better. Give them all the info. Chances are that you won't see any immediate action, but who knows, they may get around to checking it out. Good luck. --- Jeff -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Jeff DePolo N3HBZ Twisted Pair: (215) 386-7199 depolo@eniac.seas.upenn.edu RF: 146.685- 442.70+ 144.455s (Philadelphia) University of Pennsylvania Carrier Pigeon: 420 S. 42nd St. Phila PA 19104