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This topic comprises 2 pages: 1 2
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Author
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Topic: Transmitters for Drive Ins.
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Bernie Anderson Jr
Master Film Handler
Posts: 435
From: Woodbridge, New Jersey
Registered: Apr 2000
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posted 12-31-2003 02:33 PM
Yes, I've had it by itself with no audio input hooked up to it. with practically everything off in the house that possibly could create an interference. And I still got the hum/buzz. So I'm pretty sure that it is to do with the transmitter. I've tried every ground/antenna combo I can think of. There was a thing I discovered with it that by accident the antenna wire came off the terminal. The radio in the next room lost it's hum by at least half, although still present. When I went down stairs to turn that radio on, the hun was still present. It seems the further you go, the hum stays the same but the signal is weaker.
Now, could this be possible. These transmitters sat for awhile. I got them and me and a friend worked on it and got it transmitting finally. That night, everything seemed fine. There was a slight buzz but nothing that annoying. It sounded like AM broadcast. When I moved it and since then, it got this buzz/hum, what ever you want to call it. Could a cap possibly stopped working over night? To me the buzz sounds like when you have a florescent light shine into a solar cell; a very familiar sound. At least on a projector , I know how to fix it.
Thanks
Bernie
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Tim Reed
Better Projection Pays
![](/ubbmembers/137h.jpg)
Posts: 5246
From: Northampton, PA
Registered: Sep 1999
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posted 01-01-2004 12:31 PM
Roger that, Jeff, John has it pegged.
Also, unlicensed AM is only legal in a "carrier-current" application. I.E., it must use either the household powerlines or a buried "leaky" coaxial cable as an antenna. It cannot radiate a signal, therefore no aerial can be used. All rf reception must be from the induction field only.
I believe the power level is limited to 20 watts output.
FM is, strictly speaking, illegal for use in a drive-in application. That is because FM behaves differently; you can drive away the block and lose an FM signal, but then pick it up again 100 miles down the road. Therefore, unlicensed FM use is restricted - not by output power or ERP - but by field strength. The restriction is fairly small, too, something like 50 uV/m at 300 ft.
Needless to say, I seriously doubt any drive-in is running FM legally, but the FCC seems to be unconcerned about it; especially since deregulation of the Commission (and the resulting staff cuts).
Whichever system you use, however, one of the most important considerations is proper antenna matching! It can make all the difference in the world in transmitter performance and signal reception. quote: KGAY-FM...95.5 FM...Hollywood!
Phil, you never fail to make me ROTFL!
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