Braodcast problem

[Jd925]

Hi I am hopping to get some help.

I am in chage of a high school low power radio station. We use low power transmitters and radiating cable One "system" is located in the schools main building. Thats where the radio station is. The problem we have is there are 10 outer builings we need to get the signal to. two of these buildings should have there own transmiters and radiating cable. ( the radiating cable has been stung already) But I need to find a way to get basicly the audio from the radio station to these two buildings. Each builing has Fiber optic cable and an alcatell network switch. Each building also has a 50 pair telephone cable ( old not twisted or shieled) Now-- I would used a few pairs of that but electrical runs next to all the phone/data conduit and causes horrible interfearance. any recomendations maybey there is a way to make use of the network.

THANKS

JAke

 

[lakehouse]

Jake-

Sounds to me like you have a ground loop caused by different power sources between buildings. The conductors of the audio path are completing a ground circuit between the devices you are connecting, thus the ground hum.

I had the same problem with hum in the music where we had the music source at one office building feeding to the warehouse PA system via standard multi-pair telephone cable (over 1000 feet). The solution was an Audio Isolation Transformer.

We used a Radio Shack # 273-1374 1:1 Audio Isolation Transformer- its cheap at $3.99. The thing is tiny, we mounted it inside a screw terminal surface-type phone jack with cross-connect wires in and out. We mounted the jack enclosure on the phone backboard near the warehouse amplifier. Its worth a try.

If the distance is great or you have weak signal, boost the line level output at the source with a Bogen or McGowan 1-watt audio amplifier, set the level at about 50% and then adjust the input gain on the remote end.

 

[Jd925]

THANKS

I assume its only one audio channel? So i need one for left and one for right audio?

Thanks Jake

 

[lakehouse]

Yes. If you are pushing stereo to the other building you will need to buy two isolation transformers- one for each channel. In fact as I re-read your initial comments, you have 2 buildings to isolate, try one set and if you succede at one building buy the others...

I suspect with two remote buildings you are using one stereo amplifier to push the output signal parallel to both remote bldgs. The ground loop could be caused between one building or all three, best to invest in a set of isolation xfrmrs for both remote bldgs.

 

[daronwilson]

The radio shack isolation transformers are definately handy for quick fixes, but keep in mind they aren't going to be real friendly to the audio you are sending. Their frequency response is going to limit the quality of the audio, and you might want to consider a better quality transformer designed for that if you notice reduced frequency response.

Another cheap alternative is a 70 volt paging speaker transformer, they aren't 1:1 so you would be transforming the level either up or down, sending it down the phone cable and then reversing the setup to get your recovered audio. These transformers generally will handle the wider frequency response better.

Good Luck!

It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com