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Joined: Jul 2002
Posts: 717
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I put in a leviton catv amplifier the other day that had a switch on it labeled FM trap. I was just curious as to what exactly an fm trap does. Is it for filtering out the fm radio broadcast signal that is carried along the cable tv coax from the service provider? That would be my guess, but I have no real idea. Anyone?
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Joined: Jul 2002
Posts: 8,441 Likes: 4
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Yes,
It is also used to filter out strong RF currents from nearby FM radio transmitters.
By activating it, it gives you roughly about 30-40dB of attenuation across the 88-108MHz band.
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Joined: Jul 2002
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Joined: Dec 2003
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Actually I have no idea what an FM trap is doing on a CATV amplifier. I don't know of any cable system that provides normal FM reception in the 88-108Mhz frequency range any more. Cable systems "commandeered" this frequency space for revenue producing channels so filtering out this frequency band is going to cause reception problems with the three or four channels that are carried there. And, even if it happens that you are on an old systen that still carries FM radio why would you want to filter it out?
Sounds to me like this is an off-air amplifier that Leviton adapted and is selling as a CATV amplifier. Just another example of why Leviton (as well as other) structured wiring products aren't worth a hill of beans.
-Hal
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Joined: Jul 2002
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Hal,
Do you live near a strong FM radio transmitter?.
This is why these traps are put in there, it is to take out any herringbone interference caused by such strong signals.
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Joined: Dec 2003
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Yes for off-air. Never for CATV. If you had an ingress problem like that you have big problems. And, like I said, the FM band is used for other things on a cable system. Trapping out 88-108Mhz is going to cause problems.
Like I said, if Leviton sells something like this they don't know what they are doing.
-Hal
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Joined: Jul 2002
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Sorry Hal,
I hate to show my ignorance of how things are done with respect to CATV systems.
We obviously do things totally different over here in little old New Zealand.
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Joined: February 2011
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