ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals

Topic Options
Rate This Topic
#160477 - 07/06/06 09:35 PM FM Trap?
macmikeman Offline
Member
Registered: 07/16/02
Posts: 717
Loc: Honolulu, Hawaii
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?
Top
Study Guides for VDV / Structured Cabling Installers
#160478 - 07/06/06 09:43 PM Re: FM Trap?
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
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.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin
Top
#160479 - 07/07/06 02:08 AM Re: FM Trap?
macmikeman Offline
Member
Registered: 07/16/02
Posts: 717
Loc: Honolulu, Hawaii
Thanks Trumpy.
Top
#160480 - 07/08/06 12:47 PM Re: FM Trap?
hbiss Offline
Member
Registered: 12/16/03
Posts: 886
Loc: Hawthorne, NY USA
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
_________________________
www.myphonetechs.com
Top
#160481 - 07/09/06 12:55 AM Re: FM Trap?
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
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.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin
Top
#160482 - 07/09/06 09:46 AM Re: FM Trap?
hbiss Offline
Member
Registered: 12/16/03
Posts: 886
Loc: Hawthorne, NY USA
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
_________________________
www.myphonetechs.com
Top
#160483 - 07/22/06 05:11 PM Re: FM Trap?
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
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.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin
Top

Member Spotlight
Member Since: 11/17/00
Posts: 2232
New in the Gallery:
SE cable question
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box


Who's Online
0 registered (), 40 Guests and 8 Spiders online.
Key: Admin, Global Mod, Mod
 
New in the Gallery:
SE cable question
 
Top Posters (30 Days)
Admin 47
HotLine1 43
gfretwell 19
Ruben Rocha 12
Trumpy 9
 
Newest Members
Scotto, Freecrowder, clee512, Jdscott2005, FAIZAN

ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals