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Old 8-Dec-2014, 11:43 PM   #1
dbseeker
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FM trap and 7-51 antennas

Is there any need for an FM trap preamp on a channel 7-51 specific antenna?
To be more specific, I have a fringe reception issue on real channel 7 with an antennacraft Y71013 coupled with a RCA RVPRAM IR with the trap set on of course. I have an FM station .7 miles away 89.1 with a strength of +4dbm.
Would like to try a lower noise preamp Kiztech and/or CPA 19 both of which I have and both have no FM trap and use a USVJ to couple. At 62, I don't want to get on the roof anymore if there is no reasonable chance for success.
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Old 9-Dec-2014, 12:07 AM   #2
ADTech
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What is unknown is the sensitivity of your antenna to FM signals.

What is known about your pre-amp is that 1) it's internal FM filter isn't particularly effective at that low of FM frequency and 2) that it's plastic case permits substantial signal ingress, in spite of having a metal plate that helps somewhat.

Bottom line is that there really isn't much of a downside in using one or two FM filters at the input the the preamp to kill off FM from entering it via the antenna's reception path. Better yet, swap out to a CPA19 since you have one and use the FM filters. That amp was exceedingly difficult to overload.
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Old 9-Dec-2014, 1:41 AM   #3
dbseeker
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Each FM filter has it's own noise figure. Can you recommend a low noise figure product for the FM filter that would help me in this marginal fringe reception situation ?
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Old 9-Dec-2014, 1:50 AM   #4
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Would the HLSJ be of any efficacy?
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Old 9-Dec-2014, 11:30 AM   #5
ADTech
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Any filter, whether an FM filter or an HLSJ, will have an attendant noise figure (insertion loss) in the spectrum that is of interest in it passing. It's unavoidable, but the best course is to limit it as much as possible.

Either a Pico-Macom or Holland HLSJ or our (Antennas Direct) FM Filter would be suggested to try out, I would not use the Radio Shack filter as it cuts in at a higher frequency and would affect 89.1 very little. If using the HLSJ, terminate the unused port.
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Old 9-Dec-2014, 9:44 PM   #6
dbseeker
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Thanks for your wonderful expertise!!
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