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Reviews Categories | Filters, RF: bandpass, lowpass, highpass, RFI/EMI, etc.. | Radio Shack FM Trap 75 ohm Help


Reviews Summary for Radio Shack FM Trap 75 ohm
Reviews: 2 Average rating: 3.5/5 MSRP: $8
Description: Great device for removing the strong FM broadcast stations from intermoding Scanners or other recievers. The filter contains three notches that are spread out to remove most of the fm broadcast band. attn is from 30 to 40 db.
Product is in production.
More info: http://www.radioshack.com
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WILL12943 Rating: 2/5 May 3, 2014 10:35 Send this review to a friend
works great now  Time owned: 0 to 3 months
getting about 31 db loss at 97 MHz
and about 27 db los at 107
and 23 db loss at 88.9
works good now.


NOTE I opened it up as well and was able to make 6 turns on existing in coil with a .120 piece of solid antenna

lo-band is back
also vhf...
also took plastic adjusting for while tuned to offending frequencies and found I had to tighten al the coils to maximum.. lengthening the center coil inside the plastic hold down seems to let more signal pass.. tightening with a pair of plastic tuning pliers lowered the traps center frequency to about 98 mhz.. then tightening the new 6 turn on the input gave about 12 db more for a total of 22 db 88 MHz and old 5 turn on the output gave me about 30.7 db loss at 109mhz

at 65 MHz loss is about 1.2 db and at 46.5 its .2

on high band vhf loss at 113 is 1.2 db and at 135 its about .1 loss
 
KF6CM Rating: 5/5 Jul 10, 2007 16:59 Send this review to a friend
Needs to be adjusted.  Time owned: 3 to 6 months
I have purchased over ten of these filters and found that every one of them only attenuating 88 MHz by 6 db. They were all very consistant. By simply adding one turn to the low frequency notch I was able to knock 88 MHz down by 40 db. With two filters in series I was able to get 80 db of attenuation. Now my scanner will scan.
Scrape off the glue that holds the back plate. Then carefully pry off the back plate. locate the small coil that is on the INPUT terminal. It should have 5 turns. clip out only the coil leaving the parallel capacitor attached. Using 24 gage wire make a new coil with 6 turns. use a .125 dia shaft of a drill bit for a form. attach the new coil across the capacitor. I cheated and used a R&H Spectrum analyzer with a tracking generator to verify that it works. Now the entire FM band is gone! (The middle coil and the coil on the OUTPUT terminal needed no adjustment.) I use an outside diskcone antenna at 50 feet on my scanner.
 


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