FM Notch or FM Band Stop Filter

fm-notch-1

An FM notch filter is used to reject strong FM signals in receiver applications. A good FM Notch filter will reject FM signals and have low insertion loss for signals outside the band.

This is a 9th order Filter with excellent rejection in the FM band. The filter works up to 3 GHz with minimal out-of-band insertion loss. This product is ideally suited for Ham radio applications and Software-defined radio receivers where typically there is minimal internal filtering. In the absence of a notch filter, FM signals can saturate the receiver. The specifications of this filter are comparable to ones on the market that cost at least twice as much.

SPECIFICATIONS

Frequency (MHz) Typical Attenuation (dB)
55 1
75 4
80 8
88 60
98 85
108 25
150 0.8
200 0.5
1000 0.3
2000 0.9
3000 1.8

In Japan the FM band extends from 76 to 95 MHz while in North America it spans 88 to 108 MHz.

NOTE: Connectors are SMA-F

Buy it here.

 

 

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2 thoughts on “FM Notch or FM Band Stop Filter

  1. My general neighborhood in PHX has a bunch of high power FM broadcast transmitters that dramatically raise the noise floor of any receiver that’s broadband, especially scanners that don’t have the greatest front-end filtering in the first place. I’d never realized exactly how bad things were until I received the first of one of these filters and did some experiments with it.

    Results of my experiments are available on my blog at jonadams.com/wireless. The reduction in FM BCB interference power presented to my receivers was amazing. What was a crushing -40 dBm for a few stations was reduced tremendously, and a bunch of receiving anomalies vanished. If you ever wondered why you’re NOT HEARING some things, it may be because the receiver is being whacked with high level FM BCB (or TV or AM BCB) interference and just sits there mute.

    I’ve ordered another of these filters for the scanners in the truck, as when I drive by any of the FM BCB sites the scanners (and even my ham radio gear) tends to receive all sorts of unwanted signals. Won’t be able to fix my transceivers (at least not with this low-power filter, I think rated for about 10 w) but it sure does wonders for everything else.

    Cheers and 73 – Jon N7UV

  2. Oh, and a request – I’d like to see a future version of this with the upper shoulder tightened so that the loss at the bottom of the aviation band (118 MHz) is reduced. I believe I’m getting about 8 dB loss there right now, and KSDL and KPHX ops are at the low end of the band, so it does have an adverse impact on monitoring them. However, I know that it’s tough to design a filter with this much FM BCB rejection and only a 10 MHz transition.

    Cheers and 73 – Jon N7UV

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