Re: RF Clipper Diode Design


My understanding of the problem is that he is trying to receive weak FM Band II broadcasts signals in the presence of strong local transmissions.

In order to prevent the SDR becoming overloaded whilst still having sufficient RF gain and sensitivity to receiveĀ  the weaker stations, it is necessary to notch out the strongest signals in order to make better use of the available dynamic range of the receiver in question.

With this frequency spacing at this frequency, the desired fractional bandwidth of the notch filter is very small, requiring some form of High Q resonator.

During one of my previous lives as a TV & Radio broadcast transmission engineer, I have used something similar on Band II FM relay stations, where it was often necessary to notch out transmissions from the site in order to be able to receive the wanted signals that were to be rebroadcast.

The filters that we used were often a 1/4 wave loaded line or helical, enclosed within a metal tube about the size of a domestic fire extinguisher, and each one was tuned to a specific transmission frequency, so unfortunately it's not really a practical solution for home use.


Martin - G8JNJ

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