What is an Audio Peaking Filter?

Amateur Radio Asked by hotpaw2 on December 26, 2020

What is an Audio Peaking Filter? And how might that be different from an ordinary (narrow) CW bandpass filter, or from tunable audio filters (with fully configurable upper and lower cutoffs)?

Does a peaking filter have anything in common with an audio notch filter?

One Answer

A standard CW filter operates on the IF (RF after at least one stage of downmixing, but before demodulation). Elecraft's APF operates on the demodulated audio.

The reason most filtering is done at IF is because making a nice sharp filter becomes easier the higher the filter's center frequency (within reason). In Elecraft's opinion, a filter with the more gradual roll-off implied by a center frequency of only ~1kHz is beneficial to CW copying, when used in addition to the ordinary IF filter.

Since this is a bandpass filter, it's the exact opposite of a notch filter, but other than that, it's the same :)

Answered by hobbs - KC2G on December 26, 2020

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