Most of the options for the receiver relate to the filters that limit what we listen to. The original kit being designed for Ham radio users was quite strict in what it allowed. For a radio telescope we want to listen to more...
This switch allows us to bypass the standard filter. You can hear the difference between the two settings in your speaker or headphones. Without the filter you can hear much more noise.
Near the "bandpass adjust" pot you will see there is a jumper called "mute". Lets call the op-amp end of the jumper M1 and the audio stage end of the jumper M2. Then lets define a third point at the junction of C14 and R13 (after the first op-amp amplification stage but before the op-amp bandpass filter stage) and call it A.
You want to install the switch so that either the prefilter signal at A, or the postfilter signal at M1 is switched through to the point M2. ie, in one switch position M2 will be switched to M1, in the other position M2 will be switched to A. When in the A->M2 switch position the bandpass filter is bypassed.
Dave Brodrick has up with a different filter design that isn't as strict as the original. <Benefits>