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Sorry to ask what may be a basic question. I have a used Icom 745. It has a "marker unit" option installed. The manuals says how to adjust it and use it, however it does not say what it does for you.

I've searched around the web... You can buy and make marker units, however I can't find anyone who explains what one is.

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Basically it injects a square wave into the receiver, which shows up as a birdie of sorts every 25kHz or 100kHz (depending on which setting you used for the knob). You can use it to tell you that you've hit a band edge, or check your frequency readout's accuracy, or tweak out any offset for whatever band you're on by adjusting the CALIBRATE knob to zero-beat the marker when the frequency display is showing a multiple of 25 or 100 kHz. The idea is that the marker (being crystal controlled) is more accurate / less drifty than the 745's own VFO.

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  • $\begingroup$ It all makes sense now. Thanks! $\endgroup$
    – scm
    Mar 5, 2022 at 0:38

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