Marker Generator

This is the Marker Generator from the 1992 ARRL Handbook. A 4MHz crystal divided down to give 100kHz, 50kHz and 25kHz. These go to the switch on the right, which also switches power to the generator.

The pot at the top was connector to an audio amp (which I have since removed (for reasons lost in the mists of time)) with a headphone out and a little speaker.

In the middle is an LM3909 LED flasher which comes on when either the amp or the marker generator is on. And there's a switch that connects the flashy light to a transistor which gates the marker output, so that you can distinguish the marker from other signals or birdies or whatever.

I have since modified things, the LM3909 is now a Dual-Purpose Battery Indicator (by ZL3TKI, from Radio ZS August 1978, from RadCom May 1978). In doing that I lost the signal keying, so I then added a 555 with Ra = 10k, Rb = 1k, C = 220u -- this gives ~1.7 seconds on and ~0.15 seconds off, which I wired (via a diode and the toggle switch) to the 10k pull-up on U2 (7474 PRE and CLR), disabling the signal for a short bit every ~2 seconds (which was the target before I chose round values for the components).