Ham Radio Keyer

Growing up, I got my ham radio license at age 13 and worked a lot of CW on 80 meters. That was great, but my main interested was building my own ham radio equipment, getting it to work, and testing it on the air. One project I did early on was a vacuum tube keyer. It used two 12AU7s to generate dots and dashes, and a 6AS7 as a switch to key the transmitter. It seems strange to use a vacuum tube as a switch, but the 6AS7 was a large tube with low "on resistance." A photo of this vacuum tube keyer with my Heathkit receiver in the background can be seen in the links at right.

A bit later in 1973, I built another keyer using early ICs which at the time were RTL and DTL logic. Cool stuff! The time-base used two discrete transistors, and the dot and dash generator each used a Raytheon RM945D DTL flip-flop. I still have the schematic and photos, see links at right.

When I got into FPGAs, naturally one of my first ptojects was a keyer. Since the dot and dash generation is easily described in terms of states, I created a state machine in VHDL code, and had it working in short order. Later I added a sidetone generator, and a way to control the speed using RS232 commands.

I used a Xilinx Spartan 3A Starter Kit board for this keyer, as I have yet to make my own board. The keyer uses only about 4% of the space available in the XC3S700A FPGA on the board. A photo and source code are available using links at the right.

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