40 meter QRP Transceiver

This semi-homebrew QRP (low power) CW transceiver is based on the ARK-40 transceiver kit, by S&S Engineering. As supplied by the factory, the ARK-40 uses thumbwheel switches to change frequency. I modified the design by adding a microcontroller to allow for more convenient knob-type tuning.

The redesigned control circuitry uses a BASIC STAMP BS-II microcontroller to read an optical shaft encoder. The Stamp outputs a BCD code to the synthesizer in the ARK-40, replacing the BCD code originally supplied by the thumbwheel frequency selector switches.

The transceiver's operating frequency is displayed on an LCD readout. The frequency is displayed in one of two modes. The first is a "bandspread dial" mode, which simulates an analog dial. The simulated dial scrolls across the display as the frequency is tuned. The second display mode is a conventional digital readout, having 100 Hz resolution. Pushing the main tuning knob toggles between the two modes.

The software for the BASIC Stamp is written in P-Basic. The program turned out to be rather difficult to write, because of the challenge of getting the analog dial to display properly. The STAMP is mounted on a custom-fabricated PC Board, which mounts on an L-bracket attached to the optical encoder shaft. A new front panel was fabricated for the transceiver, and the front-mounted speaker was relocated to the cabinet top to allow room on the panel for the tuning knob and display.

QRP transceiver, showing virtual "bandspread dial" on the LCD display. When the main tuning knob is turned, the dial scrolls across the band in 1 kHz increments. Pressing the tuning knob changes the display to digital readout, and the tuning rate slows to 100 Hz resolution (below).

At power-up, the LCD readout displays the above startup message for two seconds, and then reverts to the bandspread dial mode. In the bandspread dial mode, the radio tunes in 1 kHz increments, for rapid tuning around the band.

This is the assembled synthesizer board from the ARK-40 transceiver kit. This board accepts the BCD code from the microcontroller.

The back of the new front panel, showing the LCD display on the left and the circuit board holding the BASIC Stamp microcontroller on the right.

With its built-in CW keyer and 5 watts of power, the basic ARK-40 transceiver is an outstanding 40 meter CW performer. With the new tuning design, it is a true delight to use.

Modules of the transceiver assembled on my workbench for testing purposes.