This project is based on prior auto tuner work by Ralph, W5GJV. However, instead of a Foster-Seely type phase discriminator like Ralph used, I chose to use a double balanced mixer (DBM) phase detector with the voltage sample shifted approximately 90 degrees. Doing so shifts the DC output (IF port) indicating the phase error so that there are not two zero crossing points within the useful phase error range, but rather one zero crossing within a +/- 90 deg range, with 0VDC corresponding to a 0 deg phase error.
The phase detector is based on one used by M0BMU in his tuning indicator circuit. The control circuitry is similar to W5GJV’s, but with some changes as needed to deal with the single ended phase detector output, required DC amplification, etc.
I created a short (16 min) video demonstrating the automatic tuner on 630 meters:
The executable program by ON7T for the JT slow modes only runs on Windows platforms and crashed when attempting to run it under WINE. Below is a PHP script that will run on Linux to handle the receive side of things. External applications needed:
arecord, sox, jt9 (part of wsjtx)
No sound device was specified when invoking arecord, this assumes one is using PulseAudio and selects the appropriate sound device from the PulseAudio volume control application.
The 7in. TFT display (BuyDisplay ER-TFTM070-5) and VFO encoder (Bourns ENS1D-B28-L00100L, same as used in Elecraft K3) have been fitted to the front panel. The enclosure is a Hammond 1401P (14W x 10D x 5H) with steel top and bottom covers and aluminum front and rear panels. The display opening was made by drilling small holes around the desired perimeter and filing down, with a slightly rounded front-facing edge. The panel was masked off leaving a small “lip” exposed around the opening and sprayed with stain black paint. The final result created a nice bezel-like appearance to contrast the grainy OEM finish of the panel.
The Teensy 3.5 is just sitting on the enclosure bottom plate, but will eventually be fitted to a protoyping board and mounted to a vertical panel that will be parallel to the front panel.