Automatic Carrier Frequency Tuning CW
TUNE HELPER & SNAP MODE
CW TUNE HELPER
This works as a graphical helper to match your CW RX frequency to the frequency of
your QSO partner. It matches your CW offset to your sidetone frequency and graphically
shows you the difference between the two. This is called "CW SPOT" in the Elecraft KX3
and works very similar in the UHSDR software. The range of the graphical display is +-
150Hz and the accuracy of determining the CW carrier frequency is +-2Hz (relatively
independent of spectrum/waterfall magnify mode, however accuracy is a little better in
higher magnify modes): You will probably be able to match your QSO partners´
frequency -5Hz in real time operation.
A small green box is displayed on the left side of the display above the DSP box: tune
into a CW station and adjust your frequency, so that the little vertical yellow indicator is
exactly in the center of the box --> Done!
how to use it
•
enable "carrier snap" in Debug menu: entry "Do not use: cs" [only use, if you are
brave ;-)]
•
enable CW decoder in CW menu
•
adjust CW decoder threshold, so that CW station modulates the red LED
•
change Demod_mode to CW
•
for highest frequency estimation accuracy: set display menu "spectrum FFT
window" to "Hann"
•
adjust frequency of a CW carrier to match your sidetone by graphically matching
yellow mark to center of green box (above the DSP box)
How does the frequency snap mode work?
The automatic tuning process is based on determining the difference between your
tuning frequency and the carrier frequency of the station you are listening to. It is based
on the results of a complex FFT (which is executed on demand when you use the SNAP
button, but we could also use the FFT of the spectrum display, so the data is already
