The way MacDoppler and SatPC32 handles Doppler shift is by keeping the frequency a constant on both the uplink and downlink AT THE SATELLITE. This is commonly called Full Doppler Tuning.

As the satellite approaches you, the frequency you receive on the downlink is higher than the frequency at the satellite and decreases as the satellite passes the point of closest approach (when the Doppler shift is zero) and continues to decrease as the satellite approaches LOS.

MacDoppler compensates for the Doppler shift in order to keep the frequency at the satellite a constant. This is advantageous as others can join the QSO and everyone will be at the same frequency at the satellite. It will appear to you that there is no Doppler shift -- the best method and easily accomplished by computer control.

If you tune your receiver up or down, MacDoppler will compensate by tuning your transmitter down or up by the same amount, and then compensate for Doppler shift as above.

Hope this helps. Ron W5RKN

Message: 5 Date: Tue, 27 Jan 2015 18:29:42 -0500 From: Jacob Tennant [email protected] To: AMSAT-BB [email protected] Subject: [amsat-bb] Need help understanding inverting transponder operation Message-ID: CAMM2CtW4axkair6JszYPaqXa7TEx=7V=wxF=3h8uVsHLo7iqMQ@mail.gmail.com Content-Type: text/plain; charset=UTF-8

I am very new to satellite operations and I am running MacDoppler on my home Mac Mini computer and trying to get the modes setup as I am having a little trouble with how / where the program should be tuning my Yaesu FT857D.

As I think I understand it for a inverting transponder (FO-29 for example), the downlink frequency range is 435.800 to 435.900 and that would be USB and the frequency would move lower as the pass happens starting at 435.900 and going down to wards 435.800.

The uplink frequency range is 145.900 to 146.000 and that would be LSB and the frequency would move higher as the pass happens starting at 145.900 and going up to wards 146.000.

Is this correct?

Jake WF8S