Shortly after AO-73 was launched, I had decent success working several stations, but only after adjusting my uplink frequency up about 8500 Hz from the published value. Unfortunately, I never calibrated SatPC32 the correct way, so I was always entering that value as a XIT offset to my IC-9100. Before this year’s field day, I figured I would correct the calibration, and had no issue doing this for both FO-29 and AO-7. However I was no longer able to hear myself anywhere on the AO-73 downlink, despite adjusting my uplink by +/-12 KHz.
I had pretty much given up on the bird, when I worked Jeff, NX9B, on FO-29 during Field Day. I emailed him, thanking him for the contact and mentioned my troubles. He responded that he too had issues with the published uplink/downlink relationship, and supplied me with his SatPC32 DOPPLER.SQF entries for AO-73.
I tried his values, and adjusted my Sat32PC “Upl. Calibr. (Hz)” setting until I heard myself. This took ANOTHER 5200 Hz at the start of the pass, shifting upward to 6200 Hz by mid-pass.
I was VERY surprised to find that from the satellite’s point of view (Doppler corrected to reflect the frequencies at the satellite), I was at 145.960 (the middle of the published satellite TX pass-band), and the satellite RX was 435.159. That is 9 KHz outside of the published pass-band for the TX, and 19 KHz above the published relationship between RX and TX. Again, these values are about 6 KHz higher than those used by Jeff.
Unfortunately my testing was limited as the bird went out of eclipse about mid-pass and the transponder was turned off.
I confirmed this again on the 2nd pass at approximately 03:08 UTC. At a satellite TX of 145.960.384, the published satellite RX value would have been 435.139.616. Instead I saw that the RX value was 435.159.616 — this was 20 KHz higher than the published value).
(I verified that the TLE that was being used by Sat32PC matched up with those published by Celestrak On July 27, 2015). I also verified that the AO-73 entry in AmsatNames.txt was correct (39444 13066AE AO-73) )
FUNCUBE-1 (AO-73) 1 39444U 13066AE 15208.17816161 .00000549 00000-0 76602-4 0 9990 2 39444 97.7279 269.4651 0059736 6.9191 353.2833 14.80359877 89338