After three failed pass attempts, Bob, WB4SON, was successful in making his first CW contact through AO-73 this evening.  While the Downlink signal levels were high, Bob was unable to hear his own signal in the Downlink.  The mystery was solved, when a much larger than normal Uplink Correction of +8500 Hz was added on top of the DL/UL Doppler corrections.  So while the normal published DL/UL would have been 145.955/435.145, in reality the actual DL/UL was closer to 145.955/435.155.

That Uplink Correction takes into account any frequency inaccuracies in both the earth station as well as the satellite itself (which is subject to wildly fluctuating temperatures in space).

Bob also notes that the Uplink Correction was varying during the pass, from about +8500 Hz to +10500 Hz.  This is an indication that the orbital elements (TLE) have not been refined well enough this early in the satellite’s life, to be an very accurate predictor of its location in orbit — therefore the Doppler corrections, applied automatically, are not as accurate as they could be.