TranSystems 2.4 GHz Block Down-converter - Thermal Drift
Most AO40 users have a TranSystems block down-converter at the feed of their receive antenna. There are two basic types, but they both have internal quartz crystal oscillators, and they all drift. This particular plot shows frequency drift over a period of one hour and nineteen minutes.
The test setup consisted of an HP 8660C synthesized signal generator feeding the TranSystems block down-converter via a test antenna co-located on my tower. The output of the down-converter was fed to my Kenwood TS-2000, in CW mode. The receiver was initially set to produce a beat tone of 1000 Hz. The audio output was then measured with my HP frequency counter. The normal Doppler shift associated with AO40 communications masks this long term drift, but it's there all the same.