Satgen 12    Accurate Measurement of TCA Time of Closest Approach

As discussed in earlier satgen notes, TCA is preferred to AOS or LOS 
(Acquisition or Loss of satellite ) because it is easier to time,
repeatedly, and accurately. If you have a receiver with a digital
frequency readout, you can pick up a satellites signal and then follow it
as it dopplers down in frequency through suitable steps (Eg 100 Hz for HF
sats,1 KHz for 435MHz sats). Measure the exact time you hear the satellite
signal go through zero beat very lowest note, in the SSB, USB or CW
position. Then quickly retune 100Hz or 1KHz lower and keep repeating the 
measurement. A set of results for a 435.974 satellite was :-
Time      Freq      sec/KHz                Time      Freq      sec/KHz
1106:25  435.9784                          1107:15  435.9774   50
1107:56  435.9764   41                     1108:35  435.9754   39
1109:10  435.9744   35                     1109:48  435.9734   38
1110:30  435.9724   42                     1111:13  435.9714   43
1112:03  435.9704   50                     1113:00  435.9694   57
1114:12  435.9684   72                                           
Note that the 3rd column records the seconds taken to doppler the previous
1 KHz down, ie the doppler rate, and doppler rate is fastest (smallest
number of seconds per KHz ) at or near 435.9748 MHz. For all subsequent
orbits this can be treated as the TCA frequency , and the time at which
the signal dopplers through zero beat at 435.9748 MHz can be treated as 
Time of closest approach, and used to chart orbit period.

Shorts  ... MIR,has again been using 166.121 MHz telemetry in response to 
ground commands, after a break. Sometimes the signal has been surging
wildly. As yet there has been no further Russian comment on Mir battery
problem.  UFOs QRMing Oscar 13. The 105 minute orbit period sat is still
appearing every day , but the 101 minute period sats have not reappeared.

Astra Channels different strength. This occurs because of the different
aerial footprints allocated to some channels. Eg SKy, Sky News, Sky
Movies and Maxwell, are stronger in North UK than, Eurosport, Screensport
Astra through a window.  Yes it is possible. You need a window at least 1
metre square or bigger facing roughly south . Two points need care.
Firstly it should be a single thickness pane , double glazing attenuates
the signal enormously. Second you will get bending of the signal which 
will make elevation a degree or so low.If you have a polar mount this
means ignoring what the mount thinks is the equatorial plane and aiming a
little lower.With an Az El mount there is no problem setting elevation low
for best signal. A 90 cm dish to a 1.4 dB NF LNB gets good results in
Scotland. If the landlord objects you can hide the dish behind curtaining,
ordinary curtains attenuate very little at Ku band.

Soviet Molniya Polar relays use 3.2 to 4.2 GHz, one hover point is about
Az 312 El 43 from UK, the other is Az 33 El 40 approx. Orbita 2 TV 3.870
is on the western one . They also carry the Moscow - Washington hot line,
and, were recently used for the Soviet Shuttle Remote Control Links.
73 de GM4IHJ 21 June 89