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: http://www.naic.edu/~phil/talks/fast10/talk_2_tsys.html
Дата изменения: Wed Jul 28 21:15:06 2010
Дата индексирования: Sun Sep 12 01:34:43 2010
Кодировка:
Antenna performance: Tsys
Measure Tsys
with a calibration diode.
Diode power injected via a directional
coupler before the first amplifier.
For most receivers diode injected after
polarizer.
For alfa receiver diode is injected
before the polarizer (at the horn).
Turning the diode on and off gives Tsys in
Units of the diode temperature.
Diode needs to be temperature stabilized.
All drifts in electronic gain can be
removed with the cal diode (assuming the diode is stable).
for cooled receivers you should also monitor
dewar temperature.
Jumps in Tsys are often loose cables,
switches going bad, etc..
Install transfer switches in electronics
path so you can switch the path the polA, polB takes. This helps in
debugging where the problem is.
Misc:
We have ground radiation leaking through the
reflector panels giving a polarized component to Tsys (.1 to .5 degK).
Panels are 1 by 2 meters. The long direction has more leakage. (More
info)