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: http://www.naic.edu/~phil/usrproj/s2462/s2462.html
Дата изменения: Thu Aug 27 18:48:45 2009
Дата индексирования: Tue Nov 24 06:30:27 2009
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Tests were done with the lro satellite orbiting the
moon during aug09. The dates were:
16,17,20 aug09: Ao transmits, lro receives.
21aug09: Ao transmits,lro receives followed by lro transmits and
ao receives.
Telescope pointing 16,17,20,21 aug09
The plots show the az,za position of the ao
telescope during the tests as well as the difference between the
telescope position and the ephemeris requested position. A datafile is
also included for each day giving the measured ao positions for each
day (utcSec, ra,dec of date).
On 21aug09 lro transmitted and
then ao Received
during the second part of the experiment (the first half had AO
xmitting and lro receiving). The AO receive setup was:
Use sband Narrow (native circular via a turnstile).
place 10db pads before and after the post amp chassis.
Record 500 Khz complex baseband data for both polA and polB using
the 12 bit a/d converters of the RI.
This band was centered at 2380 MHz.
Note: PolA is right hand circular
and polB is left hand circular (ieee convention)
We did not doppler track the lo's during the experiment so the
frequency of the xmit signal of the satellite will drift due to
the doppler change.
The receive cycle was done toward the end of the pass when
the za was close to the limit (19 deg).
After the receive cycle completed (and the satellite was no
longer being tracked, we fired the cal noise diode.
it was 1 second on, 1 second off. This was repeated about 28
times.
The moon was still in the beam during the firing of the noise
cal.
The 1 second averages excluded the transition region of the cal.
The power decreases with cal measurement. This is because the
telescope was sitting at 19.6 degrees za and the moon was drifting out
of the beam.
The vertical axis is 2* a/d^2 .
PolB has a low level 80-> about 6 counts/sigma. The strong
xmitted signal was arriving in polB. It had about 10db more attenuation
than polA. When the xmitted signal went away, the input powers were
equal so polB levels came out lower.. The Cal measurement still looks
like it worked ok... Next time we should adjust the power levels with
the xmit signal off, put in an extra 10 or 20 db, and then take data...
Page 2:
top,middle: cal scale factors for polA, polB. This shows the 28
separate cal on/offs taken. The green line is the median value
for each. This was used to convert a/d^2 to Kelvins.
Bottom: Tsys for the cal off measurements. Black is polA, red
is polB
Tsys was about 200K. It decreased towards the end because the
moon was drifting out of the beam.
Top,Middle is the average spectra for polA, polB smoothed to 120
Hz resolution. The Tsys includes 1/2 the cal value of 6 Kelvins (since
i averaged over the cal on and the cal off).
Bottom: blowup +/- 1Khz about DC.
There is strong 60 hz in polB. This is because the signal level
was low do to the extra 10db attenuation.
Page 1: polA,B and stokesV. The time is ast hours (gmt-4).
This data was taken during the satellite transmit.
Top,middle: polA,poB
Bottom: stokes V
Defined as (polB-polA)/(polB+polA) or ( LC-RC)/(LC +
RC) (according to Kraus radio astronomy pg 123 this is the correct
sign).
So the signal is about 97.5% circular.
Page 2: 4 second oscillation:
The recevied signal showed a 4 second oscillation in time of a
few percent. it is seen in both polA and polB. This does not correspond
any of the resonant
frequencies of AO.