Calon,offs were done while tracking the sun and
then moving 2 deg in azimuth off the sun. The setup was:
- A jpl horizons ephemeris was used to track on and then off
- 10 second cal on followed by 10 second cal off was
performed on and then off the sun.
- The sequence was; off sun calon/off, on sun calonoff, off
sun calonoff, on sun calonoff.
- The cal diode is probably around 45K (need to measure in
- When on the sun
- The telescope tracked + 8.4 arcmin in el from the
center of the sun.
- The signal was many times stronger at this offset. Later
mano looked that the sun output, and this was close to an
- When off the sun.
- 2 deg (great circle ) offset in azimuth was used to get
off the sun.
- xband receiver using 8050 to 9200 MHz
- Mock spectrometer used to record the data.
- 7 172 MHz bands centered at:
- Each band spaced by 164 MHz
- 2 pols, 4096 channels/pol, 42 KHz channel width
- spectra dumped once a second
- The total power was computed for each 1 second sample of
each 172 Mhz band. no rfi excision was attempted.
- For each frequency band, the total power was normalized to
the average of the calOff data when off the sun.
Plotting the results:
The plots show the results of the calon,offs
- Page 1: calOn,offs all freq bands
- The x axis is the total power samples (1 per second). 10
calon, 10 caloff,, repeated for the 2 sets
- the y axis units are Tsys (caloff, offsun avg).
- 1st,2nd frames: polA
- 1st : on Sun: calOn,off on sun
- On the sun the signal increased by 2.8 Tsys
- the cal off is a bit stronger than the cal on.. so
the system is saturated
- 2nd: Off sun, calonoff
- calOff has be defined to be 1. the cal is .4 to .6
Tsys. We don't (yet) know how the cal value changes
- 3rd,4th frames: PolB
- 3rd: on sun
- the system level (calon,or off) is less than when we
are off the sun. So we've hit a voltage rail in an
- this is probably happening in the 4.2 -
8 GHz part of the band that has so much power.
- The caloff is stronger than the calOn
- 4th: off the sun. we see a cal deflection of
about .3 Tsys.
- Page 2: same plots blownup showing a single freq band:
- 1,2 polA
- 1 - on sun. little difference between calon and caloff
- the level has increased from 1 to 3.75 units. So the
sun was at least 2.75 Tsys units (since we went into
saturation it must be more that this).
- 2 - off sun. cal is about .5 Tsys.
- 3,4 polB
- 3 - on sun.
- cal off is stronger than cal on
- the level went down from the off sun level
- 4 off sun. cal is about .3 Tsys
- Both polA and polB saturated when we were on the sun.
- PolA level went from 1 to 3.8 Tsys. so the sun is at least
2.8 tsys units (more since it was saturated).
- PolB level decreased at all freqbands when we went on the
- A portion of the band outside the 8-9GHz range is
probably causing the saturation.
- When it hits an amplifier voltage rail, portions of the
spectrum outside the region will decrease.
- this is probably the 4.2 to 8 GHz increase in power
we've seen in the frontend.