A2335 lband wide instabilities sep10
Project a2335 reported instabilities in
polB of their lbw measurements back in jul10. The lbw was brought
down and worked on.
On 07oct10 saw
some instabilities in lbw polA and polB.
Their setup was:
The plots below show the problem:
- lbw in linear pol mode
- the 1280 hi pass and 1230 to 1470 bandpass rf filters were used.
- The tiedowns were left tracking during this observation. This may
have increased the 1 Mhz ripple in the spectrum.
- 300 sec on,off position switching (1 240 second on, off was also
- freq around 1360-1380 MHz
5 is 240 recs
- interim correlator, 9 level, 1 second dumps with 4 boards:
- brd 1 band 1 12.5 MHz polA
- brd 2 band 1 12.5 MHz polB
- brd 3 band 2 25 MHz polA,polB
- brd 4 band 3 25 MHz polA,polB
power vs time (band1) and attenuation vs time (.ps) (.pdf):
- Page 1: total power vs time band 1.
- Light blue:
start of position on scan, purple
start of position off scan
- The source name is shown at the start of each on (dark blue)
- top : polA pwr vs time
- 2nd: polB pwr vs time
- 3rd: za vs time
- 4th: az vs time
- All on/offs are 300 secs on,off except the 2nd 113211 which
was only 240 seconds on,off.
- During the on or off the power should be stable (except for
any tsys za dependence which should be smooth)
- 11754 and 11815 (last 3) show power variations during the
on and off. There is a small change in the last 11727 (4th to last)
- the changes occur in pola and in polB.
- There is a large power jump between 11727 and 11754.
- the za change is minimal.
- band 1 polA,B had no attenuation changes between these
scans (see page 2).
- Looking at nvss, there is no large continuum sources in
- Page 2: attenuation vs time.
- top: rf attenuators. Constant at 0 for the run. The upstairs
if attenuator was also constant.
- 2nd: Downstairs if2gain. polA constant except for a 1db step
in the last on,off. PolB constant for the night.
- 3rd,4th: polA,polB cor attenuators for the 3 bands.
- band 1 constant
- band 2: polB constant. polA 1db step last on,off
- band 3: polB constant. pola 1db step 3,2
- So band 1 gain is constant except for polA in the last on,off.
- total power on,off over plotted,
spectra of on/off-1 for bands 1,2,3:
- Page 1. total power vs time.
- i excluded the 240 sec on,off.
- on source is plotted in black, off source in red.
- top: polA on,off, 2nd polB on,off.
- 3rd: polA,B on source, 4th polA,B off source
- band 1 (.ps) (.pdf)
2 (.ps) (.pdf)
3 (.ps) (.pdf)
- The variations start in the last onoff of 11727 (4th from
- The variations are the same in polA and polB
- The variations occur in all 3 bands.
- The change is up to 2% Tsys in 5 minutes
- Page 2: on/off-1 for the 5 sources. For sources with more than
1 onoff, they are over plotted.
- The vertical scale is degK.
- the level changes for multiple onoffs on the same source.
Implies the gain changes between on,off and cals.
- lbw output power is varying by up to 2% in 5 minutes.
- The on/off -1 showed some 1 MHz ripple. This could have come from
tiedown motion (they were not disabled.).
- The variation occurs in all 3 bands. This implies
- It is not a correlator board since it is in all 4 boards.
- It is before the 2nd mixers since it happens in all 3
- It is the same in polA and polB. These are different paths
through the if/lo except:
- the LO for the first mixer is common to polA and polB.
- The program ran in linear polarization mode. If the linear to
circular chassis was not switching this could also affect both pols.
- Some chassis that process polA and polB have common power
- It has not been reported in any other receivers (although i doubt
if anyone has looked close enough recently).