Introduction:

    The 430 dome receiver has had trouble with polA during 2011 and 2012. There have been:

• Ripples in the bandpass that changed with time. On,off position would then not cancel the bandpass shape.
• Power dropouts of 5db or more. This was correlated with turning the load switch from antenna->load-> antenna. This was thought to be a problem with the Jennings relay that does this switch.

Summary:

• ripple has been seen in polA and not in polB for much of 2011 and 2012.
• On 18oct12 it was found that the jennings relay for polB was not letting much signal through from the sky.
  
• So prior to 18oct12 polB saying polB had no ripple did not necessarily mean the polB was ok.
  
• The typical period of ripple was 2-3 Mhz. A period closer to 1.5 Mhz has also been seen. Later there was some higher freq ripple < 1Mhz.
  
• the rf  system contains a number of components that could cause this problem. Starting at the omt.:
  
• jennings relay (load,antenna).
• After 18oct12 polB jennings relay was removed.
• radar, radio astronomy switch.
• cavity filter before the dewar.
• The polA input connector was damaged long ago. It  has a C clamp holding it.. (a bit suspicious)
• The filter was replaced by a spare filter, but the ripples continued to come and go.
  
• Various pieces of connecting wave guide.
• Over time various pieces of the above were thought to be the problem.
• We may actually be looking at  various things failing over time.
• Some measurements that may tell us something:
  
• radar, radio astronomy switch:
• The ripple did not go away when the radar, radio astronomy switch was bypassed (11aug11).
• Taking data while  switching between radio astronomy and radar mode showed ripple in both positions of the switch.
  
• Jennings relay: load/sky
• The 2.5 Mhz ripple was also present when the receiver (jennings relay) was on load (26mar12).
• there was a 5db drop in power after a load,sky,load switch. This only occurred once. (26mar12).
  
• when terminations were placed at different positions in the chain (30mar12) we saw large oscillations in the signal when the termination was removed.
  
• This eventually went away during the test...
• The ripple is not always present.
• This makes it harder to test.
• Data taken after 18oct12 (when the damaged  polB jennings relay was removed) showed that polB did not have any ripple.
  

---

History and Measurements in reverse order: (top)

• oct-dec12: a2704 total power mapping shows ripples for more than 1/2 the nights.
• 03dec12: polA cavity filter (with damaged input rf cable) replaced with spare cavity filter from ch.
  
• 19nov12: take data while switching between radar,radio astronomy mode. Ripple in both positions.
  
• x111 data oct12,nov12 shows ripple coming and going.
  
• 30mar12 - terminated input to dewar at various spots looking at ripple.
  
• 26mar12 - looked at polA ripple while on load.
• 5db power dropouts when Jennings relay switched.
• polA ripple doings on,offs on load.
  
• 17mar12: polA ripple continues ..
• An example of a2599 bandpass ripple while on sky.
  
• 11aug11:polA ripple remains when radar/radioastronomy switch bypassed.
• examples of a2599  ripples seen on sky using double position  switching.
  
• 27jul-01aug11: proj a2599 dps sees polA bandpass irregularities.
  
• 28jul11 Andrews connectors tightened. Problem continued on 29jul11 in a2599 data.
• 30jun11  polA radio astronomy switch/radar switch was bad.. repaired
• x111data mar11 - jun11 shows ripple
• 21may11 problem reappeared
  
• 10may11 problem went away after Andrews connector tightened
  
• march11  first signs of ripple

19nov12: take data while switching radio -> radar mode switch

    On 19nov12 spectra were taken while the radar, radioastronomy switched was moved from radio astronomy -> radar mode -> radio astronomy.

The plots show the spectra while the switch was moved (.ps) (.pdf):

• Page 1: total power vs time
• Top 460 secs of data
• black is polA, red is polB
• the jump in polA around 120 secs is when carlos was tapping on the polA output cable of the radar,radioastronomy switch.
  
• bottom: blowup when the switch was turned
• 290 secs. moving radio astronomy to radar
• 300 secs, moving radar mode back to radio astronomy.l
• When the switch was between contacts, the power dropped to 60% of Tsys.
  
• When the switch was in radar mode, Tsys increased by 15%. This is because the monoplexor is in the chain when  in radar mode position.
• Page 2: spectra during switch change. These are the spectra from the bottom plot of page 1.
  
• Top: over plot spectra
• Black in in radio astronomy mode ( at beginning and at end
• Red: moving radio astronomy -> radar
• green: in radar mode
• blue: moving radar mode to radio astronomy mode.
• You can see the ripples in both positions of the radar,radio astronomy switch.
• Bottom: over plot spectra with offsets.
• We started in radio astronomy mode at the bottom of the plot.

Summary:

• The ripples appear in polA in both positions of the radar,radio astronomy switch.
• There are two sets of switches: one to switch the input, and a second set to switch the outputs.
• If the switch is bad, it is not the output contacts (unless both are messed up).
• Previously we saw ripples with the switched bypassed so it's probably not the switch.
  
• When the switch is between positions, the ripples go away.
• the Tsys only drops to 60% so there is still appreciable power in tsys
• this power is probably coming from the lna (with the lousy match when the path is open).
• This might be saying that the ripple is no in the lna or downstream from the lna?
• Switching between radio astronomy and radar mode increases Tsys by about 15%.

nov12-dec12:A2704 430 continuum mapping. polA ripples.

    Project a2704 is doing continuum mapping at 430 Mhz using the dome receiver. Their setup is:

• 430 dome receiver. 12.5 Mhz centered at 430 Mhz.
• interim correlator 2048 channels across 12.5 Mhz. 1 second dumps, 9 level sampling
• ra,dec strips ranging from 60 to 300 secs

• Processing:
• the spectra for each strip in a map was averaged.
• the average spectra was normalized to the median spectra value between 422 and 441 Mhz.
• a 1st order linear and 3rd order harmonic was fit to the normalized average spectra, and then subtracted.
• Display:
• dynamic spectra were then made of the average spectra.
  
• The bottom of the image is the first spectra. The top of the image is the last spectra.
• The 1st spectra of each run is labeled on the left of the image.
• PolA image of   strip averages (.gif)
• The large dark,light variation are the ripples
• The polA cavity filter was replaced on 03dec12.
  
• The ripples were seen on 04dec12, but the went away on 05dec12.
  
• PolB image of strip averages (.gif)
• You don't see the ripples in polB.
• It is easier to see the rfi in polB
• there is a comb spaced by 1.5Mhz
  
• at each comb position there are about 6 spikes spaced by 40 Khz.
• It seemed to go away after 07nov12.
• 431.7-431.85. This is a tone that is not resolved in the  12khz (hanning smoothed channels).
• it wanders over this range during an evening.
  

• Top frame polA, bottom frame: polB
• Each day is color coded with the date (yymmdd) on the left)
  
• an offset has been added to each spectra for display
• Tsys is close 1.0.

summary:

• the polA ripples have been present for more than 1/2 of the a2704 observations.
• The polA notched filter (with the bad input rf cable) was replaced with a spare notched fitler (from the ch) on 03dec12.
• On 04dec12 the ripples returned, but they then disappeared on 05dec12.
• So it looks like the ripples are not being caused by the bad input connector on polA filter.
  
• I won't know if the ripples wreck the total power measurement (but my guess is that they will).
• We need to find what was making the 1.5 Mhz comb
• the rfi a 431.7 is a problem since it wonders over frequency (wiping out multiple channels).   

430 x111 data from oct,nov 12  (top)

• the 25 MHz spectra for each 60 sec scan was averaged.
• the median spectral value between 422 and 441 MHz was used to normalize the spectra
• so if Tsys got large, this would hide it
• a robust linear and 3rd order harmonic fit was done over the 25 MHz
• data outside of 422-441 was weighted to 0.
• The fit was then subtracted from the average spectra. This was to remove some of the bandpass.
  

• the spectra are plotted with an offset for display purposes.
• The vertical scale in Tsys
• the top frame is polA, the bottom frame is polB
• The date and time (h: hour AST) for  each measurement is printed in the left column
• each measurement uses a different color.
• The bottom spectra of each frame is the earliest data for the month. it corresponds to the date at the bottom of the left column.
• Page 1: oct12. Top is polA, Bottom is polB
• PolA:
• there were a few days of ripple (04oct12,09oct12,10oct12 at the start of the month.
• The ripple went away, and then returned at the end of the month (28oct,30oct,31oct.. but missing 29oct12).
• The period seems to be 1-2 MHz (at least for the end of the month).
• 1-2am AST was around 3:30 lst. So we aren't looking at the anti-center.
  
• polB
• Note that spectra below 20oct12 (red) about midway in the frame show very little rfi.
• On 20oct12 the polB jennings relay was finally removed so the signal could then get in from the sky.
• Page 2: nov12 (01 thru 22nov12). data was processed before the end of the month.
• PolA:
• The spectra look ok until 07nov12 When the ripple starts up
• the period is still the 1-2 MHz.
• The large ripple on 19nov12 at 12.5 hours should probably be ignored.
• The sun could have been doing this.
• On 21,22 nov the ripple had disappeared.
• we exercised the radar radio astronomy switch many times on 19nov12.
• But we saw ripple in our 19nov12 data after the test.
• PolB:
• no ripple.
• The rfi spikes are getting through (just like polA).
• The jennings relay is not present in the polB line.

summary:

• oct12:
• polA  ripples were present in 6 of 31 spectra
• the period was 1-2 Mhz.
• the jennings relay was removed from polB after 19oct12.
• So polB measurements were now seeing the sky. No ripple was seen.
• Nov12:
•  polA ripples were present in 7 of 16 scans.
  
• The period looks like it might be less than 1 Mhz.
  

30mar12 - terminate input to dewar at various spots. (top)

    On 30mar12 we terminated the input to the dewar at various locations and then took measurements looking for ripple.
The measurements consisited of:

• Dewar input terminated with 50 ohm load.
• The interim correlator took 25 Mhz data centered at 430 Mhz.  At least 400 1 second integrations were taken at each termination.
• 4 different correlator boards were used to check that there were no problems in the if/lo or correlator (none was seen).

• Waveguide to coax transition ->Jennings relay->
• cal coupler -> elbow->straight line->elbow -> radioAstronomySwitch->elbow->straight line->elbow->
• filter cavity->elbow->elbow->cable ->dewar.
  

• morning :
  
• Terminate at input to cal coupler
• ripple in polA
• Terminate at output of cal coupler
• ripple in polA
• Afternoon:
• hagen's timing box was probably running switching the monoplexor on/off (but it was not in the chain). The blanking switched were off.
  
• terminate at input to RadioAstronomy switch.
• ripple in polA. scan 72
  
• termination -> line->elbow -> filter
• ripple in polA. scan 73
  
• filter -> elbow -> termination -> elbow
• No ripple in polA. scan 74
• hagen's box was turned off toward the end of this scan.
• termination -> filter
• no ripple polA. scan 75
• termination -> line-> elbow -> filter.
  
• no ripple polA. scan 76.
• This is the same termination configuration as scan 73 where ripple was seen.
• The only difference is that hagens box had been on for scan 73,.
• termination->line->elbow -> filter
• no ripple polA. scan 77
• turned on transmitter (no klystrons) and hagens box.
• this was no the same as scan 73 where ripple was seen.
• termination->line->elbow->filter
  
• no ripple polA scan 78l
• turned transmitter off.
• tapped on elbow into filter for seconds 40-70 seconds.
  
• System reconnected, Jennings relay installed.
  
• System on load.
• scan 79- ripple present.
• We never turned the load switch antenna, load (it was always on load) so the Jennings relay probably did not send the switch to load after the installation.
• scan 80,81 - no ripple
• we switche load-> antenna->load before the start of each of these scans. No ripple was seen.

• Page 1: on/off-1
  
• each frames shows a on/off-1 for a 200 second avg on, off.
• black is pola, red is polb.
• top:  termination -> raSwitch
  
• ripple present. scan 72
  
• 2nd: termination -> line->elbow -> filter
• ripple present. scan 73
  
• 3rd: filter -> elbow->termination
• no ripple.l scan  74
  
• 4th: termination -> filter
• no ripple. scan 75
  
• 5th: termination -> line->elbow-> filter
• no ripple. scan 76
• bottom: termination->line->elbow->filter, transmitter on.
• no ripple. scan 77
• Page 2: scan 73 termination -> line -> elbow-> filter
• Top. the spectra for average 1-200 seconds is over plotted on the 201-400 second average
• black,blue is polA.You can see that the do not trace one another.
• red,purple: polB. These overlay one another.
• bottom: The total power (25 Mhz) vs time for this scan
• black is polA, red is polB. the vertical scale is +/- 1% tsys (at 300k)
• there are gain variation in polA (.7%) and polB (.2%)
• The scan lasted for 530 seconds.
  

• Top polA, bottom polB
• The image was flattened using the median spectra for the 530 seconds.
• The clean area to the left of 421 Mhz is where the filter has cut off the power.
• You can see where the ripple is changing with time.

Summary:

• Ripple was seen when a termination was placed:
• before the cal coupler, the raswitch, and termination -> line->elbow->filter
• Ripple went away after the termination was moved to in from of the filter.
• When returning the termination to the previous locations where the ripple had been present, it was no longer there.
• So the presence of the ripple is not always repeatable.
• One interesting think we noticed was that:
• When ripple was  present, removing the termination would cause large (> 30db) oscilllations (probably in the dewar).
• When the ripple stopped, removing the termination to move it to another  spot did not cause these large oscillations.
  

26mar12- PolA ripple with 430 on load.  (top)

    On 26mar12 data was taken with the Gregorian dome on load to check out the polA ripple. It had been noticed previously that the Jennings relay for polA (that switches between load and sky) gave non-repeatable results when switched from load to antenna and then back to load.
 The setup was:

• gregorian dome on load
• interim correlator using 1024 channels across 25 MHz, 9 level sampling and 1 second integrations.
• The 25 MHz bands were duplicated in 4 different correlator bands to look for any variation iin the correlator.
  
• data was taken for about 300 seconds
• Then the Jennings relay was switched load to antenna  and then back to load.

• the entire 25 MHz bandwidth was averaged for these plots. The resulting 1 second values where then normalized the the median value in each sbc (excluding the polA dropout).
  

• Page 1: total power Pola (top) polB (bottom)
• the red dashed lines are where the data taking stopped and then the antenna load switch was moved from load -> antenna->back to load.
• the signal from the  dome was repeated in 4 sbc of the interim correlator.
• You can see the dropout around 1100 seconds. It was about a 5db drop in power.
• Looking at the spectra, there was no rfi, so the switch did not remain on the sky.
• The switch could have been between sky and load.
  
• Page 2 : blowup the vertical scale.
• The full y scale is now 1% of Tsys (tsys=about 300 K  on load).
• You can see the signal wandering in time in both polA and polB. this is probably gain variation.
• polb had a jump of about .002 Tsys at 120 seconds.
• Both pola and polb drifted around at the end of scan 2 (around 650 seconds).
• Page 3: blowup up the plot around 650 seconds where polA and polb moved around.

• The 5 300 second scans were used to measure the stability of spectra density vs time.
• For each 300 sec scan:
• break the scan up into 75sec ON, 75 secOff, 75secOn, 75secOff
• Compute on/off-1 for each pair of 75secon,offs and then plot
• Page 1: 75 second average spectrum
• black is polA, red is polB
• The falloff near 422 MHz is the 422 to 442 rf filter.
• Page 2: scan 1 on/off -1
  
• Black polA in the first 150 seconds has large ripple of about 3 MHz.
• The large bump at 421 is the filter fallloff.
• Page3-6 on/off-1 for scans 2-6
• The 70 second scan 4 where polA jumped by 5db was excluded.

Summary:

• Moving the load switch load->ant->load will occasionally cause a power dropout of about 5db in pola.
• there are some jumps of up to .2% Tsys (@300K) that don't look like they are related to moving the switch (they appear hundreds of secs after the switch).
• There are gain variations of about .4% Tsys (@300K) over about 300 secs in both both PolA and PolB.
  
• PolA has larger ripple than polB
• the period  (in frequency) for the ripple  is about 3 MHz (but it is not constant across the entire 25 MHz band).
  
• the amplitude is up to  +/-.4% Tsys (@ 300K) ..about +/- 1K.
• I also looked at some higher time resolution data (.1 sec dumps) and did not see any 1.2 Hz periodicity in the total power. So the cross heads don't look they are causing problems.
  

17mar12 - a2599 has bad ripple in polA  (top)

    a2599 reported bad  ripple in polA.
The plots show a 300 second average spectra using the wapps (.ps) (.pdf)

• Black is pola, red is polB.
• The 1st two frames used a bandwidth of 25 MHz. the last 2 used 12.5 MHz
• The ripple is in all 4 wapps, so the problem is not in the wapps.

x111 data showing polA ripple mar11 to jun11 (top)

• X111 data is taken whenever the schedule allows.
  
• 1 minute integrations of 25 MHz, 1024 channel are taken for the 430 dome band.
  
• mar11 had 14 separate 1 minute integrations for 430 dome spread throughout the month
  
• apr11 had 29 separate 1 minute integrations for 430 dome.
• may11 had 19 separate 1 minute integrations for 430 dome (thru 16may11).
  
• Each 1 minute integration was averaged and then normalized to a mean value of 1 (Tsys).
  

• The  Andrews connectors for polA were tightened 10may11
• Page1: mar11 with offsets and dates.. top  is polA, bottom is polB
  
• polA: 30mar11 (red trace) has the irregularities
• Offsets have been added for display purposes (page1,page2).
  
• Page2: apr11 with offsets and dates. Top polA, bottom polB
• polA: ripples occur more often. 08apr11 is an example.
• Page3: may11 with offsets and dates (thru 31may11).
• strong ripples at start of month.
• Page4: jun11 with offsets and dates. (thru 22jun11).
• Page5: Over plot band passes mar11,apr11 without display offsets.
• The top two frames are mar11 polA, polB. The bottom 2 frames are apr11 polA,polB.
• Page6: Over plot may11
  
• 1st,2nd frames: polA , polB
• black is data before 10may11, red is data after 10may11.
• 3rd,4th frames with offsets for display
  
• black is before 10may11, red is after 10may11.
• For polA starts to have ripples 6 spectra from the top.
• Looking at page 3 this was 21may11.
• Page7: over plot jun11
• 1st,2nd frames: polA , polB  no offsets
  
• black is data before 08jun11, red is data on and after 08jun11.
• 3rd,4th frames: polA, polB with offsets
• black is data before 08jun11, red is data on and after 08jun11
  

• PolA has shown irregularities  in the band pass:
• 30mar11 - 10may11processing x101/120326/chk430.pro.
• 10may11 Andrews connector tightened, ripples went away.
• 21may11 ripples in polA return
• 10jun11-06jun11no ripples
• 08jun11 - ripples started to get stronger. by 18jun11 pretty strong.
  
• the largest deviation is about .5 Tsys.
• hopefully the repair of the radio astronomy,radar switch for polA will fix this
  

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