22apr13: check lbw filterbank.
11mar06: check filterbank

22apr13: check lbw filter bank.

    a2749 (Barbara) reported instabilities in polB of lbw during apr13 runs. They were using the 1230-1470 filter with the 1370 hipass filter.
    On 10apr13 we did a cable test on the 1370 hipass cable going into,out of the filter bank. We saw no jumps in the signal. A loose feed through connector was found at the output of the filter bank (it was tightened). A2749 problems continued after this.
    On 22apr13 a test was done to see if the rf switches in the filter bank were making lousy contact.
The test consisted of:

telescope sitting at az=294, dome=10.9444 degrees.
put the 1 second toggle into port 7 of the cal multiplexer.
Use the interim correlator. 4 boards 12.5 MHz bw. take 20 seconds of data

with the winking cal this gave 10 sets of calon,caloff (1 sec each).

for each of the 9 filters:

switch to another filter then back to the filter in use.
take 20 seconds of data
repeat this 10 times.
then move to the next filter.

The idea is that sometimes the switch may not work correctly and we would see a jump in the levels.
For most of the filters, the 1370 hipass filter was left in front of the filter bank. This was to get rid of the radars,.

this was not done for the filters whose entire band sits below 1370 MHz.

For most of the filters the frequency was set to 1405 MHz (except those filters that did not cover this frequency).
Note: the 1280 hipass filter was not included in the set of data.

The data processing was:

For each filter compute:

cal=calOn-calOff
compute the total power for the cal
normalize the 10onoffs * 10 loops to the median value of the cal
If one of the filter switches gave a bad connection, then the cal deflection would show a jump at the start of the 20 secs of data.

The plots show the calDeflections from the test (.ps) (.pdf):

Page 1: total power cal deflection:

Top Frame: polA, bottom frame PolB
The Colors show different filters being tested.
the horizontal axis has the 10*10 measurements of the caldeflection made for each filter.
The 4 sbc of the interim correlator are overplotted (they were all set to the same frequency).
The vertical dashed lines show where the filter was switched away from and then back to the filter being tested.

Page 2: cal off total power

The total power for each cal off was plotted.
The large variation in the cal deflection for the 1100-1800 filter was caused by a source drifting through the beam.
The blue 1550-1820 filter (blue) had lots of rfi in the band (at 1700 MHz).

Summary:

no jumps were seen in the filter bank switches to the 1-2% level.
The test assumes that the switch problem is intermittent. If it remains for each of the 10 cycles of a switch then the 20 seconds of data is not enough time to see anything drift back to the normal value.

processing: x101/130422/chklbw_13.pro, do1.pro

11mar06: check lbw filterbank

A diagnostic was written to test the lband filterbank.

The data taking consists of:

Set the cal to hcorcal and the cal port to the 1 second winking cal (external port 7 with the 1 second toggle plugged in.

For each of the 9 filters banks: select the filter and the then take 20 seconds of data (10 with cal on, 10 with cal off).

Do this for each of the 9 filters. Then loop back and repeat the sequence 9 times.

times.

processing the data:

Tsys - temperature from sky, omt, ground

Tcal - temperature from cal diode

Ttm - time dependent Temperature caused by the filter switches not closing properly or changes caused by sources drifting through the beam. The changes in Tsys between the calOn,calOff will probably be small (spaced by 1 second).

Gfilt - gain of the filter. This could change if the switches did not close properly

Gif - gain for the rest of the IF. This will change as we adjust the attenuators.

CalDeflection=(calOn-calOff) = (Tsys+Tcal+Ttm - (Tsys +Ttm))GfiltGif=Tcal*Gfilt*Gif

CalRatio = CalDeflection/Caloff = Tcal*Gilt*Gif/(Tsys+Ttm)*Gfilt*Gif=Tcal/(Tsys+Ttm)

For each of these we compute the median spectra over the 10 measurements.

The calDeflection

The calRatio will show variations in Tsys caused by Ttm. Ttm can change if the filter relays do not close properly and increase Tsys. It will also change when sources drift through the beam increasing Tsys. When sources drift through, it should occur in both PolA and polB (since most sources are not highly polarized). The calratio will not be sensitive to changes in the gains.

The data

09mar06. 6 complete passes were made through the filters. The plots show:

CalRatio for the 9 filters (.ps) (.pdf): For each filter there is a separate plot for polA and polB. The median calRatio spectra (over the 10 calonoffs) is plotted. There are 6 in each plot since we made 6 complete passes through the 9 filters (each spectra is separated by about 9*22=200 seconds). The y axis has units of Tcal/Tsys. If a filter did not close properly then you would expect the entire 100 MHz band to be affected. There are some jumps in individual 25 MHz bands. These are probably caused by the digitizer for this band being hit hard by rfi.
CalRatio for the 6 filters measured at 1370-1470 MHz (.ps) (.pdf): 6 filters were measured at 1370-1470 MHz. They are over plotted here to show the calratio measured with different filters. There are 6filters*6 passes over plotted in each plot.
Filter 9 (1280 hipass) shows Tsys variation (.ps) (.pdf): The top figure shows the fractional change in Tsys for polA (black) and polB (red) for the 10 cal off measurements that were made the first time the 1280 hipass filter was measured. Pol A varied by about 10%. PolB was stable so this was not a continuum source passing through the beam. The bottom plot shows the cal deflection. This remained relatively stable. This shows that the temperature was changing rather than a gain variation (since the cal deflection would have seen a gain variation). This variation was not seen in the other 5 passes through the 1280 hipass filter. This variation started when the filter was selected and lasted for the 20 seconds of the measurement. It did not show up in the Calratio plots since the median value of the 10 measurements is close to the normal value. Looking at the spectra, the change was across the entire bandpass.
Conclusions:

The filters do not show any variation in Tsys except for the first measurement of the 1280 hipass filter. On 10mar06 this was repeated and no variation in filter 9 was seen.

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lbw check the rf filterbank

22apr13: check lbw filter bank.

Summary:

11mar06: check lbw filterbank

The data taking consists of:

processing the data:

The data