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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:
A diagnostic was
written to test the lband filterbank.
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.