[evlatests] P-band switched power

[Rick Perley]

Emboldened by the success in applying the switched power at high frequencies (with great benefit), I thought I'd have another try in applying it at P-band — where we had some serious gain stability issues on some antennas.  P-band is littered with strong RFI, so I have never seriouisly attempted to try this before.

To my considerable surprise, the AIPS program 'TYSMO' cleaned up all the data very well — even those in spectral windows where these military satellites have ruined the visibility data!  I suspect this success is because these downlinks are quite continuous — it's sporadic RFI which destroys the differencing process.

After applying the switched power, I compared the resulting calibrated visibilities to those which come from not applying the switched power.  The results are a mixed bag:

      For four antennas, applying the switched power made major improvement in the visibility data —mostly notably ea02 which (as alert readers will remember) suffered gain changes of up to a factor of 10 from scan to scan.
      But for four other antennas, the application of the switched power worsened the visibility stability.
      And three other antennas had to be removed because there was no switched power to apply (ea01, 08 and 14).  Additionally, two antennas (ea18 and 20) had extremely noisy switched power —but TYSMO cleaned these up pretty well.

Given that there are virtually no temperature-induced gain changes for these P-band data (I don't know why — the amplifiers are up in the focus cabin, and suffered major temperature changes) — there is no strong need to apply the switched power (given that it worsened as many antennas as it helped), I have elected to proceed with the uncorrected data.

Rick

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