[evlatests] C band aliasing tests

[Ken Sowinski]

Two experiments were made today to localize where the suspected
aliased signal may be coming from.

1.  Peter wondered if the change to the transition module
FPGAs last week may have had unintended consequences.  We
tested that by restoring the defomratter in 14A with the old 
firmware and found no change in the behavior of the AA
correlation as compared with the unchanged signal path for CC.
The 16A deformatter was not changed at all.

2.  A bandpass filter (1300/100 MHz) was installed at the
input to the 14A DTA module.  The bandpass we are using
is 1216-1266 so the overlap is not perfect, but correlated
signal was observed.  In this case, too the effect was
still seen in the AA correlation but may have been reduced
a little.

If, on furhter examination, result 2. is shown to be correct
then the culprit must be the downconverter.

Summary of observations for those who may want to look at
the data.  Remember to ask fillm to fill flagged data. 
IAT times:
1.  Transition module test
1815  Begin observation with the old (4 bit) FPGA code
1819  Begin observation with the new (8 bit) FPGA code


2.  Filter test
2015  Filter in place, deformatter gain set to 180(!)
2022  Change deformatter gain to 60.
2023  Change deformatter gain to 100.
2027  Stow antennas.

The large deformatter gain setting was required because less 
than the nominal 50 MHz BW was being fed to the T4.