[evlatests] A most spectacular failure of 'set-and-remember'?

[Keith Morris]

On ea18, I see A and C changing at the same time, at least to within the 
resolution of the monitor data archive.  However, the attenuators change 
from a suspicious 29 - 31 dB to a more reasonable 16dB.  Somehow they 
knew or later determined the correct value.

We don't archive LO frequencies, so it's impossible for me to know how 
the synthesizers are set.  It could also be the L301.  Recall that at 
S-band the L301 signal can contribute to the total power seen at the 
T304.  If the L301 signal were tuned in-band to the output detector, 
this may force a higher attenuator value.

Alternatively, I have seen S-band observations where the Sirius/XM 
signal appears in the AC tuning, and not in the BD tuning.  This can 
cause a difference in power of about 12-15dB, which is about the step 
size seen in your observation.




On 1/14/2014 8:35 AM, Rick Perley wrote:
>     More information:
>
>     Remarkably, the IF 'A' jump times are *not* the same as the IF 'C'
> jump times.  Won't this invalidate the L302 theory?  In any event, if
> the L302 was wrong, there should be no discernible fringes during the
> time it was wrong.  But the fringes are strong and stable.
>     In no cases were the jump times aligned with source changes.  They
> all occurred in the middle of scans.
>     There is no change in the requantizer gains, so the correlator is
> exonerated.
>
> Keith Morris wrote:
>> ea18 and ea19 both show the same behavior in the T304-a: the input
>> power and input attenuator were constant over the jump (at the nominal
>> values) and the output attenuator and power changed, to their nominal
>> values. This (and the AC-dependence) implies that the L302 was wrong,
>> and became correct, since the output detector is post-conversion.
>>
>> I can look into it further tomorrow.
>>
>>
>>
>> On 1/13/2014 5:17 PM, Rick Perley wrote:
>>>      I'm calibrating 20 S-band databases, taken from November 2013
>>> through January 2014.    Five have been completed without any troubles
>>> (other than the usual satellite RFI).  But one is 'special':
>>>
>>>      For this database, the gains of all antennas jumped up, by a factor
>>> of ~ 2 to 10, at times roughly in the middle of the 90-minute run.
>>> But ...
>>>
>>>      1) Only the A and C IFs jumped.
>>>      2) Each antenna jumped gain at a different time.
>>>      3) The new gain was in fact the correct one (judging from the
>>> calibrated gain values and PSum values).  Hence, *the initial power
>>> setup was too low by factors of a few*.  Somehow, this error was
>>> corrected in the middle of the run.
>>>
>>>      This SB was under program 13B-316.  The data were taken on 06 Dec
>>> 2013.
>>>
>>>      The time patterns of the jumps are curious:
>>>
>>>      1) Antennas 18, 19, 20, 22, 23 and 28 all jumped between 12:47 and
>>> 12:51 (IAT).  All jumps were 'clean' -- no more than one intermediate
>>> value is seen.
>>>      2) All other antennas jumped between 13:20 and 13:45.  Some of
>>> these
>>> jumps were not clean -- the system oscillated between the two states, or
>>> (in one case) hopped around three states, before stabilizing.
>>>
>>>      The initial scan for this run was many minutes long -- more than
>>> enough time for the system to find the 'right' level, and keep it.  But
>>> it didn't, and it didn't ...
>>>
>>>      Any ideas?
>>>
>>>
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