[evlatests] [widar-wg] phase flippiing is not in the correlator

[Barry Clark]

As for 2.), I think a new phase is strobed into the L302 on
every command received.  1.) is more difficult.

As I understand the setup,
L301 freq = 12928
L302 freq = 13988 + .01n
13988 MHz is 728,541,666.66667 cycles per tick
10 kHz is 520.83333 cycles per tick
So a one tick timing error is .66667 + .83333 = 0.5 turn.
However, 20 kHz is 1041.66667 cycles per tick, and a one
tick timing error would be .66667 + .66667 = .33333, so
these guys should jump too, and if everybody jumps, the
jump should be 60d, not 180d.

We may have a problem with selecting the sync, but it's not
very obvious.

Ken Sowinski wrote:
> We at last have a clear demonstration that the 180 degree
> phase flipping long reported by Rick has its origin in the
> antennas rather than the correlator.
> 
> Last week Rick provided a file in aid of studying the mapping
> problems which provoked a phase change of 180 degrees at every
> scan in half the antennas.  80 second scans were used so that
> we were able to see the problem in a reasonable amount of time.
> The observation was at L band (SSLO was 988.0 MHz) and the LO
> offset fundamental was 10 kHz.  Multiples for each antenna were
> chosen based on the slot occupied by the station board which 
> processed data from that antenna.  As reported in the past 
> antennas form two groups based on the parity of the multiplier,
> one group flips and the other does not.
> 
> ID   Loc  Mult
> --   ---  ----
> ea19 r1s0  1
> ea01 r1s1  2
> ea02 r1s2  3
> ea09 r1s3  4
> ea25 r2s0  5
> ea28 r2s1  6
> ea24 r2s2  7
> ea03 r2s3  8
> ea18 r3s0  9
> ea23 r3s1 10
> ea04 r3s2 11
> ea08 r3s2 12 (but no L band receiver!)
> 
> The file was modififed so that half way through the antennas in
> rack 1 were no longer sent L302 commands to try to distinguish
> between an L302 and a correlator problem.  The results were clear
> and also allow us to determine which antennas are flipping.
> 
> 1.  Baselines between antennas in rack 1 exhibited no phase flips
> after L302 commands were disabled.
> 
> 2.  Baselines between all antennas in rack 1 and others with even 
> parity exhibited phase flips after L302 commands were disabled.  This 
> is the evidence that antennas in even slots (odd multiples) are the 
> ones which flip.
> 
> 3.  Baselines between all antennas in rack 1 and others with odd
> parity all exhibited no phase flips after L302 commands were disabled.
> 
> 
> The correlator is exonerated, but we are left with two mysteries.
> 1.  What is the L302 doing?  2.  Why is it doing anything?  We
> exepect it to do nothing when commanded to the frequency that it
> is already set to.
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