[evlatests] Three bit samplers

[Ken Sowinski]

On Fri, 14 Nov 2008, Jim Jackson wrote:

> The wiring scheme shown on the block diagram is the one Brent came up
> with a couple years ago.  My impression was it was needed because of
> the architecture and wiring of the correlator. If this one also works
> with the current correlator wiring, it's fine with me.
>
> Cheers,
> Jim

This story has a long history, but it only took Barry
one year to notice.  For a long time it was:

D301 to T304-a(0) and (T304-a(1) and T304-c(1))
D302 to T304-b(0) and (T304-b(1) and T304-d(1))
D303 to T304-c(0) and (T304-a(2) and T304-c(2))
D304 to T304-d(0) and (T304-b(2) and T304-d(2))

which would have allowed the flexibility Barry describes.  About
a year ago Brent expressed a desire to swap b(0) and c(0) to make
routing of signals from two station boards to generate all four
polarization products easier.  That is when the first set of
connections below was drawn.  I believe that the rewiring Barry
suggests would do no harm to the correlator other than revising
nomenclature.

The net effect of these changes is finally to recreate the
tension that always existed in the old correlator of ordering
the IFs ABCD in some places and ACBD in others.

Ken



> At 05:31 PM 11/13/2008, Barry Clark wrote:
>> I admit it has taken me a few too many years to realize it, but we
>> have the three bit samplers wired wrong.
>>
>> T304s have outputs labeled 0 for 8bit sampler, 1,2 for three bit samplers.
>>
>> Connection from D30x to T304-x is (cf block diagrm on wall downstairs)
>>
>> D301 to T304-a(0) and (T304-a(1) and T304-c(1))
>> D302 to T304-c(0) and (T304-b(1) and T304-d(1))
>> D303 to T304-b(0) and (T304-a(2) and T304-c(2))
>> D304 to T304-d(0) and (T304-b(2) and T304-d(2))
>>
>> Better connection is
>>
>> D301 to T304-a(0) and (T304-a(1) and T304-c(1))
>> D302 to T304-c(0) and (T304-a(2) and T304-c(2))
>> D303 to T304-b(0) and (T304-b(1) and T304-d(1))
>> D304 to T304-d(0) and (T304-b(2) and T304-d(2))
>>
>> This would permit operating IFs AC in eight bit mode and IFs BD
>> in three bit mode (or vice versa), which does not work with the
>> current wiring.
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