[Gb-ccb] ka/rx integration testing status

[Brian Mason]

All- So as most of you know we connected the ccb to the ka band receiver
this afternoon.  Martin & I have collected some test data and had a quick
pass through it; results from the tests are mixed. We have acquired both
dump and regular integration data. The CCB controls the cal diodes and
phase switches in the expected fashion as far as we've been able to
determine; we see the effects of this in the data as well. A plot of the
integration data with cal a, cal b, both cals, and no cal phases is
attached (it's differenced data so cal a appears negative).

We discovered a potentially serious problem in that there are significant
transients associated with the phase switch transition. The transients are
visible in the averaged dump data out to 20 or 25 usec. It's not clear
where these originate but we suspect either the phase switch itself or
associated circuitry. A plot is attached, along with a plot of a test
without the receiver (phase switch signals going through the test detector
circuit). Our target for beamswitching was to spend 25 usec per phase and
only have to blank 1 usec or so;  if we can't reduce the ringing we will
be forced to switch much more slowly. It's unclear at present what the
implications of significantly slower switching would be as far as noise
goes.

It's also not clear how our current setup might affect these results (the
not-optimal cables, as well as the fact that we still need to optimize the
detector circuit tunings) so these results should be taken with a bit of
caution. We should certainly repeat the tests when we're happy with our
test setup.

 -Brian



-- 
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Brian Mason                           | office: +1(304)456-2338
Associate Scientist                   | fax:    +1(304)456-2229
National Radio Astronomy Observatory  | mail:   PO Box 2 
bmason at gb.nrao.edu                    |         Green Bank, WV 24944
http://www.gb.nrao.edu/~bmason/       |
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