[evlatests] Closure errors and aliasing at C-band.

[Vivek Dhawan]

Further to the test where insertion of an RF filter eliminated the
closure error at C-band, Jim Jackson is preparing to sweep a CW tone
across C-band and see where/if there is a spurious/aliased response
coming in.

I did (below) the calculation that Barry did in his head, and came
up with an offset of 1.77GHz accurate to ~10%, which puts the
spurious sideband around 3.0 (unlikely) or 6.6 GHz.

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At the time, the natural fringe rate on ant 14 = -0.135 Hz,
on 16 = +0.278 Hz, difference is 0.41 Hz at the (correct)
sky frequency 4.8 GHz.

The oscillating error had a period of 6.6 sec, 0.152 Hz,
(error about 10%) so the frequency offset of the spurious
response is

4.8GHz * (0.152/0.41) = 1.78 GHz.

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Vivek.