[evlatests] 3-bit update 8apr11

[Barry Clark]

While the ea12 sampler is back here anyway, how about removing and
amplifier so it doesn't need the 15 dB pad.

Michael Rupen wrote:
> Rick & Keith got a fair bit done today at the site:
> 
> 1- Checked that the input signals to ea12's samplers are OK,
>    suggesting that the problem is with the sampler rather than (e.g.)
>    a T304 module.
> 
>    - They brought the offending sampler back to the AOC for Mike to
>      play with on Monday.
> 
> 2- Switched input cables for the other samplers, so RCP at the
>    antenna is now labeled RCP at the correlator (and in the resulting
>    archive data sets).
> 
> 3- Put in 15 dB attenuators between the T304s and the samplers,
>    so we can simultaneously feed both the T304s and the samplers the
>    right power levels.
> 
> I did a couple quick checks to show that #2 and #3 indeed work as expected,
> confirming that:
> 
>    - RCP is RCP on all 3 antennas
>    - I can pick attenuator settings that make both the T304s and the
>      samplers happy for all 3-bit samplers
>    - We still have fringes, at roughly the right strength, on all
>      expected baselines and correlator products.
> 
> I'm hoping for 3-bit noise tests on Monday.
> 
>          -- Michael
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