[evlatests] 3-bit status

[Keith Morris]

Regarding ea22a 8-bit, this new RMS level seems to have appeared 
yesterday.  For at least the week previous, RMS was consistently in the 
9 - 12 range.



Michael Rupen wrote:
> The new 3-bit samplers were installed on three antennas today:
> ea15, ea22, and ea28. There were some problems with the 3-bit sampler
> for ea12 so Mike brought it back to the lab to work on (see his last
> e-mail).
> 
> Some top-level results from a couple hours of Vivek & I:
> 
> * The basics work for most of the samplers (see ea22-DP0 discussion below):
>   - changing input attenuation changes the state counts in the sampler
>   - gain-slope equalizer seems to work
>   - fringes seen on all baselines & polarizations, except ea22-DP0 --
>     see attached figure 3bit_fringes.pdf
>   - state counts are not beautiful but not ridiculous (after manually
>     setting the attenuators) -- see attached figures ea*_3bit_6apr11.gif
> 
> * IF A as seen on Ken's 3-bit signal summary screen corresponds to
>   Data Path 1 (LCP) on the Station Board (and hence in the resulting data
>   files).  IF C is sent to DP0 and will be labeled RCP.  I suspect this
>   is a labeling error in Ken's code but will track that down tomorrow.
> 
> * ea22 has some odd issues:
>   - 3-bit DP0 (RCP as seen in the data)...
>     (1) shows very odd state counts (overpopulates "edge" states)
>     (2) produces no fringes
>   - 3-bit DP1 seems fine
>   - 8-bit IF A has the unique behavior (amongst the 3-bit antennas
>     at least) that the auto-level setting of the attenuators leads to
>     an rms of 15-16 (consistently) rather than the expected rms of 10.
>     All the other 8-bit samplers I checked, including those on ea15 and
>     ea28, were correctly coming out with an rms of 10.
>   - 8-bit IF A also shows an oscillating amplitude and phase across
>     128 MHz (see attached figure ea28_8bit_128MHz.gif).  Maybe a
>     reflection in a cable?
> 
> * One technical detail:
>   - We did remember to turn off the 8-bit sampler, and to issue a "reset"
>     after switching to 3-bit samplers.  This helped some odd state
>     counts for other antennas/IFs, but *not* ea22-DP0.  We'll try this
>     again tomorrow to be sure.
> 
> All in all, we did better than I expected.  Lots more to do, but it's
> looking hopeful for getting at least one useful measurement this week.
> 
>          -- Michael
> 
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-- 
Keith Morris
National Radio Astronomy Observatory
1003 Lopezville Rd.
Socorro, NM 87801
575-835-7060 (phone)
575-835-7027 (fax)