[evlatests] X-Band Sensitivity -- Superb!!!

[Jim Jackson]

Rick,

Thanks for the encouraging message.  We like to hear news like that.

One question:  Would it be possible (or meaningful) to get these same 
efficiency figures from the six antennas with the Teledyne 3-bit 
digitizers?  It might be interesting to see if or how bad the 
problems with the 3-bit digitizers are actually affecting the bottom 
line. Are we even in a stable enough condition to do this with the 
3-bit digitizers yet?

Cheers,
Jim

At 09:23 AM 11/9/2011, you wrote:
>     As part of the upcoming 'path to completion' review, I'm executing
>some tests to determine the EVLA's basic characteristics.
>     Last night, under ideal conditions, I did a 'sensitivity' test:
>Using old-style 'OSRO' mode (two subbands, 128 MHz width, 2 MHz channel
>resolution), tuned to reasonably placed frequencies in each of the eight
>bands.  I observed 3C147 to establish the amplitude scale, then to a
>blank field 2 degrees away to measure the noise.  Referenced pointing
>was applied.  The usual basic calibration was done.
>
>     Here I report only on x-band -- the others will follow as time
>allows today.
>
>     All antennas -- except ea05 -- which were in the array fringed as
>expected.  (antennas 19 and 20 are out).
>
>     From the naturally-weighted noise maps, we measure the SEFD directly
>using the map rms, using all working antennas.
>
>     8300 MHz:  SEFD = 270 Jy
>     11300 MHz:  SEFD = 250 Jy.
>
>     We can get a good measure of the system temperatures and antenna
>efficiencies by using the switched power measures, after correction by
>the calibration from 3C147.  (The 'raw' Tsys values use the measured
>Tcal provided from engineering.  Any errors in these are measured by
>calibration against a source of known flux density, since the observed
>visibilities have been converted to Jy by the provided Tsys values).
>
>     Adjusting the measured Tsys values by the gain factors gives the
>average Tsys:  (these are eyeball averages -- but the spread is
>impressively small, so they should be pretty decent estimates).
>
>     8300 MHz:  Tsys ~ 28 K
>     11300 MHz:  Tsys ~ 26K
>
>     Finally, we can then measure the efficiencies by using the SEFD values:
>
>     effic. = 5.62*Tsys/SEFD  (where 5.62 comes from the antenna's
>collecting area and Boltzmann's constant).
>
>     8300 MHz:  Effic ~ 0.56
>     8700 MHz:  Effic ~ 0.57
>
>     I guesstimate the accuracy of these values as a few percent.  A
>better analysis will follow, in due time (but well before the
>presentations to our august visitors ...)
>
>     Bottom line:  The sensitivity is considerable better than the
>Project Book specifications (SEFD = 340 Jy at 10 GHz).   As the
>efficiencies are exactly what we expect (and they should be!!!), it's
>the outstanding receivers which are allowing us to boast (just a bit!).
>
>     Congratulations to all!
>
>
>_______________________________________________
>evlatests mailing list
>evlatests at listmgr.cv.nrao.edu
>http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests