[evlatests] More on full 8GHz Bandwidth

[Rick Perley]

    Another full BW test was run last night, this time on 3C286, 
allowing me to properly calibrate the data.  The script observed 3C286, 
and a nearby noise field. 

    Results:

    1)  All seven fully-equipped antennas fringed very well on all eight 
IFs. 

    2)  As expected by Ken, the odd subband issues seen yesterday 
disappeared in last night's tests -- these were evidently caused by 
something left over from the prior phased array tests.   But not all 
subbands are at the right levels, however, with subbands 0 and 15 (or 1 
and 16 in AIPS-language) usually far off -- this must be a requantizer 
issue.    A general pattern is easily seen, although not all antennas 
show this equally. 
                For the BD IFs (B1, B2, D1 and D2), it is always subband 
0 which is low, typically by ~5 to 10 dB.
                For the AC IFs (A1,C1,A2 and C2), it is always subband 
15 which is low, typically by 5 to 10 dB.
    This looks like the 'DC offset' problem.

    3) Six of the seven antennas had correct power levels.  But ea25 did 
not.  The A2C2 and B2D2 IFs were low by about 4 dB.  Furthermore, A2 was 
clearly much noisier than all others -- most easily explained if the 
system temperature is much too high.  Bad attenuator setting?  Strange 
FE bandpass?  (This is unlikely, as A1 -- at an adjacent frequency -- 
looked fine. 

    4) I checked the bandpass stability, since Ken observed 3C286 eleven 
times.  As each observation was only 1 minute long, the accuracy is not 
very high.  But it is good enough to see the stability is very good -- 
no discernible changes at a level of 0.1%.  (But note the time span is 
short, the frequencies were not changed, the the SNR not high). 

    5) Sensitivity seems fairly constant across the band, except for 
those subbands noted above.  (The histogram fitting program is slowly 
grinding through all 64 subbands -- I'll circulate a report when it 
finisheds). 

    6)  Delays are very large.  Given below is a table of the 
approximate values (with signs as defined by AIPS).  I've used the 
proper nomenclature, with the assignments to frequencies as given by 
Ken.   The reference antenna is ea05. 

    Antenna-IF            Delay (ns)
------------------------------------------
    13B2                           -53
    13D2                           -53
    17B2                           -91
    17D2                           -88
    19B2                              1
    19D2                              1
    21B2                           -12
    21D2                           -11
    23B2                            12
    23D2                            13
    25B2                        -159
    25D2                        -119
----------------------------------------
    13B1                         119
    13D1                         112
    17B1                           51
    17D1                           52
    19B1                           96
    19D1                           96
    21B1                         175
    21D1                         175
    23B1                         108
    23D1                         109
    25B1                           35
    25D1                           36
---------------------------------------
    13A2                          33
    13C2                          33
    17A2                          82
    17C2                          84
    19A2                          78
    19C2                          79
    21A2                          66
    21C2                          67
    23A2                          89
    23C2                          86
    25A2                          -5
    25C2                         -25
----------------------------------------
    13A1                        -77
    13C1                        -78
    17A1                        -68
    17C1                        -67
    19A1                      -177
    19C1                      -177
    21A1                       -91
    21C1                       -91
    23A1                     -165
    23C1                     -165
    25A1                    -107
    25C1                     -107
---------------------------------------           

    In summary:  All looks quite nice!