[evlatests] Antenna 13, IFs B and D

[Rick Perley]

    In the morning meeting, I reported that antenna 13's B and D IFs 
were 'dead',
similar to antenna 14. 
    In fact, the situation is rather different.  Read on ...

    The statement I gave was based on 'channel 0' data, which integrates 
over the central
part of the bandpass.  In this case, it represents about 8 MHz of 
frequency width. 
When I analyzed the spectral line data, a rather different picture 
emerged --
channel 8 (or 790 kHz BW) showed perfectly good amplitude from the BD IFs of
antenna 13! 
    What is actually happening is that only the central two frequency 
channels of the
12 MHz BW (representing about 1.5 MHz width) give strong amplitude.  Twelve
other channels are down by a factor of 2 to 4.  Channel #1 is almost as 
good as the
central two channels.  Even more bizarre is the phase reponse -- over 
the 12 MHz
BW, there are about two whole turns of phase.   But these are *not* a 
delay, as
the 'turns' are non-uniform. 
    Exactly the same effects are seen at both L and C bands.  Because of 
our pointing
problems, it was not possible to determine if this effect is present at 
X-band. 

    Something really weird is going on with these two IFs from this 
antenna. 

    The bandpasses of the A and C IFs from this antenna look entirely 
normal.  As
reported by Vivek and Barry, there is no problem with the delays.