[evlatests] EVLA Hardware

[Rob Long]

I found something interesting at the VLA yesterday while trying to sync 
EVLA antennas! (Read on)

I now have the 5 MHz reference input to the L350 connected to the VLA MS 
rack 5 MHz output instead of the Maser output (on the back of the Maser 
itself.)  This means that if the Maser dies and the VLA switches to 
rubidium or crystal, the EVLA will follow suit.  This maintains 
coherence between EVLA and VLA antennas.  It does mean that delays to 
all EVLA antennas will probably be affected by the extra cabling. (Sorry)

The interesting problem was found when I tried to re-sync EVLA after 
changing the 5 MHz reference.  I found a 7.52 ms difference between the 
VLA 9.6 Hz and the EVLA switched power (on all EVLA antennas.)  I was 
told that the array had been run the previous day (during maintenance) 
on one of the other references while work was performed on the Maser. 
This means that the 5 MHz to the IAT clock was changed, thus changing 
the .1PPS EVLA uses for syncing with the VLA.  I checked the GPS and 
then asked the operator to re-sync the IAT clock/master L-8.  This 
corrected the problem (after re-syncing the L305s in all EVLA antennas.)

Rob