[evlatests] Low Band Status

[Paul Harden]

I have been asked to post this to EVLA Test for all those concerned and 
hope that is appropriate.

With all 28 low band receivers (LBR) built and all but two installed, 
now our emphasis is to clean up the problems.  We have conducted a 
"triage" survey of all low band antennas with reported problems with the 
findings below.  First, a thanks to Dan Mertely, John McClendon, and 
Sterling Coffee for a second set of eyes and many climbs to the apex and 
down into the barrel.  We climbed a bunch of antennas past few days. 
And to Ken for his test runs, diagnostic help, and accommodating us on 
the antennas during non-maintenance times.

Updated status of all antennas here:
http://www.aoc.nrao.edu/~pharden/LBR/lbr.htm

PROBLEM ANTENNAS (in antenna number order)

EA03 - Weak receiver power; receiver removed for repair.
New receiver installed 7/10; returned to operational status.
Has swapped P-band polarization; will fix next week.

EA04 - Weak XLP (X linear polarization)/LCP from receiver.  Problem is a 
short in the XLP side of the P-band dipole.  Will require the dipole to 
be removed from subreflector to repair (possible Antenna Mechanic help 
needed).  There's only one spare P-band dipole assembly; performance of 
the spare has not yet been checked.

EA08 - No receiver.  Will get one installed shortly (receiver was 
"stolen" to repair EA20 with the MJP dipoles).

EA11 - No TCALs.  Problem is a bad Interface Board.  I will build a 
couple of spares to replace this one shortly.  Receiver will also be 
upgraded shortly to proper Tcal and 4-band gain values.

EA12 - Swapped/poor polarization.  Ken's reference antenna.  Discovered 
incorrect installation of P-band dipoles; offset from elevation axis 
reference by 120 degrees.  Dipole was removed and rotated to proper 
configuration on 7/9.  Ken reports now fully operational and we even got 
the polarization right!

EA14 - No receiver.  Will be reinstalled when receiver is repaired.

EA19 - PROBLEM ANTENNA.  Three of the four heliax cables to the Apex are 
bad.  One has a short, the other two have very high loss, as if water 
damaged or a dielectric breakdown.  These are 25-year old cable runs. 
Also, some old unused heliax runs from a previous box-dipole experiment 
congesting cable trays.  These old heliax cables need to be removed and 
replaced.  This requires fully tipping the antenna to gain access via a 
man-lift with 2-3 people to pull the cables.  Will require a decision if 
possible to fix on the array, or a quick 2-3 day trip to the master pad 
to repair.  Next to last antenna on west arm (over the hill on the very 
sandy road).
Note: There are hundreds of flesh-eating flying ants nesting in the Apex 
barrel and under the dish structure.  We are slowly recovering!

EA21 - Low band receiver will be installed when it leaves the barn.

EA23 - Bad heliax cable, XLP/LCP from receiver to Vertex Room.  Needs to 
be replaced.  Last antenna on west arm.  Same logistic problems to 
repair as EA19.

EA27 - No correlated power on YLP/RCP side.  Problem is a short in the 
YLP side of the P-band dipole.  Will require the dipole to be removed 
from antenna to repair (possible Antenna Mechanic help needed).

Thus, EA04, 19, 23, and 27 have problems that will require some serious 
repair effort, likely with the help of the Antenna Mechanics.

The other problems of missing receivers, swapped polarizations, etc. 
should be corrected shortly (within about 2 weeks).  Ken also reported 
no fringes from EA01 and 26.  We'll check those next week Maintenance Day.

Goal is to get some receivers repaired and upgraded to proper Tcal 
values so we can get receivers back into EA08 and EA14 next Maintenance 
Day (July 17) and address some other issues.

Paul