[evlatests] EVLA Hardware

[Charles Kutz]

A little more clarification;
Both antennas had a strong birdie at 6.7 GHz. Antenna 11 had a second 
spur (sideband) that was 80.5 MHz below it and antenna 21 had a second 
spur that was 260 MHz above it.
  Unlike past harmonics observed from the P-Band;
(1) these were rock solid and did not drift the slightest. We observed 
down to a 3kHz resolution bandwidth and a 100 kHz span.
(2) these appeared to be two tone amplitude modulated.
(3) These signals were -29dBm in amplitude! as observed in the C-Band 
receiver output path.

Since the P-Band power and cal signals pass through the 4-Band receiver, 
I powered down both receivers in each antenna.

Previously antenna 21 had its P-Band swapped out due to the offending 
6.? GHz spur. But when that receiver was brought back to the lab and 
checked out, there were no spurious signals to be seen.


Chuck Kutz



Rob Long wrote:
> I talked with Chuck about this and that is exactly what we saw on both 
> antennas 11 and 21.  We have measured spurs (nice and steady) at 6.7 GHz 
> and 6.9 GHz.  Disconnecting the cal/monitor and control cable from the 
> Utility rack for P-band makes the spurs (and their harmonics) disappear. 
>  We did not power down the P-band receiver, just disconnected the 
> previously mentioned cable.  We left this cable disconnected when we 
> left and C-band on both antennas seems to behaving nicely now on all 
> IFs.  Chuck is planning to try and reproduce the effect we saw in the lab.
> 
> Rob
> 
> Jim Jackson wrote:
>> Remember that the receiver and T302 have a considerably wider 
>> bandwidth than the 1 GHz bandwidth of the samplers.  We have had 
>> P-band receiver birdies before that did not show up in the bandpass 
>> plots at the default LO frequencies. In fact I think that was the case 
>> the very first time we saw this - the birdies were around 6 or 7GHz.
>>
>> Jim
>>
>> At 07:45 AM 10/4/2007, Charles Kutz wrote:
>>> Also and very importantly, we did not see any P-Band "birdies" in the
>>> passbands.
>>>
>>> Chuck
>>>
>>> Rob Long wrote:
>>> > Chuck and I set up ant 11 at C-band and Ken is right, the T304 
>>> levels do
>>> > not look correct!  We will probably have to make a trip to the antenna
>>> > tomorrow to see what's going on.
>>> >
>>> > The Deformatter rack for ant 1 (and all following antennas) has been
>>> > installed in the new correlator room.  It has power (but was unplugged
>>> > after it was checked out), RF signal cables, etc. and will be ready 
>>> for
>>> > use as soon as Linda installs the fiber cable from the optical 
>>> demux to
>>> > the deformatter rack (probably Monday).
>>> >
>>> > Rob
>>> >
>>> > _______________________________________________
>>> > evlatests mailing list
>>> > evlatests at listmgr.cv.nrao.edu
>>> > http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests
>>>
>>> _______________________________________________
>>> evlatests mailing list
>>> evlatests at listmgr.cv.nrao.edu
>>> http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests
>>