[evlatests] [Fwd: Re: Current status]

[Robert Hayward]

Regarding the C-Band on Antenna 18. Assuming it is an oscillating
post-amp, we would not have to return it to the lab to replace it so
long as the noise diode calibration path is left untouched.

Regarding the X-Band on Antenna 26, we've been reluctant to add
post-amps to these old X-Bands since these are suppose to be transition
receivers and are intended to be common between the VLA & EVLA as well
as the VLBA.

It is somewhat of a puzzle why the earlier X-Bands seem to have adequate
power but this one doesn't. I checked the SOIDA plots which were done
back in August and it does show the RCP side is about 4-6 dB weaker than
the LCP side. As a general rule, several dB of gain differential between
channels in a receiver is not unrealistic. However, this receiver (X#16)
does seem to be somewhat buggered and probably needs to be returned to
the lab for some TLC. We do have the X-Band that we intended to install
on Antenna 17 which we could use. Obviously this would delay the
installation of an X-Band system on 17 for a while.

For future reference, we can, in principle, swap out the 18 dB post-amps
in the X-Band receivers with the 28 dB amps used in the VLA-style Q-Band
receivers. We free up two 8.0-8.8 GHz IF amps whenever we upgrade a
Q-Band with the 40-50 GHz MMIC post-amps. I suspect this modification
will not be a plug & play change since the Q-Band IF amps probably need
better heat sinking. However, this makes the VLA/VLBA X-Band different
from the EVLA receiver, something we'd rather not see. And we were
hoping not to have to expend any effort modifying X-Bands. It certainly
wasn't in our WBS projections.

As for the K-Band on Antenna 26, do we have a dummy F317 for it or were
we expecting to install the 2nd all-singing, all dancing F317 module. If
not, and we don't have a dummy F317 in our arsenal, there should be one
freed up when the 1st real F317 gets installed on Ant 18 (next week maybe?).

-Bob


Jim Jackson wrote:
> We mainly worked on Antennas 18 and 26 today.  I did not hear of problems 
> with 24 until we got back to the AOC so we didn't do anything with 
> it.  Barry - Which L302 did not lock at C-band in 24?  We have one with 
> some updated firmware Pete and Matt just finished and we want to try it.  I 
> was wondering where to install it and this sounds like as good a place as any.
> 
> Antenna 18:  The same as a couple of weeks ago, we found very low power 
> from the C-band receiver RCP output. The front end group believes there is 
> either a broken semi-rigid cable between the dewar and RF box or a post amp 
> is oscillating.  It is working for now - Brent is having a new cable made 
> up and will replace it. If the problem recurs, we'll check for the 
> oscillation with a spectrum analyzer - the receiver may have to be pulled 
> from the antenna for repair if that is what is happening..
> 
> Antenna 26:  The sync problem is fixed - there is confusion on a command in 
> the new version of the L353 - "Sync Enable" needed to be set to "0" to 
> enable sync, not "1". This will be corrected in firmware in the near 
> future. The L305 is now synchronized. Other than that, the antenna is still 
> sick.  There is insufficient power from the X-band receiver to get 
> sufficient levels to the digitizers on RCP.  LCP is 3dB higher and works 
> but is still very marginal. Post amps need to be added to this receiver. 
> L-Band did not work because the T302 seems to have a problem with the +17V 
> power supply - likely a blown fuse on the DAQ1. It was brought back for 
> repair.  K-band is a complete mystery.  The T303 UX Converter, switches and 
> wiring seem to be fine.  The next step was to check out the receiver and 
> test the LO cable but we ran out of time. I also noticed there is no dummy 
> F317 in this antenna to provide 9.6Hz to the new card cage on the K-band 
> receiver - so even if it was working, there would be no switched power.
> 
> Jim
> 
> 
> t 04:25 PM 10/18/2006, Ken Sowinski wrote:
> 
>>On Wed, 18 Oct 2006, Barry Clark wrote:
>>
>>
>>>X band.  18 is a little weak, but maybe because the delays are misset.
>>
>>Delays almost certainly need help if the antenna is on a
>>previiiously unused pad.  If it is off by more thann about 20 ns
>>looking at the phase slope in line mode  is the easiest way.
>>I put an initial guess in SYSPATHF for alll the pads we expect
>>to use and that can be adjusted.
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> 
> 
> 
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