[Gb-ccb] Ka Band Receiver / CCB Test Update...

Mon Nov 21 13:34:37 EST 2005

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Randy, Brian,

The polarity inversion on the cables does seem to explain why we got
readings in the neighborhood of 14000 on the telescope during our initial
tests.  However, I seem to recall that the CCB readings seemed to vary
quite a bit from one day to the next, 14,000s one day, 10,000s another
etc.  Also, there was a fair spread in the values.  I'm having a hard time
believing that this could be caused by polarity inversion in the cables. 
Maybe you've found only one of a few problems, or can you explain the
variations???

Rich

> Brian Mason wrote:<br>
> <blockquote type="cite"
>  cite="midPine.LNX.4.62.0511191724080.25874 at mimas"><br>
> Thanks Randy, Jason.
>   <br>
>   <br>
> My last hot/cold in the lab, with ccb+receiver, was 19oct. At that
> point I believe that we did *not* have the new cables between the
> ccb+receiver-- the new cables were completed and installed only after
> the Ka receiver had gone back up for spectral line commissioning. The
> 19oct levels showed the expected (4500 count vs cold, 12000 count vs
> hot) power levels, and are summarized in a file called
> ccbTsys19oct05.pdf that I think I sent to the mailing list the
> following week.
>   <br>
>   <br>
>  Brian
>   <br>
>   <br>
> --------------------------------------------------------------------
>   <br>
> Brian
> Mason                          
> | office: +1(304)456-2338
>   <br>
> Associate
> Scientist                  
> | fax:    +1(304)456-2229
>   <br>
> National Radio Astronomy Observatory  | mail:   PO Box 2
> <a class="moz-txt-link-abbreviated"
> href="mailto:bmason at gb.nrao.edu">bmason at gb.nrao.edu</a>                   
> |         Green Bank, WV 24944
>   <br>
> <a class="moz-txt-link-freetext"
> href="http://www.gb.nrao.edu/~bmason/">http://www.gb.nrao.edu/~bmason/</a>      
> |
>   <br>
> --------------------------------------------------------------------
>   <br>
>   <br>
> On Sat, 19 Nov 2005, Randy McCullough wrote:
>   <br>
>   <br>
>   <blockquote type="cite">All,
>     <br>
>     <br>
> Jason and I spent some time today sorting out the proximate cause for
> the
>     <br>
> anomalous readings seen last week with the Ka Band Receiver/CCB setup.
>     <br>
>     <br>
> As you'll recall, Brian reported that, when looking at the sky, he
> would expect
>     <br>
> to see total power counts of about 2,000 to 2,500; but, instead, all
> channels
>     <br>
> seem to be setting somewhere around 14,000 to 14,500 counts.
>     <br>
>     <br>
> After going through many gyrations, Jason and I determined that the new
>     <br>
> TWINAX cable sets had actually swapped the polarity of our differential
>     <br>
> signals going into the CCB's input ports...
>     <br>
>     <br>
> Since this would make our readings appear to be "upside down" (i.e.,
>     <br>
> "full scale" would read "zero", while "zero" would read "full scale"),
> this
>     <br>
> could easily explain the anomaly which Brian reported...
>     <br>
>     <br>
> What I DON'T understand though, is how we could have possibly missed
>     <br>
> this while conducting our "final" lab tests...  Brian, is it possible
> that we failed
>     <br>
> to conduct any hot/cold tests after we introduced the new cables?  I
> realize
>     <br>
> that, by then, our focus had moved to sorting out phase switch
> glitches, etc...
>     <br>
>     <br>
> Anyway, come Monday morning, we'll adjust the polarity of the TWINAX
>     <br>
> cables, check (and/or adjust) the calibration of the 16 amplifier
> boards; then
>     <br>
> run through a series of hot/cold tests to verify our changes...
>     <br>
>     <br>
> INSTRUMENT STATUS...
>     <br>
>     <br>
> At this point, the CCB is running in the Receiver Lab (as ccblab) with
> no input
>     <br>
> ports connected; although the receiver control cable is still attached.
>     <br>
> The "demo_client" was disabled at the end of our testing session; so
> the CCB
>     <br>
> should now be available on the network...
>     <br>
>     <br>
> Randy
>     <br>
>     <br>
>     <br>
>     <br>
>     <br>
>     <br>
>     <br>
>   </blockquote>
> _______________________________________________
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> href="mailto:gb-ccb at listmgr.cv.nrao.edu">gb-ccb at listmgr.cv.nrao.edu</a>
>   <br>
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> href="http://listmgr.cv.nrao.edu/mailman/listinfo/gb-ccb">http://listmgr.cv.nrao.edu/mailman/listinfo/gb-ccb</a>
>   <br>
>   <br>
> </blockquote>
> Hi Brian,<br>
> <br>
> If this is truly the case, then NEARLY everything makes sense (i.e.,
> it<br>
> would explain the "upside-down" nature of our readings on the GBT).<br>
> <br>
> However, regardless of this "swapped" condition on the input signals,<br>
> we STILL measured output voltages (while on the GBT) from all 16<br>
> amplifier boards which were extremely widespread (as opposed to<br>
> being reasonably tightly grouped as we would have expected). With<br>
> this one point alone in mind, once the cables are adjusted, we need<br>
> to look carefully at the performance of the system as a whole while<br>
> still in the lab, check and/or adjust the calibration of the 16
> amplifier<br>
> boards, etc., etc., etc....<br>
> <br>
> Thanks,<br>
> <br>
> Randy<br>
> <br>
> <br>
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