[Gb-ccb] Ka Band Receiver / CCB Test Update...
Brian Mason
bmason at gb.nrao.edu
Mon Nov 21 14:10:28 EST 2005
hi Rich- yes, Randy & I agree that there's still another problem, which is
the spread between channels. Those channels were pretty precisely tuned to
a constant voltage output against the hot loads in the lab. (except one or
two channels that had not-readily-fixable low or high detector rf inputs)
It's not clear how much day to day variability there is: the origin of
that idea was the mistaking of a (possibly constant) inversion with a
variable offset. Certainly 14000 on blank sky, 10000 on cold load, and 800
counts on hot loads-- obtained on different days-- are roughly consistent
with a simple constant scale flip.
In any case it certainly makes sense to do a thorough round of Tsys +
linearity measurements with hot + cold loads in the lab with the final
configuration, and watch stability of the levels over a few days with a
hot load.
Brian
--------------------------------------------------------------------
Brian Mason | office: +1(304)456-2338
Associate Scientist | fax: +1(304)456-2229
National Radio Astronomy Observatory | mail: PO Box 2
bmason at gb.nrao.edu | Green Bank, WV 24944
http://www.gb.nrao.edu/~bmason/ |
--------------------------------------------------------------------
On Mon, 21 Nov 2005, Richard Lacasse wrote:
>> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
>> <html>
>> <head>
> 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>
>> _______________________________________________
>> <br>
>> gb-ccb mailing list
>> <br>
>> <a class="moz-txt-link-abbreviated"
>> href="mailto:gb-ccb at listmgr.cv.nrao.edu">gb-ccb at listmgr.cv.nrao.edu</a>
>> <br>
>> <a class="moz-txt-link-freetext"
>> 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>
>> </body>
>> </html>
>>
>>
>> _______________________________________________
>> gb-ccb mailing list
>> gb-ccb at listmgr.cv.nrao.edu
>> http://listmgr.cv.nrao.edu/mailman/listinfo/gb-ccb
>>
>
>
More information about the gb-ccb
mailing list