[evlatests] [vlbatests] Phased VLA fringes!

[VLBI Observers]

BK178C has been re-correleated. Sniffer plots are in 
/home/vlbiobs/astronomy/mar13/bk178c/MARK5C/jobs/sniffer/PT

Paul Dyer
NRAO Data Analyst
pdyer at nrao.edu




Jon Romney wrote:
> Great news, congratulations to all.
>
> With respect to
>   
>> The 4 subbands have (sometimes) different delays and amplitudes,
>>     
> this is a "well known" effect, still not understood, in the VLBA
> DDC.  You will probably find it in the PT-FD baseline as well.
> So I'd recommend concentrating on other mysteries at this stage.
>
> Best,
> Jon
>  
>
> Vivek Dhawan wrote:
>   
>> Thanks to Walter, and  "real time"  DIFX, (2 hours/GByte transfer), the VLA
>> clock was found at +1704 usec on April 5th.    Backtracking to projects in
>> March,  Paul Dyer has in short order found all the missing fringes.
>>
>> expt       Date        usec.     BW
>>
>> ty028a   Apr 05    1704     1 MHz
>> bb321N  Mar14    1667     128
>> bb321L  Mar13     1667     128
>> bk178c  Mar01     1670     16
>>
>> The offsets may depend more on bandwidth (we have seen this before)
>> than on time elapsed since March 01. No offset is seen in the monitor
>> point  (VLA_GPS to clock) in the master LO.
>>
>> The ~2msec offset is not apparent on the VLA internally, but now we
>> must find out how and why it happens.  It may also be that the regular
>> VLA data is fine, but the VDIF stream has slipped relative to it.
>> I don't know if that is even a legal thought.
>> Tests must be devised, anyone have ideas?
>>
>> I will set up another real-time session soon.
>>
>> Relatively less significant mysteries remain:
>> The 4 subbands have (sometimes) different delays and amplitudes,
>> especially on bk178 (centaurus A) but that I am attributing to the
>> channels being badly phased. Chan 1 is sometimes lower amplitude.
>>
>>
>>
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>>
>>     
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