[evlatests] Delays; Archive data truncation.

[Steven T. Myers]

I second this.  The fundamental thing for WIDAR is what was done
in the transform from lag to freqency space plus anything else
done in the backend (like averaging).  There is probably an equivalent for
other correlator architectures.

Note that in the SDM there is a CorrelatorMode table which is the obvious place 
for the correlator info, but it seems insufficient for our needs (and possibly
ALMAs).

On Tue, 16 Feb 2010, Walter Brisken wrote:

>
> I'm not 100% what the context for this email is, but based on my guess, I
> offer some feedback...
>
> It seems that something in this table should differentiate between an
> intrinsically XF correlator (such as WIDAR) and FX (DiFX, FXCORR) and we
> will need to agree what "FFT_SIZE" and "FFT_OVLP" mean in the context of
> an XF correlator.
>
> -Walter
>
> On Tue, 16 Feb 2010, Eric Greisen wrote:
>
>> The CQ table to which Vivek referred has the following format:
>>
>>
>>               The "CQ" table as used in AIPS
>>              ---------------------------------
>>
>> Table name
>>       'CORRELATOR PARAMETER FREQUENCY TABLE'
>>
>> Table header keywords:
>>       'NO_IF'          1 I
>>       'REVISION'       1 I      1 at present
>>
>> col     name          format    units        Comments
>>   1     FRQSEL         1 I
>>   2     SUBARRAY       1 I
>>   3     FFT_SIZE     Nif I                   FFT_size
>>   4     NO_CHAN      Nif I                   No. of channels
>>   5     SPEC_AVG     Nif I                   Spectral averaging factor
>>   6     EDGE_FRQ     Nif D       Hz          Edge frequency
>>   7     CHAN_BW      Nif D       Hz          Channel bandwidth
>>   8     TAPER_FN     Nif C*8                 Taper function
>>   9     OVR_SAMP     Nif I                   Oversampling factor
>>  10     ZERO_PAD     Nif I                   Zero-padding factor
>>  11     FILTER       Nif I                   Filter type
>>  12     TIME_AVG     Nif F      Seconds      Time averaging interval
>>  13     NO_BITS      Nif I                   Quantization (no. of bits)
>>  14     FFT_OVLP     Nif I                   FFT overlap factor
>>
>>
>> I do not think we need all these things.  We do need the channel
>> bandwidth at correlation if we are to correct amplitudes for the
>> non-closing loss due to non-zero delays.  The VLBA correlator gives in
>> the CQ table the channel width after averaging done in the correlator
>> and the SPEC_AVG done in the correlator.
>>
>> Eric Greisen
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>>
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|:| Steven T. Myers                      |:|  Tenured Astronomer       |:|
|:| National Radio Astronomy Observatory |:|  Ph:  (575) 835-7294      |:|
|:| P.O. Box O, Socorro, NM 87801        |:|  FAX: (575) 835-7027      |:|
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