[Difx-users] Correlating Overlapping Bands {External}

[Adam Deller]

Thanks Jan for expanding on what I meant by "channel edge alignment or
channel width"!

On Wed, 23 Feb 2022 at 21:10, Jan Florian Wagner via Difx-users <
difx-users at listmgr.nrao.edu> wrote:

> Hi Joe,
>
> for a VEX-derived plot of frequency bands, you can use a DiFX utility
> under trunk /sites/MPIfR/vex/plotVexChannels.py
>
> The band plot could help you to visualize where the bands are, how they
> overlap, and what the correct zoom band definitions could be, that fall
> entirely in a recorded band at all stations.
>
> If the zoom definitions look okay and fall inside recorded bands, then
> another cause for the "Cannot find a parent freq" error can an unsuitable
> spectral resolution. The error is somewhat misleading in that case.
>
> For correlating experiments with ALMA for example, where recorded bands
> are like
>
> chan_def = &W : 87210.453125 MHz : L : 62.5 MHz : &CH01 : &BBC07 : &cp;
> chan_def = &W : 87151.859375 MHz : L : 62.5 MHz : &CH02 : &BBC07 : &cp;
> ...
>
> a correspondingly fine v2d  FFTSpecRes setting is required, as below,
> otherwise ALMA bands are not considered for Zoom correlation, despite the
> zoom band definition nominally falling into a ALMA recorded band
>
> SETUP setupDefault
> {
>   tInt = 0.4
>   FFTSpecRes =  0.0156250
>   specRes = 0.5
> }
>
> regards,
> Jan
>
> On Tue, Feb 22, 2022 at 6:52 PM Joe Skeens via Difx-users <
> difx-users at listmgr.nrao.edu> wrote:
>
>> Hi all,
>>
>> I'm attempting to correlate data coming from two different types of
>> antennas with different (but overlapping) frequency bands, and I'm having
>> some trouble with setting up a zoom section in the v2d file to do this.
>>
>> As it stands, when running vex2difx, I get a warning saying, "Cannot find
>> a parent freq for zoom band X of datastream Y for antenna Z," and the zoom
>> band is dropped, leading to invalid records when the correlation proceeds.
>> I've tried the ANTENNA parameters addZoomFreq and zoom, and both seem to
>> lead to this outcome. I see in the freqId parameter in the SETUP section a
>> blurb about selecting a parent band, but I'm not sure how this is
>> applied--after selecting the freqIds of interest, there's no change in the
>> warning message. (As a note, I have to select the freqIds of both antennas
>> here because I'm unsure of how to apply different setups for different
>> antennas to a single source if that is possible).
>>
>> Am I committing an obvious blunder here or missing something in my setup?
>> I should also note that I'm attempting to correlate complex data with real
>> data, is this something that is supported in the current version of DiFX,
>> or do I need to convert one of my datasets for compatibility? Any
>> advice/expertise would be greatly appreciated!
>>
>> Best,
>> Joe
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-- 
!=============================================================!
Prof. Adam Deller
Centre for Astrophysics & Supercomputing
Swinburne University of Technology
John St, Hawthorn VIC 3122 Australia
phone: +61 3 9214 5307
fax: +61 3 9214 8797
!=============================================================!
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