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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Are those sky frequencies “correct”? I guess if all telescopes are the same it probably is OK.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Cheers<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Chris<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">Jayce Dowell <jdowell@unm.edu><br>
<b>Date: </b>Wednesday, 24 March 2021 at 12:11<br>
<b>To: </b>Adam Deller <adeller@astro.swin.edu.au><br>
<b>Cc: </b>Phillips, Chris (CASS, Marsfield) <Chris.Phillips@csiro.au>, difxusers <difx-users@listmgr.nrao.edu><br>
<b>Subject: </b>Re: [Difx-users] complex support<o:p></o:p></span></p>
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Hi Adam & Chris,<br>
<br>
I've moved on to the VLA+LWA data and am running into a new problem. I <br>
have my frequency setups as:<br>
<br>
# FREQ TABLE #######!<br>
FREQ ENTRIES: 2<br>
FREQ (MHZ) 0: 71.09999999441<br>
BW (MHZ) 0: 9.80000000000<br>
SIDEBAND 0: U<br>
NUM CHANNELS 0: 392<br>
CHANS TO AVG 0: 1<br>
OVERSAMPLE FAC. 0: 1<br>
DECIMATION FAC. 0: 1<br>
PHASE CALS 0 OUT: 0<br>
FREQ (MHZ) 1: 71.99999999441<br>
BW (MHZ) 1: 8.00000000000<br>
SIDEBAND 1: U<br>
NUM CHANNELS 1: 320<br>
CHANS TO AVG 1: 1<br>
OVERSAMPLE FAC. 1: 1<br>
DECIMATION FAC. 1: 1<br>
PHASE CALS 1 OUT: 0<br>
<br>
In my data streams table I have the LWA stations recording complex <br>
double sideband with frequency setup 0 and one zoom band of setup 1. <br>
The VLA antennas are set real upper sideband with frequency setup 1 and <br>
no zoom band. I think this is what I want and mpifxcorr doesn't <br>
complain when I run it. However, difx2fits immediately segfaults when I <br>
try to build a FITS-IDI file. Any suggestions?<br>
<br>
Jayce<br>
--<br>
On 3/10/21 4:19 PM, Adam Deller wrote:<br>
> * [EXTERNAL]*<br>
> <br>
> **<br>
> Glad to hear it!<br>
> <br>
> On Thu, 11 Mar 2021 at 09:58, Jayce Dowell <jdowell@unm.edu <br>
> <<a href="mailto:jdowell@unm.edu">mailto:jdowell@unm.edu</a>>> wrote:<br>
> <br>
> Hi Chris,<br>
> <br>
> After some digging I was able to get to the bottom of this and I am now<br>
> getting results that I am happy with. It was a combination of<br>
> switching<br>
> over to trunk and fixing a bad assumption in my VDIF conversion that<br>
> everyone represents four-bit complex integers in the same way.<br>
> <br>
> Jayce<br>
> --<br>
> On 2/4/21 3:08 PM, Phillips, Chris (CASS, Marsfield) wrote:<br>
> > [EXTERNAL]<br>
> ><br>
> > Hi Jayce<br>
> ><br>
> > I'm working the data from the Long Wavelength Array and I am<br>
> trying to see if we can move from our homegrown correlator to DiFX. <br>
> The two modes I need to support are a LWA-only mode with homogeneous<br>
> data and an "eLWA" mode with heterogeneous data that combines the<br>
> LWA stations with the VLA 4-band system. For the LWA-only mode I<br>
> have 4+4-bit complex voltage data from two 19.6 MHz wide spectral<br>
> windows. I am currently converting these data from the LWA format<br>
> into two VDIF files, one per window, for correlation with DiFX. My<br>
> .input file describes the data as:<br>
> >><br>
> >> DATA FORMAT: INTERLACEDVDIF/0:1<br>
> >> QUANTISATION BITS: 4<br>
> >> DATA FRAME SIZE: 7872<br>
> >> DATA SAMPLING: COMPLEX_DSB<br>
> >> DATA SOURCE: FILE<br>
> >><br>
> ><br>
> > I have never personally tested complex_dsb data with interlaced<br>
> vdif. I have no idea if there could be any “interaction” with the<br>
> VDIF interleaving and the specific data type (I would have thought<br>
> not, but you never know).<br>
> ><br>
> > The issue could also be with interpreting the interlaced VDIF,<br>
> not the complex double sideband.<br>
> ><br>
> > Once you have tested using trunk, not the released version, I<br>
> would try and use some of the vdifio utilities to try and convert<br>
> the interlaced VDIF into plain VDIF - either extracting out one<br>
> thread, or merging into multichannel single thread VDIF. You would<br>
> obviously need to update the DIFX .input (and or .v2d) file and<br>
> vexfile to match the new setup.<br>
> ><br>
> > I would also be using the m5access tools to do things like make<br>
> the autocorrelation (both before and after fiddling with the data<br>
> layout). Check DIFX gives the same auto shape as you get with<br>
> m5spec. If you use a modulated noise source, folding the data<br>
> (m5fold) on the period of the noise cal can be very informative<br>
> also. Also look at the headers and check that the # frames/sec etc<br>
> are what you expect (before and after merging threads etc). If you<br>
> decide it is the interlacing is the issue, I suspect you will need<br>
> to discuss with Walter.<br>
> ><br>
> ><br>
> >> I am less sure about DiFX supporting our eLWA mode. For this we<br>
> have the same 4+4-bit complex voltage data from the LWA stations but<br>
> with a bandwidth of 9.8 MHz. We are combining this with 4-bit real<br>
> voltages from the VLA with 8 MHz of bandwidth and a slightly<br>
> different frequency setup. We currently process these data by<br>
> shifting the center frequency of the LWA data to match that of the<br>
> VLA, running two F-engines with different channelization to arrive<br>
> at the same channel width for both data sources, and then cross<br>
> correlate what overlaps. Is this mode something that DiFX supports?<br>
> >><br>
> ><br>
> > Can you represent this data as VDIF? If you you can probably<br>
> handle the different setup using zoom bands. However if this can be<br>
> done will really depend on the EXACT setup. Basically you need to be<br>
> able to channelise the two setups with the same final frequency<br>
> resolution (ie different FFT sizes will be needed, with the ratio of<br>
> the FFT size matching the ratio of the bandwidth difference. But the<br>
> sky frequency of the frequency points out of the FFT need to match<br>
> exactly (ie even if you could achieve the same frequency resolution,<br>
> if the fine channels are offset by 1/3 of a channel you will have<br>
> problems (if that offset is a simple integer ratio, you can just use<br>
> a higher frequency resolution)<br>
> ><br>
> > I hope this makes sense.<br>
> ><br>
> > Cheers<br>
> > Chris<br>
> ><br>
> <br>
> <br>
> <br>
> -- <br>
> !=============================================================!<br>
> A/Prof. Adam Deller<br>
> ARC Future Fellow<br>
> Centre for Astrophysics & Supercomputing<br>
> Swinburne University of Technology<br>
> John St, Hawthorn VIC 3122 Australia<br>
> phone: +61 3 9214 5307<br>
> fax: +61 3 9214 8797<br>
> <br>
> office days (usually): Mon-Thu<br>
> !=============================================================!<o:p></o:p></p>
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