<div dir="ltr"><div><div><div><div>Hi Lupin,<br><br></div>OK, I think I partly understand now. But so you've got two datastreams which you've generated from noise sources, is that right? They have independent noise and a common signal which has a small but non-zero delay? And then you're putting both data streams into DiFX and saying they are from the same physical position, so they get the same delay model applied. How are you calculating the single phase number? Is that a simple average over the whole band? The changing amplitudes due to the requantisation plus the phase ripple could easily account for some of the differences. It also seems like your S/N is absurdly high, which is probably exacerbating a lot of the quantisation-related effects. What if you reduce the amplitude of the common noise source to something a bit more realistic, like a maximum of 1% of the independent noise amplitude?<br><br></div>I don't have an explanation for why the phase differs between an LO of 86000 MHz vs 220000 MHz when you're extracting a 128 MHz subband, but I can only point the finger at quantisation + numerical precision effects coupled with the very high degree of correlation that appears to be present in your setup.<br><br></div>Cheers,<br></div>Adam<br><div><div><div><div><br></div></div></div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On 22 May 2017 at 12:12, Lupin Lin <span dir="ltr"><<a href="mailto:lupin@asiaa.sinica.edu.tw" target="_blank">lupin@asiaa.sinica.edu.tw</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div>Dear Adam,</div><div><br></div><div>Thanks for your repsonse to give the indication.</div><div>For the 1st question, I will further check with the expert of HOPS developer.</div><div><br></div><div>For my 2nd question, the Jan’s code is “m5subband” provided in the latest DiFX version to extract the specific frequency range information from a wide/full band data.</div><div>The original input is also the 2-bit VDIF file. </div><div>I just compare with "the cross-correlation with two 2-bit wide band VDIF files at a specific frequency range using the zoom-band mode" and "one data subtracted a the same frequency range to cross-correlate another wide band file supported with zoom-band mode.”</div><div>A simple expression in the .v2d file is the comparison between:</div><div>(XXXXX and OOOOO are data with 2 GHz, and SSSSS is a data with the band of 256 MHz subtracted from XXXXX)</div><div>————————————————————————</div><div>ANTENNA G1</div><div><div>{</div><div> file = XXXXX.vdif</div><div> format = VDIF/8224/2</div><div> phaseCalInt = 0</div><div> addZoomFreq= freq@230000.00/bw@256.0</div><div>}</div></div><div><div>ANTENNA G2</div><div>{</div><div> file = OOOOO.vdif</div><div> format = VDIF/8224/2</div><div> phaseCalInt = 0</div><div> addZoomFreq= freq@230000.00/bw@256.0</div><div>}</div></div><div>———————————————————————— And,</div><div><div>ANTENNA G1</div><div><div>{</div><div> file = SSSSS.vdif</div><div> format = VDIF/8224/2</div><div> phaseCalInt = 0</div><div>}</div></div><div><div>ANTENNA G2</div><div>{</div><div> file = OOOOO.vdif</div><div> format = VDIF/8224/2</div><div> phaseCalInt = 0</div><div> addZoomFreq= freq@230000.00/bw@256.0</div><div>}</div></div></div><div>———————————————————————— </div><div><br></div><div>The loss in SNR or the amplitude is expected due to the re-sampling (FFT and IFFT for the original XXXXX.vdif) of the data, but we do not clearly understand the origin to cause the "possible shift" in the obtained phase distribution.</div><div>(We suspect the shift in phase is due to the adoption of the Ref. Freq., but the series of my tests cannot confirm this point.)</div><div><br></div><div>The motivation to do it is that we have limited/very slow internet speed in GLT. </div><div>In order to check the preliminary result via the obtained observation, we would like to send only the band reduced data with a much smaller file size.</div><div>So to investigate/handle the comparison between the aforementioned two cases is required for GLT team.</div><span class=""><div><br></div><div>Sincerely,</div><div><span style="font-family:新細明體,sans-serif;font-size:12px">--</span></div><div><div><div style="font-family:新細明體,sans-serif;font-size:14px"><span style="font-size:12px">Lupin Chun-Che Lin</span></div><div style="font-family:新細明體,sans-serif;font-size:14px"><span style="font-size:12px">Supporting Scientist of GLT (GreenLand Telescope) project </span></div><div style="font-family:新細明體,sans-serif;font-size:14px"><span style="font-size:12px">in Institute of Astronomy and Astrophysics, Academia Sinica,</span></div><div style="font-family:新細明體,sans-serif;font-size:14px"><span style="font-size:12px">14F of Astronomy-Mathematics Building (Rm: 1405), </span></div><div style="font-family:新細明體,sans-serif;font-size:14px"><span style="font-size:12px">National Taiwan University. </span></div><div style="font-family:新細明體,sans-serif;font-size:14px"><span style="font-size:12px">No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan.</span></div><div style="font-family:新細明體,sans-serif;font-size:14px"><span style="font-size:12px">Tel: <a href="tel:+886%202%202366%205464" value="+886223665464" target="_blank">+886-2-2366-5464</a></span></div><div style="font-family:新細明體,sans-serif;font-size:14px"><span style="font-size:12px">Fax: <a href="tel:+886%202%202367%207849" value="+886223677849" target="_blank">+886-2-2367-7849</a></span></div></div><div><br></div><br class="m_5095474439037212162Apple-interchange-newline">
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<br></span><div><div class="h5"><div><blockquote type="cite"><div>Adam Deller <<a href="mailto:adeller@astro.swin.edu.au" target="_blank">adeller@astro.swin.edu.au</a>> 於 2017年5月22日 上午8:15 寫道：</div><br class="m_5095474439037212162Apple-interchange-newline"><div><div dir="ltr" style="font-family:Helvetica;font-size:14px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;line-height:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">Hi Lupin,<br><div class="gmail_extra"><br><div class="gmail_quote">On 19 May 2017 at 13:22, Lupin Lin<span class="m_5095474439037212162Apple-converted-space"> </span><span dir="ltr"><<a href="mailto:lupin@asiaa.sinica.edu.tw" target="_blank">lupin@asiaa.sinica.edu.tw</a><wbr>></span><span class="m_5095474439037212162Apple-converted-space"> </span>wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div style="word-wrap:break-word">To the experienced user of DiFX or HOPS,<div><br></div><div><div>Sorry to spend you some time on two questions.</div><div>The first one is related to the integration time presented on the final plot after the auto- or cross- correlations.</div><div>(The DiFX I used is trunk ver. and and the HOPS ver. I used is 3.13)</div><div><br></div><div>1. </div><div>Here the GLT team recorded two signals with 3 noise sources (only 1 is the same with a potential delay less than 1 ns) from the same ROACH, and made a test in correlation.</div><div>We simply assumed that the Sky (Ref.) frequency is 230 GHz and the data were obtained from the same site (both G1 and G2 were assigned to the same position of GLT). </div><div>We correlated the data of 5-sec. supported with the zoom-band mode at 1,200-1,328 MHz.</div><div>————(Contents in .v2d file)———</div><div><div>vex = ext.vex.obs</div><div>mjdStart = 2017y124d05h42m00s</div><div>mjdStop = 2017y124d05h42m05s</div><div>antennas = G1,G2</div><div>startSeries = 7000</div><div>dataBufferFactor = 16</div><div>visBufferLength = 80</div><div>nDataSegments = 8</div><div>minLength = 0.5</div></div><div>————————————————</div><div>But according to the attached figure of “Zoom128_5sec.pdf”, the int time is only 4.995 sec.</div><div>What’s the reason to cause a loss of the obtained Int. time? </div><div></div></div></div><br></blockquote><div><br></div><div>This may be HOPS-related: I'm not an expert on HOPS so I can't comment. But another possibility is that the correlation runs from 054200 to 054205 at the geocentre, and if the recorded data duration was only 5 seconds long but at the telescope, then the geometric delay will mean than a few milliseconds of data will be chopped off. Maybe one of the HOPS users can chime in on how that integration time number is calculated in the HOPS plot - is it based on the weight? If so then my hypothesis is plausible.<br></div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div style="word-wrap:break-word"><div><div></div><div><br></div><div>2. </div><div>Following the previous test, I used Jan Wagner’s code to do the band subtraction (the original full band is 2GHz) and checked the obtained phase of different cases.</div><div>I summarized my tests and my questions in the attached file “phase.pdf”.</div><div></div></div></div><br><div style="word-wrap:break-word"><div><br><div></div><div>The 1st case is the same as shown in the attached “Zoom128_5sec.pdf”.</div><div>What’s the possible origin to cause the phase shift? </div><div>I originally suspect that such a shift is originated from the change in Sky/Ref. freq, but it might be wrong….</div><div><br></div></div></div></blockquote><div><br></div><div>I'm sorry, but I can't follow what your are trying to do here. I'm not sure what Jan's code is that you're referring to (is it something that filters e.g. your 2 GHz band down to 128 MHz in a chosen window?) If that is the case, what is the input - already quantised 2 bit VDIF data? That will lead to nasty re-quantisation errors - you'll notice that the amplitude goes down, too. <span class="m_5095474439037212162Apple-converted-space"> </span><br><br></div><div>But the root of the problem is: what are you actually ultimately trying to achieve? A verification of some kind?<br><br></div><div>Cheers,<br></div><div>Adam<br></div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div style="word-wrap:break-word"><div><div></div><div>Sincerely,</div><div><div><div style="font-family:新細明體,sans-serif"><span style="font-size:12px">--</span></div><div style="font-family:新細明體,sans-serif"><span style="font-size:12px">Lupin Chun-Che Lin</span></div><div style="font-family:新細明體,sans-serif"><span style="font-size:12px">Supporting Scientist of GLT (GreenLand Telescope) project </span></div><div style="font-family:新細明體,sans-serif"><span style="font-size:12px">in Institute of Astronomy and Astrophysics, Academia Sinica,</span></div><div style="font-family:新細明體,sans-serif"><span style="font-size:12px">14F of Astronomy-Mathematics Building (Rm: 1405), </span></div><div style="font-family:新細明體,sans-serif"><span style="font-size:12px">National Taiwan University. </span></div><div style="font-family:新細明體,sans-serif"><span style="font-size:12px">No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan.</span></div><div style="font-family:新細明體,sans-serif"><span style="font-size:12px">Tel:<span class="m_5095474439037212162Apple-converted-space"> </span><a href="tel:+886%202%202366%205464" value="+886223665464" target="_blank">+886-2-2366-5464</a></span></div><div style="font-family:新細明體,sans-serif"><span style="font-size:12px">Fax:<span class="m_5095474439037212162Apple-converted-space"> </span><a href="tel:+886%202%202367%207849" value="+886223677849" target="_blank">+886-2-2367-7849</a></span></div></div></div></div></div><br>______________________________<wbr>_________________<br>Difx-users mailing list<br><a href="mailto:Difx-users@listmgr.nrao.edu" target="_blank">Difx-users@listmgr.nrao.edu</a><br><a href="https://listmgr.nrao.edu/mailman/listinfo/difx-users" rel="noreferrer" target="_blank">https://listmgr.nrao.edu/mailm<wbr>an/listinfo/difx-users</a><br><br></blockquote></div><br><br clear="all"><br>--<span class="m_5095474439037212162Apple-converted-space"> </span><br><div class="m_5095474439037212162gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr" style="font-size:12.8000001907349px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px">!=============================<wbr>==============================<wbr>==!<br>Dr. Adam Deller </div><div dir="ltr" style="font-size:12.8px">ARC Future Fellow, Senior Lecturer</div><div style="font-size:12.8px">Centre for Astrophysics & Supercomputing </div><div dir="ltr" style="font-size:12.8px">Swinburne University of Technology <br>John St, Hawthorn VIC 3122 Australia</div><div style="font-size:12.8px">phone: <a href="tel:+61%203%209214%205307" value="+61392145307" target="_blank">+61 3 9214 5307</a></div><div style="font-size:12.8px">fax: <a href="tel:+61%203%209214%208797" value="+61392148797" target="_blank">+61 3 9214 8797</a></div><div style="font-size:12.8px"><br></div><div style="font-size:12.8px">office days (usually): Mon-Thu<br>!=============================<wbr>==============================<wbr>==!</div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></blockquote></div><br></div></div></div></blockquote></div><br><br clear="all"><br>-- <br><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr" style="font-size:12.8000001907349px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px">!=============================================================!<br>Dr. Adam Deller </div><div dir="ltr" style="font-size:12.8px">ARC Future Fellow, Senior Lecturer</div><div style="font-size:12.8px">Centre for Astrophysics & Supercomputing </div><div dir="ltr" style="font-size:12.8px">Swinburne University of Technology <br>John St, Hawthorn VIC 3122 Australia</div><div style="font-size:12.8px">phone: +61 3 9214 5307</div><div style="font-size:12.8px">fax: +61 3 9214 8797</div><div style="font-size:12.8px"><br></div><div style="font-size:12.8px">office days (usually): Mon-Thu<br>!=============================================================!</div></div></div></div></div></div></div></div></div></div></div></div></div></div></div>
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