[Difx-users] Lack of mixed-mode fringes with 2.6.3, then segfault with 2.8.1? {External}

[Eskil Varenius]

Dear Difx-users,

Background: I have mixed-mode continuum data from 3 stations: Ns(16 MHz VDIF), Ny(16 MHz M5B), Nn 32 MHz VDIF). Ns and Ny observe standard S/X with R-pol only, and Nn (VGOS) observe dual linear X/Y (strictly speaking H/V but I'm using X/Y here since that's the VEX labels). Correlating Ns-Ny baseline with DiFX 2.6.3, is all good. I use zoom windows (to get 16 MHz from all stations) and FreqId selection (to only correlate X-band and skip S-band channels). But when trying to correlate all three stations I run into problems.

Problem 1: With DiFX 2.6.3 I can correlate all three stations, and then run difx2mark4. Fourfit then gives me nice fringes on the Ns-Ny baseline (R-R pol), and the Ns-Nn baseline (RX and RY pol). But while I do get nice XR fringes on the Nn-Ny baseline, I do not get any YR fringes on this baseline. I know the data are good, since I get fringes to these polarisations on another baseline. So I suspect I have fallen into the "Warning: Limited support for mixed-mode..." here, or do you have other suggestions?

I saw there are improvements for mixed-mode in DiFX 2.8.1, so I decided to try it, but:

Problem 2: With DiFX 2.8.1, I get "segfault" when I run ”vex2difx” (this worked with 2.6.3). Any ideas?

I guess hunting the "segfault in 2.8.1" is the most profitable route for the future? If so, please let me know what info you may need to speculate further. I am happy to share output, v2d, vex, and even raw data for one scan for someone to reproduce this if you would be so kind to help.

I am very puzzled by this!

Kind regards
Eskil
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