GNSS calibration project

Nov 5, 2020: we have set a date for initial test observations, friday Nov 13; some thoughts beforehand:

• We believe that we can do the measurements from the control room
• We will select a few suitable satellites (Lucia and Tiege) and use the TLE-RADEC satellite function for the 26m to actually track the satellite (Tiege looks into that – but we have used it previously)
• All we need for a start is a snapshot from the spectrum analyser over the transmission bands (L1 & L2)
• What we also need is a calibration of the antenna
• Once we have a few measurements, we can look into the formulas and try to derive the actual values that we need.

Nov 13, 2020: first tracking tests:

• setup: split off the multi-feed channel 1, nominally one of the linearly polarized ones; permanently installed; spectrum analyser connected of that; receiver multifeed 2 (L-band), agilent (1st LO) set to 4.1 GHz, 16 dBm output.
• spechb: on the network via vnc and socket connection; settings: input attenuation manually fixed at 10dBs; center freq and span adjustable; freq 500MHz, span 1 GHz; 100 counts average seems to look good by eye. video bandwidth of 10 MHz, resolution BW 3 MHz, sweep time 2.5 ms. (setup in automatic mode); narrower bandwidth allow better discrimination between RFI and signal; use different tracers; sky range 1.1 - 2.1 GHz;
• RFI: bruny island microwave link ~330MHz IF (1430 sky), mobile phones above 1.8 GHz, something at about 60-70 MHz (1160-70, blocking L5?)
• tracks: tracking using the satellite tracking module (sattrack); scheduled with 10sec updates.
• sattrack: satplt.pl window is the one to look at for current track; infos in spaceX_26m.pdf; has to be run on newsmerd; to stop: abort in vdesk window 3 - emergency: big red button

Nov 18, 2020: Tiege solo show:

• Spectrum analyser traces: When I got out here the spectrum analyser was not showing the expected spectrum despite L-band being on axis. Removing cable produced no change in the output, looks like after it was unplugged it needed to have the 'pre-set' button pushed (I think) in order for it to switch to the 'RF in' input. In the process of troubleshooting this I seem to have changed the behaviour of trace 1 and am not sure how to change it back to how it was. Trace 2 is still set to a 100 count average.
• Tracking testing: Testing the shell wrapper calling the 5 minute block schedules. All seems to run fine so far - Looks like it takes between 60s and 120s for the telescope to settle between schedule blocks - will need to take this into account for when we should be pulling from the spectrum analyser.
• Late start tracks: The current wrapper when run after the schedules start time will try each of the blocks in order until it finds one with a tracking point in the future - this is OK, but it takes a long time to iterate through all the previously observed blocks (~20s for each 5 min block - ~4 mins per hour of catchup). Not a big deal if you are only starting the track <1hr late, however, longer than this and you start to lose a significant amount of your observing time just catching up. Will need to look into a better solution for this - I have a solution which would work for python but need to look into what is possible in the shell script.
• Recording from spectrum analyser: I have written a very ugly script that currently grabs trace outputs from the spectrum analyser every 5 seconds during valid time periods (currently from 90s past the start of the scan to the end time). Between the 5 minute blocks it averages all grabbed spectra together and writes them to a file with the timestamp of the scan.

Nov 19, 2020::

• Late start tracks: The bash script generated during schedule generation has now been updated to include 'if' statements with time conditions - this should fix any issues with starting tracks late. Current version of the scripts can be found on my github in a repository named 'antenna_thrust_scripts' (https://github.com/tiegemccarthy/antenna_thrust_scripts) (Tiege)

Dec 2, 2020::

• Schedules Two tracks prepared for this day - one for KOSMOS 2461 (R735) and one for GPS IIRM-8 (G050) (Tiege)
• This day was cancelled due to high winds - had a meeting with Lucia, Jamie and Guifre instead. Tracking postponed until next week. (Tiege)

Dec 8, 2020:

• Another cancellation, this time due to post-LBA maintenance on the cryo system. (Tiege)

Dec 11, 2020:

• Remote track on GPS IIRM-8: fixed a few issues with the observing setup. First issue was time stamps in the shell wrapper not working on newsmerd - the date command was for some reason reading them as GMT+7 timezone despite the default output of date being in UTC. This has since been fixed. (Tiege)
• Also fixed a bug in the recording script that occasionally caused a type error when writing out the data with numpy.savetxt(). (Tiege)
• Wrote a script for doing manual (not scheduled) recording using the spectrum analyser - will be useful for when we need to calibration scans on quasars. (Tiege)

Dec 15, 2020:

• Draft observing guide: I have written a rough guide outlining the steps required in order to undertake the GNSS tracks and recording which currently exists on my google drive (Tiege)

Jan 21, 2021:

• GPS050 tracks: Finally have a run not being cancelled by weather. Running a full track of GPS050 today (and hopefully tomorrow pending weather) - trying a 3 degree offset on offsource scans as 1 degree was too little in our last run with valid data. Also trying some new spectrum analyzer settings - keeping RBW at 3 MHz and VBW at 10 MHz, but changing span to 999 MHz and sweep points to 333, this should remove the need to resample the data when reducing the data - should know by tomorrow. Ideally we will get another couple of tracks on this source next week to check experiment to experiment repeatability of the results.
• Flux calibration Assuming wind remains pleasant, will get some data on a couple of bright quasar sources - 1934-638 is a little too weak for our setup. Would also be good to get multiple sources so we can check SEFD estimations. Ended up getting a scan of 3C353. (Tiege)

Jan 22, 2021:

• GPS050 tracks: Have a full track from Yesterday and a few hours from today. Needed to extend offset to 4 degrees as 3 degrees still had evidence of both L1 and L2 signal in beam.

Jan 25, 2021:

• Script changes: Have changed the recorder to throw out traces from the spectrum analyzer that do not have the expected length - this simplifies data reduction as these traces would need to be removed prior to analysis normally.
• Data reduction: Track from Jan 21 has been reduced and didn't seem to have many issues (other than incomplete traces) - off source scans with the 3 degree offset still have signal in them and therefore power levels are underestimated. Jan 22 data seems to have a little bit of signal still in the band unfortunately - not sure if its worth going to 5 degrees. Something seems to have happened in the second half of the track on Jan 22 - looks like L1 and L2 signal disappear completely after a certain time. Perhaps there was a windstow I missed, I will check the logs on newsmerd.

TO DO:

• prepare tracks for 5 min on source off source (for 1 satellite at a time); probably try 1 sec updates; how does sattrack handle this? code up 5 minute tracks to load after each other (run in sequence) - after the track finished, the antenna sits at the final az/el
• define spectral analyser output - pulling & scripting seems to work - but what and how long to write out data?; question what resolution and freq span? Why is TRACE output always 500 points? https://cdn.rohde-schwarz.com/pws/dl_downloads/dl_common_library/dl_manuals/gb_1/f/sfl_1/FSL_OperatingManual_en_12.pdf
• SEFD calibration - need to work out how to do this? VirgoA or Hydra is strong - use on/offs and spec an. Nominal SEFD about 400-500 Jy
• define an output from the spectral analyser - a dataset that we can work on; do some tests regarding resolution etc
• try repeatability - observe the identical satellite for 3 days in a row and compare values
• get value table ready - try to replicate the tracking table Peter Steigenberger sent through; figure out boresight angle etc (Lucia to ask Ron/Peter)
• have a look at subsequent estimation - get all the necessary values together, code an estimator? first understand the code
• next track: booked in next Wednesday (Nov 18) for more tests
• next catchup: booked in Wednesday (Dec 4)