1420 MHz spectrogram update on system stability

David Lonard

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Apr 25, 2017, 10:27:14 AM4/25/17

to Amateur radio interferometry

I've installed 12th wave coax transformers in the 1420 MHz receiver system to improve stability. Still have temperature related issues, but I think the improvements are helping. I think I'm probably approaching the limit for what I can achieve in terms of stability in the absence of a noise reference.

transcoax.pdf

David Lonard

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Apr 25, 2017, 9:40:33 PM4/25/17

to Amateur radio interferometry

I've purchased some LMR-240 cable to replace the RG-6/U cable that I'm using now. It should have roughly ~10X better phase stability and a 12th wave 50:75 Ohm transformer wont be necessary. I hope that this will improve things. I've attached a link that describes the phase stability of different cables. When operating as an interferometer, the phase stability will be more important, so I hope this will be a worthwhile investment in the system. Stay tuned...

http://www.gb.nrao.edu/gbt/baseline/subpages/reports/MiscReports/cablePhaseStability.pdf

David Lonard

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May 8, 2017, 3:20:30 PM5/8/17

to Amateur radio interferometry

I've upgreaded to LMR-240 coax to connect the LNA to the SDR in the house. This has significantly improved system stability.

lmr.png

David Lonard

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May 9, 2017, 10:07:16 AM5/9/17

to Amateur radio interferometry

Now I've got the thermoregulation issues fixed for my LNA by having my thermoelectric cooler defending a higher temperature of 35 degrees C. Later in the summer, I will have to move up to a higher temperature most likely or reconfigure for 2 stage TEC cooling.

The TEC unit inside my house to thermoregulate a BladeRF had a fan failure which caused the BladeRF to overheat and it died. The posted results are from another BladeRF that isn't thermoregulated, although I keep the temperature in my house at a nearly constant 23 degrees C. Will have it thermoregulated better soon.

I've attached two images, one with very high contrast so that you can see the remaining instability and RFI. The other one is with a more 'typical' contrast setting. It is starting to look very nice indeed. Hopefully with multi-day integration, I will now finally start to see external galaxies. Stay tuned.

lmr2.png

lmr2b.png

David Lonard

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May 9, 2017, 4:09:11 PM5/9/17

to Amateur radio interferometry

Close-ups of the region with detectable neutral hydrogen signal.

Linear and log transformed.

lmr2c.png

lmr2d.png

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