Changing coaxial cable on Solar Cooker Radio Telescope at LRO 2/1/2025
My son and I have changed the coaxial cable on my 1.5m parabolic solar cooker radio telescope from 5m of RG58 coaxial cable to similar length of LMR400 coax and – wow! The signal strength shot up dramatically, the signal was far smoother and RFI seemed to be less of an issue instantly!!!
Mind you, the coax cost more than the parabolic dish…….
So the parabolic solar cooker radio telescope (LRO-H2) now consists of:
1.5m parabolic dish5m of LMR 400 coaxial cable –> WT Microwave 1420MHz+/-2MHz cavity filter –> Nooelec SAWBird H1 LNA –> computer.
Software
Currently, I am collecting data on this telescope using SDR#/IFAverage plugin (I have eventually got around the testing the setup using this software, Alex!).
Will be interesting to see whether the output is better or not with new coaxial cable and very narrow band filter.
Can anyone comment on whether the 2 x filters should be:
(i) 1.5m parabolic dish5m of LMR 400 coaxial cable –> WT Microwave 1420MHz+/-2MHz cavity filter –> Nooelec SAWBird H1 LNA –> computer.
(ii) 1.5m parabolic dish5m of LMR 400 coaxial cable –> Nooelec SAWBird H1 LNA –> WT Microwave 1420MHz+/-2MHz cavity filter –> computer.
Andy
Your LNA needs to be right up at the dish feed:
Dish-feed->LNA—>coax—>filter—>receiver—>computer
5 meters of LMR-400 has a loss of almost 1 full dB at 1420MHz–that translates to an extra 70K of additional Tsys if that much
cable is *in front* of your LNA.
Similarly, filters will have an insertion loss, and typically that insertion loss goes up as the bandwidth becomes narrower.
My guess is that your narrow-band filter has a loss above 1dB, so another 70K of additional Tsys.
The order that I describe above is what one would expect. The only thing that could be an issue is that you might still
need that narrow filter *in front* (ugh!) of the LNA to keep it operating linearly in a heavily RF-polluted environment.
Thanks Marcus. I am going to change over to the arrangement you recommend.
Andy