Saturday, 14 June 2014

Sun noise on 10GHz


I have temporarily mounted my 'old' Channel Master 90cm onto the EME mount, since I hadn't got round to reinstalling the 2.4m dish.


Using a standard Ku band LNB into my spectrum analyser at 1256MHz IF I was able to do some testing.
I now know that the correct elevation in between 23 and 23.5 degrees. I measured the max noise from the sun and then checked the angle that the elevation frame pointed and the elevation angle of the sun at that time according to VK3UM EME Planner. My measurements average just under 23.5 degrees. I later found that the Channel Master 1.2m dish shows 23 degrees. I suspect I am not far out!
I also noted that for maximum noise the shadow of the LNB saddle should be aimed at the base of the bottom tripod stay.

This is clearly shown in the second photo.
Anyway, the average sun noise to cold sky measured 7dB at a solar flux of 153. This compares with an indicated number of about 6dB using VK3UM EMECalc at 10.368MHz. I would expect a few tenths of a dB more at 11GHz.
Of course the VK3UM results depend on what assumptions you make!
In this case 0.65dB noise figure with no loss ahead of the LNB and the feed is a linearly polarised Chapperal three ring.
YMMV!

Sam

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