Re: Sun noise sanity check please


Rob, M0DTS
 

That's just reminded me that i did some tests on Saturday with my 10GHz system.

The LNA used is based on an lnb pcb and is ~1.0dB NF. 
Transverter is DB6NT G2 version.
Very short semi rigid coax between the lna and the relay.
There is an sma coax relay and 20cm piece of semi rigid coax between this and the feed.
The feed is G3PHO design and dish is a technomate 80cm (not sure of exact dimensions).
Sun noise vs nearby sky was quite repeatable at 3.9dB using sdr looking at 1MHz bw in sdr#'s measurement plugin.
I did not note the sfi though...

Hope its a useful comparison.

Rob
M0DTS


On Tue, 27 Aug 2019, 18:09 Neil Smith G4DBN, <neil@...> wrote:
I just measured 4.6dB of sun noise in a 10kHz bandwidth compared with a
patch of cold sky.  I can't make sense of the results I am seeing.

Setup is a 0.85 x 0.95 offset steel pierced dish with f/d about 0.6 and
a WA6KBL linear horn feed optimised for f/d 0.6

Waveguide feed about 1m total into a waveguide relay, then a Kuhne
waveguide EME LNA with 0.9dB NF.

I make the current 10.7cm SFI to be 67.  Putting that all into EMECalc,
I seem to be getting slightly better than the theoretical maximum, so I
must be doing something wrong. Ground to cold sky is about 2dB, although
I haven't integrated that for a long enough time.

I got very similar results from the SDR IF display and from my Fluke and
HP thermal millivoltmeters on the audio output.  ALso very similar when
I use the SDR calculation in SW2 to measure the time-averages noise
floor at 150kHz bandwidth (using the dBm/Hz value).

Is there somehting I'm doing wrong with EMECalc values?  Is the SFI
value not 67? The sun was behind thinnish clouds at the time, would that
mess things up wiht the measurements?

Key issue is that if I'm more than a dB or so worse than it should be,
I'll do more fiddling, otherwise I don't want to mess!

Neil G4DBN




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