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Re: Measure sun noise and AO40pass Re: Sun noise on Drake?



Chris,

I decided to run my program with your numbers.  With the 75K LNB gain of 65
dB it doe snot much matter what you run after it, as the LNB overwhelms all
NFs and cable loss after it.  Using your 3 KHz bw and 35 dB antenna gain
your system threshold is -178 dBm.  That should do very nicely for AO-40.
It should also work for eme.

Looking at sun noise and using 156 Jansky flux density you gave, if your
cold sky temp is 10K and antenna temp is 50K [Tsys = 75+10+50K], then you
should see 11.9 dB of sun noise.  This corresponds to a G/T = 20.9.

You do pretty good seeing 9.3 dB using the wide bw setting.    Your
measurement gives a G/T = 10.7, so apparently either one of our assumptions
is wrong or the flux density is not given at 2.4 GHz.  When I substitute 98
Jansky and an antenna temp of 80K,  the predicted and observed results
agree?  BTW I used a flux density of 98 Jy in the analysis I did for John
in the earlier post.  

Antenna temp. is a measure of how good your feed illuminates the dish [80K
is not too bad].  Most of the antenna temperature comes from dish
"spill-over", where the feed sees ground thermal noise.  I would guess for
hams that 10% would be an ultimate goal [10% of 290K = 29K].  It is also
possible that your cold sky reading is "polluted" with man-made interference!

I'm glad to see you show the change in sun noise at wider bandwidths.  It
is difficult to get good sun noise measurements using communication
receiver bw.  Most radio telescopes utilize bw of several MHz.  This is a
major difference between making celestial noise observations and obtaining
optimum communications performance.  Noise is usually of very wide spectral
nature.  Whereas narrow bw that match psk modulation is needed for good SNR.
Something else radio telescopes do to increase sensitivity, is to use long
sampling times [integration].

Thanks for sharing you observations
Ed


>From: "nn0v" <nn0v@home.com>
>I measured sun noise at 2.4ghz on a 9 foot dish I use for S C and Ku
>satellites.
>Equipment is a 75k LNB into an Icom R7100
>Sun noise:
>3k bw     7.5db -95dbm pointed at the sun at noon (el 41)
>15kbw    7.5db -87dbm
>150k bw 9.3db -75dbm
>Ant gain 35 db(9 foot)  and the losses are neglected due to the 65db LNB
>gain and the good performance of the 7100 at the 1250mhz IF.
>
>I recorded AO40 3-17-01 18:27z into a sound file but had the mixer switched
>to mic not line and did not get a sound file I can demod but it was hitting
>12-15db c/n
>at 15k bandwidth as it passed low to south, lots of PCS tower intermod
>when I point at south azimuths one of the phone towers, according to alon
>alat
>AO40 appeared on my reciever when squint went above 90 and range was
>7000 miles, and the slower spin rate its at now should help a bunch
>in telem capture.......today I noticed some other interference or effect
>that
>puts FM modulation on the converter so the telem may not have been
>any good even if I had it correctly recorded, but I just keep trying anyway
>cause its there and its interesting to figure out when it can and cant be
>heard.
>At this location I dont see any orbits where its squint gets above 145
>with 180 being ideal as I understand it. On its slower rotation that it has
>now there is still a super deep null it goes thru (maybe a circular feed
>would help eliminate this) at squint 95.
>
>but at max altitude the s-band antenna spends
>most of its time on the far side of the satellite so I dont expect telem
>unless
>its a low pass like this one where you got to drive the antenna and reciever
>like mad, or in the wee hours of the morning passes that I seem to sleep
>thru
>every time. Fun idea to test sun noise, now I have that measurement. Results
>may vary with sunspot activity and weather, the current solar flux reading
>is: 156 http://qrz.com/solar.html
>I still have the same old DRO downconverter out there but I am very
>interested in the taiwan made MDS converter someone was selling a bunch of,
>to get rid of freq drift. 125 meg IF would work fine with the R7100 since
>it gets everythng from 25mhz-2ghz....who is it that has em(all I need is the
>converter not the antenna) and I saw a price of $35.00 for them somewhere...
>I know it will work in demod because I have printed AO40 cleanly a few
>times with iz8bly which does an excellent job tracking the doppler
>especially
>when the AFC bandwidth is way up and the sync time is slower......but
>it still has trouble with the wild AM rotation modulation.
>
>See my web page to see what I am using now:
>http://members.home.com/nn0v/
>
>
>Too bad sunsat went off the air it was a fun little satellite.
>Worked it several times with just handhelds on omni when it flew over.




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