[amsat-bb] Re: sun noise and other natural noise sources

i8cvs domenico.i8cvs at tin.it
Wed Sep 3 11:03:04 PDT 2008

----- Original Message -----
From: "Michael Heim" <kd0ar at sbcglobal.net>
To: <AMSAT-BB at amsat.org>
Sent: Wednesday, September 03, 2008 2:06 AM
Subject: [amsat-bb] sun noise and other natural noise sources

> I am working on an S-band receive setup.  I currently operate X band
> terrestrial, and used sun noise as a test of my receive equipment there.
> It is quite weak on 10 GHz.  Noise from the earth (aimed at the ground) is
> many times stronger.  Aiming at trees, buildings, etc produce substantial
> noise on 10 GHz.  The question I have is... Can I use the same techniques
> on 2.4 GHz?   Of course antenna gain is lower, but noise figure should
>  be fairly close - 1dB or so....
> I have 2 units for 2.4 I'm testing.  one has an integral yagi antenna,
> supposedly about 16dB gain.  The other has an N connector, of which I have
> not designed an antenna for it yet.
> So, the question is... is sun noise stronger, weaker on 2.4 than on 10
> ghz?  If equipment is functioning properly should I be able to detect the
> sun?  I actually didnt think about trying to hear a tree on it, but they
> should also be noise sources on that band as well.
>  Michael Heim

Hi Michael, KD0AR

The Sun radiates uncoherent energy into the radio spectrum in form of
withe noise and the power of it is measured in Solar Flux Units i.e. in
One sfu is equivalent to a power of 10     watt / square meter / Hz
incident over the aperture area of your antenna and 1 sfu is 10.000 time
greater than the radio flux unit Jansky used by radioastronomers.

The energy radiated by the Sun is direcly proportional to the frequency
and infact if you look at the following pages



you will find that at the same time 04:00 UTC of day 3 september 2008 the
value of sfu measured by the NOAA stations in Learmonth and Penticton was

66    sfu at 2800  MHz
233  sfu at 8800  MHz
522  sfu at 15400 MHz

indicating that the energy in watt for each square meter and for each Hz of
bandwidth radiated by the Sun increases increasing the frequency.

We amateurs we refere our calculations to the frequency of 2800 MHz or
10.7 cm tanks to W8MIF wich converted the sfu at 2800 MHz into all
corresponding values of sfu for the amateur bands of 1296-2304-3456-5760
and 10368 MHz as reported by an article written by Bob Atkins KA1GT
into the ARRL UHF/Microwave Experimenters Manual ARRL order Nr 3126

In addition tanks to Melvin WR0I of the North Texas Microwave Society we
have the software NOISE.EXE

Using it directly with the sfu at 2800 MHz we can easily calculate the
expected  Sun Noise for 9 amateurs bands from 144 MHz to 10 GHz

Supposing that your 10 GHz dish has a diameter of 60 cm with a gain
of 33 dBi at 50% efficiency with an antenna temperature Ta= 10 kelvin
due to side lobes and spillower looking at the ground and a receiver with
an overall Noise Figure of 1 dB  so that Te=75 kelvin then your System
Temperature Tsys = 75+10 = 85 kelvin
Since the Sky temperature at 10 GHz is 5 kelvin with 66 sfu at 2800 MHz
today NOISE.EXE says that you should receive a Sun Noise of about
4.4 dB at 10 GHz

Going to 2.4 GHz you says that your antenna has a gain of 16 dBi
corresponding to the gain of a dish of about 40 cm or 15.7 inch at 50%
The antenna temperature Ta at 2.4 GHz for a dish of that size is at best
about 70 kelvin and since the overall Noise Figure of your receiving system
is 1 dB then Te= 75 kelvin and the System Temperature  Tsys=75+70=145 kelvin
The Sky temperature at 2.4 GHz is about 50 kelvin so that to day with
66 sfu at 2800 MHz NOISE.EXE says that at best your Sun Noise is only
0.3 dB

By the way in a separate message I have sent to you NOISE.EXE and several
other related papers so that you can play with it "all night"

Have fun and 73" de

i8CVS Domenico

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