----- Original Message ----- From: "Michael Heim" [email protected] To: [email protected] 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 ARS KD0AR
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 sfu -22 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
http://www.swpc.noaa.gov/ftpdir/indices/DSD.txt
http://www.swpc.noaa.gov/ftpdir/latest/curind.txt
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% efficiency. 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