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R: sun noise




----- Original Message -----
From: Nick Pugh <quadpugh@bellsouth.net>
To: <amsat-bb@AMSAT.Org>
Sent: Tuesday, January 01, 2002 9:24 PM
Subject: [amsat-bb] sun noise


> in an earlier post I left off the frequency and the system Noise Figure
> sorry for leaving out important details
>
>
> how much noise should you expect with the below listed perimeters
>
> ant gain 15 dbdc  db reference a dipole
> preamp .8 db
> system NF 1.2 db
> frequency 435 mhz
> SFU 42 e^-22
>
> happy new year nick k5qxj
>

Hi Nick, K5QXJ

Your ant gain is 15 dBdc dB reference to a dipole and since the gain of a
dipole is 2.14 dB over the isotropic antenna your antenna gain is
15 + 2.14 = 17.14 dBic or 51.8 time in power ratio

Your system overall NF = 1.2 dB and the equivalent noise factor is
 F=10 E(1.2/10)=1.31
The equivalent noise temperature of your system without antenna connected
is Tsys = (F-1) x 290= 92 kelvin

At 435 MHz the equivalent noise temperature of the cold sky is at best 30
kelvin depending on the side lobes of your antenna and so let say 50 kelvin
in your case.

When your antenna is pointed to the cold sky  the equivalent temperature is

Tsys (cold sky) = 92 + 50 = 142 kelvin

The figure given by you for the solar flux is sfu= 42
where the power of 1 sfu = 10 E -22 W/m^2/Hz

When your antenna is pointed to the sun the temperature Ta as seen by
the antenna alone can be calculated with good approximation using the
following formula:

          F x G x L^2
Ta= -----------------
              3.468

Where:
Ta = antenna temperature looking at the sun
F   = solar flux in sfu
G   = antenna gain as a power ratio (that is 17.14 dB = 51.8 )
L   =  wavelenght in meters (that is 435 MHz = 0.689 meters )
3.468 = is a constant

using the above data we compute:

        42 x 51.8 x 0.689^2
Ta=------------------------- = 298 kelvin
                 3.468

The system temperature with the antenna pointed to the sun is given by the
sum of :
Tsys(cold sky) + Ta  and so

Tsys ( antenna at the sun) = 92 + 50 + 298 = 440 kelvin

The (S/N)/N ratio that you should expect to receive from the sun
if you live in a quiet area with a very small man made noise much
 less than 50 kelvin is :

440/ 142 = 3  and so

(S+N)/N = 10 log     3 = 4.9 dB
                              10

4.9 dB of (S+N)/N provided the side lobes of your antenna are very well
attenuated and the sfu =42 is a correct value for 435 MHz

Since the above conditions of  low man made noise and small side lobes are 
unrealistics you are fortunate enougth if  your (S+N)/N= 2.5 dB and the
S meter barely move yes or not a half point or less.

The antenna polarization do not affect the received noise from the sun
because it is a random withe noise wich can be considered no polarized.

I hope this help

73 de i8CVS Domenico

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