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Fw: SUISAT forensics...The reverse procedure



----- Original Message -----
From: "Edward R. Cole" <al7eb@acsalaska.net>
To: "i8cvs" <domenico.i8cvs@tin.it>; "Luc Leblanc VE2DWE"
lucleblanc6@videotron.ca>; "AMSAT-BB" <amsat-bb@amsat.org>
Sent: Wednesday, February 08, 2006 7:55 AM
Subject: Re: [amsat-bb] SUISAT forensics...

>OK here are some numbers to crunch:
>My observations of Suitsat at approx 1104utc 4Feb.
>signal S+N/N = 12 dB  (3 s-units over noise floor)
>system NF = 0.74 dB
>antenna gain = 21.3 dBi (vert-pol)
>range at closest approach = 1354km
>FM mode (15KHz BW)
>elevation angle = 9 deg
>Tamb = -12C

>Have fun!
>73's,
>Ed - KL7UW

Hi Ed, KL7UW

I have worked out your numbers as follows:

Your signal (S+N)/N = 12 dB = 15.84 in power ratio so
your S/N= 10 log    (15.84-1) = 11.71 dB
                            10

Your system Noise Figure NF= 0.74 dB and so your Noise Factor F
is
           (10/0.74)
F= 10                  =  1.185  in power ratio and the equivalent noise
temperature of your RX is Trx= (1.185-1) x 290 = 53.65 kelvin

Your antenna gain = 21.3 dBi

Your range of closest approach with Suitsat = 1354 km

Your RX Band Width  (BW) = 15 kHz = 15.000 Hz

We can compute the free attenuation L between you and Suitsat

L = 32.44 + 20 log     145.99 + 20 log    1354 =  138.35 dB
                                10                           10

We assume that the equivalent noise temperature Ta of your antenna
is Ta= 1200 kelvin including the thermal noise picked up from the cold
sky plus the thermal noise picked up from the side lobes looking at
the ground so that the power Psys of Noise Floor referred to the input
of your RX when the antenna is connected can be computed as follows:

                                         -23
Psys =10 log   [ 1.38 x 10    x ( 53.87 + 1200 ) x 15000 = - 125.85 dBm
                      10


Adding to Psys the antenna gain of 21.3 dB is like to reduce the Noise Floor
at the input of  your receiver by 21.3 dB so that we have - 147.15 dBm

If we subtract the free space attenuation of 138.35 dB to the above Noise
Floor we get the EIRP necessary for Suitsat to be received on the ground
with a signal to noise ratio S/N= 0 dB or with the signal equal to the noise
for a range of 1354 km so that

-147.15 + 138.35 = -8.8 dBm   is  the EIRP of Suitsat for a S/N = 0 dB = 1

Since you receive Suitsat with a S/N= 11.71 dB this implies  that the
EIRP of Suitsat is -8.8 + 11.71 = + 2.91 dBm and

                                                         (10/2.91)
                     EIRP of Suitsat =  10                  =  1.95 mW

about 1.95 mW considering all round off and all unknown effects
                                          --------------------------------

Here the reverse calculation procedure starting from Suitsat coming
down to the ground station using your data and the computed data:

Computed Suitsat EIRP........................+2.91 dBm

Isotropic free space attenuation
over 1354 km...................................  - 138.35 db
                                                             ---------------
Available power in to an isotropic
ground antenna.................................. - 135.44 dBm

Receiving antenna gain.......................+ 21.30 dB
                                                             ---------------
Available input power of ground
receiver ...............................................- 114.14 dBm

Computed RX Noise Floor with
antenna connected.............................. - 125.85 dBm
                                                              --------------
S/N ratio at receiver output.............. +  11.71 dB


Using your data and having already calculated the Suitsat EIRP to be
+ 2.91 dBm  = 1.95 mW the above inverse procedure demonstrates that if
your measured data are correct than it is correct that your S/N had to be
11.71 dB

Best 73" de

i8CVS Domenico
----
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