[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: SUISAT forensics...



----- 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...


> >If we know exactly the 2 meters ground station antenna gain in dB
> >as well the overall noise temperature of the 2 meter receiving system
> >in degrees kelvin or alternatively we know it's overall Noise Figure
> >in dB than if we measure the ratio (S+N)/N of the received signals
> >in dB and we know the range at that time of measurement it is possible
> >to calculate with sufficient approximation how much ERP power
> >is present on Suitsat.
> >
> >Best 73" de
> >
> >i8CVS Domenico
> >----
>
> 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 Trx 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 to the above Noise Floor the free space attenuation of
138.35 dB 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 and if
I was not wrong.

Best 73" de

i8CVS Domenico
----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home