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Re: SUISAT forensics...



At 09:13 AM 2/8/2006 +0000, Graham Shirville wrote:
>Hi Ed,
>
>Always up for a challenge, I have put some numbers into Jan King's fine link 
>budget spreadsheet. ........
>
>It indicates that the RF output level is not likely to be more than 10mW 
>maximum - probably somewhat less!
>
>You can download the standard spreadsheet from 
>http://www.amsat.org.uk/iaru/spreadsheet1.asp or if you would like to play 
>with the numbers I have used then go to www.shirville.com/anonymous.
>
>You will see that I have made a number of assumptions and that the programme 
>only displays one decimal place for the power - although it actually 
>calculates the 0.01watt correctly.
>
>73
>
>Graham G3VZV
>
>>
>> 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


Graham,

Thanks for your input.  Your spreadsheet is fairly involved to follow.
Also you used some data that differs from my example, above it seems.

I ran a simpler model:
Po = Pt - TL + Gant - L - Atmos
I borrowed 2.7 dB atmos loss from you
L = 32.4 + 10*LOG F + 10*LOG R

Pn = 10*LOG (KTsysB)
Tsys = Tsky + Tgnd + Trx
Trx = Tamb (10^NF/10 - 1)
Tamb = 273 + Tc
Tc local ambient temp in C
Prx = Pn - Grx

S/N = Po - Prx
S+N/N = S/N + 1
-----------------------------
TL = 2 dB
Gant = 2 dBi
F = 145.99 MHz
R = 1354 km
L = -138.3 dB
atmos = 2.7 dB
Po = -142 dBm

K = 1.38E-20
Trx = 48.5 K
NF = 0.74 dB
Tsky = 275 K
Tgnd = 40 K  [antenna G/T]
Tc = -12 C
Tamb = 261 K
Grx = 21.3 dBi  [four M2 2m-xpol-20]
Pn = -131.2 dBm
Prx = -152.5 dBm

S/N = 11
S+N/N = 12 dB  [from calibrated s-meter]

This implies that Pt = -0.5 dBm (rougly 1mw)  instead of the expected +27
dBm (500mw)

I guess that is close enough within the realm of round-off and other errors.
Obviously something has failed seriously in the Suitsat system
(battery/transmitter/cable connections???)
It actually amazes me that we hams can detect a 1mw signal from space.....eh?


73's,
Ed - KL7UW  
=========================================
http://www.qsl.net/al7eb - BP40iq 
144-EME: FT-847, mgf-1801/1402, 4xM2-xpol-20, 170w
432-EME: FT-847, mgf-1402, 1x21-ele (18.6 dBi), 60w
=========================================
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