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Re: Fw: SUISAT forensics...The reverse procedure



Domenico,

You, Tony AA2TX, and David G0MRF have all arrived with numbers near the
same and mine.  I think that assures that the apparent signal is in the low
mw range and absolute accuracy is not really meaningful since S-meter
readings can not be precisely peaked (taken quickly in real-life situations).

I do differ in a couple places in the analysis so I will mention them.
There really is not point in debating them a lot.

For Tsky I chose 275K as reasonable quiet sky temp at 144-MHz.  It probably
is somewhat higher due to the horizon being in the antenna main lobe since
elevation was only 9-degrees.  That would only raise it to 290K.  I chose
Ta = 40K as this is a very well designed eme array.  G/T = -2.68.  I think
1200K is too high, and I live in an area without man-made industrial RFI to
contribute to this.

I calculated my Trx based on an ambient temp = -12C (261K) so I had Trx ~
46K, but who really cares as we were looking for a magnitude of transmitter
ERP not high accuracy (consider the receiver signal measurement accurracy
as limiting).

So I am came out with 1mw and you 2mw.  I think we agree that the power
level is in the single digit mw's which is considerably below that expected
(500mw).

Thanks for confirming my analysis.  I always learn a little by looking at
the results produced by others.

73's Ed - KL7UW


At 12:31 AM 2/9/2006 +0100, i8cvs wrote:
>----- 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
> 
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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