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

*Subject*: Re: Fw: [amsat-bb] SUISAT forensics...The reverse procedure*From*: "Edward R. Cole" <al7eb@xxxxxxxxxxxxx>*Date*: Wed, 08 Feb 2006 20:01:39 -0900*In-Reply-To*: <01cf01c62d07$c90c8620$0201a8c0@tin.it>

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 ========================================= ---- 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

**Follow-Ups**:**Re: Fw: SUISAT forensics...The reverse procedure***From:*John B. Stephensen

**References**:**Fw: SUISAT forensics...The reverse procedure***From:*i8cvs

- Prev by Date:
**RE: AO-54?** - Next by Date:
**Re: AO-54?--reply by K7RR** - Prev by thread:
**Fw: SUISAT forensics...The reverse procedure** - Next by thread:
**Re: Fw: SUISAT forensics...The reverse procedure** - Index(es):