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*Subject*: R: [amsat-bb] Downlink budget calculation*From*: "i8cvs" <domenico.i8cvs@xxxxxx>*Date*: Thu, 1 Jul 2004 01:56:59 +0200

----- Original Message ----- From: Joel R. Stanley <j_r_stanley@wyan.org> To: <amsat-bb@AMSAT.Org> Sent: Wednesday, June 30, 2004 8:57 PM Subject: [amsat-bb] Downlink budget calculation > Hello, > > I'm trying to calculate how much gain (from the antenna and preamp) I > need for satellite reception. > > We have the link budget equation Prx = (Ptx + Gtx) + Grx - Afs - Am, > where Prx is the received power (dBW), Ptx + Gtx is the EIRP (dBW), Grx > is the receive gain (dBi), Afs is free-space attenuation loss (dB), and > Am is miscellaneous loss (dB). My receiver specifications state that > its sensitivity is "better than -15dBu for 12dB S+N:N". > > Okay, a dBu is dB relative to one microvolt. How does this relate to > Prx in dBW? If I take that -15 dBu, and convert to volts, then > calculate power assuming 50 ohm impedance (V^2/50) and convert that to > dBW, is that the correct value to use to find Grx? > > Thanks and 73 de Joel KC8DQH. > Hi Joel, KC8DQH One microvolt attenuated by 15 dB or -15 dBuV is corresponding to (-15/20) -6 10 = 0,177 uV = 0,177 x 10 = 0,000000177 volt Assuming 50 ohm the input impedance of your RX and assuming that the above voltage is the applied voltage needed by your RX to receive a signal with a ratio (S+N)/N of 12 dB than the power applied to the input of your receiver must be 2 -16 P= 0,000000177 / 50 = 6,26 x 10 watt and hence -16 10 log 6,26 x 10 = -152 dBW or -122 dBm 10 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 ---- 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: Downlink budget calculation***From:*John Santillo

**References**:**Downlink budget calculation***From:*Joel R. Stanley

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