• Subject: R: [amsat-bb] Downlink budget calculation
• From: "i8cvs" <domenico.i8cvs@xxxxxx>
• Date: Thu, 1 Jul 2004 13:43:24 +0200

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----- Original Message -----
From: John Santillo <u1004467@warwick.net>
To: i8cvs <domenico.i8cvs@tin.it>; Joel R. Stanley <j_r_stanley@wyan.org>;
AMSAT-BB <amsat-bb@AMSAT.Org>
Sent: Thursday, July 01, 2004 4:38 AM
Subject: Re: [amsat-bb] Downlink budget calculation

> Interesting thread but I have a few more questions.
>
> If the signal at the receiver's input must be at least -122dBm to be
"heard"
> by the receiver, then what is the assumed bandwidth?  Is it for voice, CW
or
> data?  Won't CW be about 5dB better than SSB with the same power at the
> input?
>
Hi John, N2HMM

I believe that the sensitivity specifications of -15 dBuV for (S+N)/N= 12 dB
given by Joel KC8DQH for his receiver are for SSB and so they are for a
filter BW = 2.5 KHz and this is the case of an FT-736 for example.

In this condition if the applied SSB input signal is -122 dBm it will be
heard "by the receiver" with a ratio (S+N)/N = 12 dB

If you tune a CW signal instead of a SSB signal without changing the
at all but a CW signal is always better discernible over the noise than an
SSB signal and how much better depends by the phisiological capability
of your ears because there are CW operators in condition to copy Morse
code about 20 dB under the noise and other that are not in condition to
detect CW with a signal=noise

CW than switching from SSB to CW the noise floor will be better (less) by

10 log   (2500/500) = 7 dB
10

In this conditions the above receiver will get available at the output a CW
signal with a ratio (S+N)/N = 12 dB with only -122-7 = -129 dBm at the
input

> Assume for the moment it's for voice and the filter bandwidth is 2.5KHz
then
> can an operator actually understand what is being said at -122dBm or do
you
> need another 6dB or so to make the voice discernable.
>

In this case if the filter BW is 2.5 KHz and the applied signal is -122 dBm
than the above receiver will get available to the operator an SSB signal
with a ratio (S+N)/N = 12 dB

> '73,
>
> John
> N2HMM
>

73" de

i8CVS Domenico

>
> ----- Original Message -----
> From: "i8cvs" <domenico.i8cvs@tin.it>
> To: "Joel R. Stanley" <j_r_stanley@wyan.org>; "AMSAT-BB"
> <amsat-bb@AMSAT.Org>
> Sent: Wednesday, June 30, 2004 19:56 PM
> Subject: R: [amsat-bb] Downlink budget calculation
>
>
> >
> > ----- 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
> >                               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
> >
> >
>
>

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