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Re: FM vs SSB



If we assume an average efficiency of 80% for FM and 25% for SSB and AM then
the table for DC power input is:

 Unprocessed     Processed       RF
 Avg.    PEP    Avg.    PEP     BW      Mod.
 45      59      41      48       3      SSB
 45      59      41      48       6      DSB
 46      46      42      42       6      FM
 47      47      43      43      12     FM
 60      65      49      54       6      AM

AMSAT-DE pulished an article on HELAPS design many years ago and I beleive
that the peak efficiency (fully occupied transponder) was 50% and the
average was around 25%. Someone with a copy could check. The relative power
required from solar panels is in the average columns. PEP would approximate
peak current from the batteries.

73,

John
KD6OZH

----- Original Message -----
From: <k0vty@juno.com>
To: <kd6ozh@AMSAT.Org>
Sent: Saturday, July 26, 2003 13:48
Subject: Re: [amsat-bb] FM vs SSB


>
> John
>
> How about adding the DC power requirement the sun must furnish
> Or are you saying your current numbers cover that?
>
> Joe  K0VTY
> =================================
> --- "John Stephensen" <kd6ozh@gte.net> wrote:
>
> There is an extra "PEP" in the second line. The correct version is:
>
> Unprocessed     Processed       RF
> Avg.    PEP    Avg.    PEP     BW      Mod.
> 39      53      35      42       3      SSB
> 39      53      35      42       6      DSB
> 45      45      41      41       6      FM
> 46      46      42      42      12     FM
> 54      59      43      48       6      AM
>
> Transmitters are peak power limited so 6 kHz wide FM makes the best use of
> the power amplifier. If the object is to reduce the average power output
> then SSB wins.
>
> A speech processor is very useful on SSB as it reduces the peak power
> requirement by 11 dB. On FM you only gain 4 dB.
>
> 73,
>
> John,
> KD6OZH
>
> ----- Original Message -----
> From: "Mike Murphree" <mike@tropo.org>
> To: <kd6ozh@AMSAT.Org>
> Sent: Friday, July 25, 2003 14:23
> Subject: Re: [amsat-bb] FM vs SSB
>
>
> > > Here is some interesting data for transponder designers. The table
> > > compares the modulation types by the received signal level required
for
> > > an
> > > articulation index of 30%.
> > >
> > > Unprocessed     Processed       RF
> > > PEP     Avg.    PEP    Avg.    PEP     BW     Mod.
> > > 39      53      35      42       3      SSB
> > > 39      53      35      42       6      DSB
> > > 45      45      41      41       6      FM
> > > 46      46      42      42      12     FM
> > > 54      59      43      48       6      AM
> > > Source: Sabin & Schoenike, "HF Radio Systems and Circuits"
> > >
> > > The articulation index is the percentage of spoken words received
> > > correctly. The audio bandwidth in all cases is 300-3000 Hz. Processed
> > > speech is preemphasized by +6dB/octave above 500 Hz to prevent loss of
> > > the weaker high-frequency components in the human voice and then
clipped
> > > to a 7dB peak-to-average power ratio. The power levels are in dB above
> > > the receiver IF noise level in one Hz so that they are proportional
the
> > > power output at the transmitter regardless of receiver bandwidth..
> > >
> > > Note that narrowband FM requires the lowest peak power level. SSB
> > > requires the lowest average power level.
> >
> >
> > Looking at your table, isn't that reversed?
> > i.e. FM requires least average power, while SSB requires least peak
> > power...  and by definition FM peak power = average power.
> >
> > It also appears that using a speech processor on a satellite
> > may be a good thing as long as you back the power down to a readable
> > signal and not relative to some arbitrary value below the beacon.
> >
> > 73
> > Mike W4LNA
> >
> >
> >
>
>
> ----
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