# RE: Question, FM on AO-40

• Subject: RE: [amsat-bb] Question, FM on AO-40
• From: "Gary Gonnella" <gary@xxxxxxxxxxx>
• Date: Thu, 23 Oct 2003 17:14:59 -0700

```>
> It is much higher - for narrowband FM alone it's 3K with no
> modulation, but
> when you have modulation you have a total bandwidth of 2 X the modulation
> plus deviation.  So (again for NFM) you have 2 X (3000 + 5000) =
> 16,000Hz.  And that is with no channel separation.
>

Thanks for the reply Emily. I am not trying to suggest that we use FM on
the bird just discuss what it would mean.
I understand that SSB has a considerably lower power density then FM.
However I don't Consider SSTV or RTTY as SSB. By this I mean that if you
have 100 watts PEP on SSTV it is continuous at this level, just as 100 Watts
PEP on an unmodulated FM is. So at this point there is no difference in
power level within the bandwidth. When the FM signal is modulated its
bandwidth goes up considerably but is power within its' respective bandwidth
is the same as the narrower SSTV signal. The power is spread over a wider
range making it harder to receive, but this is not the point now.

>
> Even with NFM channels of 16KHz, you will need additional guard
> frequencies
> which means you will be looking at a minimum of 25KHz.  So you can run 1
> NFM QSO at the cost of 8 SSB QSOs, 125 RTTY QSOs and goodness knows how
> many PSK31.

I have never operated AO-40 that I have not been able to find a 25Khz chunck
of the passband free.

>
> You will - an unmodulated FM signal is roughly pumping 4x the power as a
> fully modulated SSTV signal.  The numbers get ugly if you try to modulate.
>

unless I am missing something basic 100 watts PEP into SSTV or RTTY is the
same as 100 Watts on an unmodulated FM signal. Again this argument excludes
So unless someone can show me where I am wrong I will make the statement
that:
If I am in the bandpass with no signals within 20Khz either side of me and
my return signal is 10db below the beacon then I am not impacting the use of
the satellite any more that a RTTY or SSTV of equal power.

Gary Gonnella W6RYO
http://www.w6ryo.com

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