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Re: AO-40 data mode



Yup, I agree but for a ham radio mode will we be able to turn our ICOM's and 
Yaesu's around in time (even in full dup mode, the synths have to lock on a 
TX keyup) to shut off the modems on a silent time?  Probably not.  So, at 
least for a initial "soundcard" application we are stuck transmitting the 
silence.

But if it caught on, then a TDMA type system could be the next step... with 
custom radios, etc.  Direct QPSK modulation at 435 or 1269 is definately 
possible and could be switched VERY fast.

Fred



>From: "Louis A. Mamakos" <louie@TransSys.COM>
>To: "Frederick M. Spinner" <fspinner@hotmail.com>
>CC: emily@emilyshouse.com, amsat-bb@AMSAT.Org
>Subject: Re: [amsat-bb] AO-40 data mode Date: Thu, 23 Oct 2003 19:57:15 
>-0400
>
>
> > 3. I don't understand why you think you'd need 3dB more power?  Than 
>what?
> > SSB?  The only disadvantage to digital modes is that silent parts of 
>speech
> > still takes ones and zeros to get across, but on the other hand, the 
>peaks
> > in SSB would be higher.  Averaged out, the FEC'ed digital signal should 
>take
> > less spectrum and power than the SSB voice.  It's mathematical magic, 
>yes,
> > but true.
>
>Many (some?) narrowband voice CODECs perform silence detection and send
>no frames during silent periods.  In most applications using digitized
>voice, one of the other major factors that's managed is the latency
>(which related to frame sizes), and also how sensitive the CODEC is to
>delay jitter in the arriving frames.  The jitter issue can be a pain on
>a packet-switched network, but on a point-to-point RF links (bent in
>the sky or not), the jitter should be essentially zero, with small,
>regular changes due to the change propagation path.
>
>louie
>
>
>
>----
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