[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Re: [sarex] SSTV in Violation [???]



While I take no sides in the bickering, the understanding of FM carrying
SSTV needs to be worked on a little.  The SSTV is an FM'ing AUDIO SUBcarrier
which is then FM modulating a carrier.   The is the like the AFSK used by
Bel-202 modems on VHF/UHF everywhere.  The point of using
FM to carry the FM subcarrier is that it is EASIER to track, not harder. That
having been said, once the signal is moved to 70 cm, it will be quite difficult
to track without a computer controlled radio unless
you are using a frequency offset indicator.  Not because it is FM but because
the filters in the FM receiver will not be sufficiently broad to receive the
signal from AOS to LOS, horizon to horizon and most handhelds having no tuning
indicators to show you average carrier offset.  The doppler will be large on 70
cm but it does not need to be tracked as tightly as (say) 1200 bps PSK from
AO-16.  You should be able to do this manually with an HT (say) once you have a
little practice.  It is the lack of tuning aids on the HT that will make it
difficult,
not the very fact that it is an HT or that it is FM.  The signal itself should
be booming enough to easily overcome the double threshold effect
of FM'ing subcarrier, FM'ing the carrier on all but the meekest of
lash ups.

John Mock wrote:
> 20-25 KHz during a pass.  I don't know much about SSTV modes, but if
> the baseline is FM, one has to track doppler alot more carefully.  Yes,
> you can do it by ear (that's how i worked the MIR/SAFEX repeater), but
> it is not a mode for beginners.  Allowing folks to try out beginning-
> level decoding on 2 meters seems to be to me an excellent idea. And if
> the timescale is a few weeks rather a few days, that may not be so bad;
> let's just not look at months.  (Unless they're turning on the SAFEX
> Repeater at the same time, to give the rest of us something to do.)
> 
>                         -- KD6PAG  ("Networking Old-Timer, RF newbie")
> 
> ----
> Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home