[amsat-bb] FW: [FWD: RE: Southern CA Satellite Presentations]
jim at k6ccc.org
Tue Jun 28 15:33:50 UTC 2016
Jerry Conner said (in part):
> I have a hard time with all the purest, my way or the highway mentality
I am hearing.
It's not that it's a elitist mentality, it's simply a technical
requirement for successful operation. Even on a FM satellite, operating
without full duplex would be about like trying to use your local 2M
repeater with a transmitter and no receiver turned on until AFTER you
called someone. You have no way of knowing if someone else is talking.
Since on most FM satellites, the idle time between conversations is
measured in milliseconds, your chances of successfully hitting an idle spot
without knowing if your are getting through is quite slim. On SSB or CW on
a linear satellite, without full duplex, you will forever be chasing trying
to figure out where your downlink is. Even with complete computer control
of dopler shift, you will still be chasing the other guy.
On an FM satellite, the situation goes something like this. A contact
ends, and for example three people key up to make a call at essentially the
same time. Depending on signal levels, maybe one person has a strong
enough signal to capture everyone else, but more likely there is a massive
hetrodyne between several signals. With everyone operating full duplex,
we all hear that either someone else is capturing the uplink or the
hetrodyne and drop carrier. If you're not using full duplex, you blindly
keep transmitting and creating interference for the rest of the users.
The exception to all this is that if you are operating in a location that
has almost no one to talk to (Hawaii comes to mind) since you are almost
the only one around, you might get away without full duplex most of the
time. A decade or so ago, every night there was a SE to NW pass that was
well off the southern California coastline - such that the footprint only
covered 50 - 100 miles along the coast. There were a small enough number
of us in the footprint that we could actually hold several minute
conversations with one or two other people. Non full duplex would likely
have worked in that case. However for the previous pass that covered most
of the US, I would not have even considered it.
BTW, note that in my first sentence, I said "it's simply a technical
requirement for successful operation." The key word there was successful.
Without full duplex you will occasionally make a contact (especially as
mentioned earlier if you are almost the only person in the footprint), but
if you want to routinely be successful on busy passes, there is no
alternative to being full duplex. Period.
Jim Walls - K6CCC
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