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RE: RE: Geo Opportunity FM vs SSB



Here is a new approach to the FM single channel versus SSB linear
transponder tradeoff.  I think many discussions fail to  consider the
widely different potential "applications".  For example, if one does not
bog down in weak signal argements and is concerned with passing
meaningful information via a given channel comfortably, I think FM wins.

Given that we have AO-40 continental weak signal transponder, that can
support many users, I'm still considering the totally different possible
Amateur Radio application of a single "clear" FM channel for special
applications.  (for the same DC power).

I'd really like to fully figure out this table:

PARAMETER        FM                       Linear (SSB)
--------------   -----------------------  -------------------
BANDWIDTH        12 KHz                   3 KHz
SNR improvement  Great above Knee         1:1 improvement
Weak signal      Poor below Knee          good
DC power         constant                 lower average power
Peak power       same, constant           Higher PEP
Users            1 at a time STRONG       many (weak)
Hardware         Class C, plug-n-play     extreme care to linearity
Contention       FM Capture effect        Pumping AGC competition
viability        You have it or not       Variable on # of users
USAGE            HIgh articulation index  poorer articulation index
                 Good arm-chair copy      noisy signals
                 comfortable listening    not comfortable after a while
                 Good Traffic handling    not as good

So, it seems to me that for a given DC power available, that it boils down
to supporting multiple weak-sginal DX or supporting one stronger, clearer
FM quality signal.  The two have totally different applications.   Chasing
DX (ala UO-14) is a perfectly wrong way to use an FM transponder.

Operating a NET with a NET control like any useful traffic handling net is
an example of a RIGHT way to use a clear FM channel.

Besides, I can understand the "thrill of the chase" of DX via all the
variable propogation modes on HF where the reward is a measure of the
skill and the rare conditions.  I dont see the same quality of experience
when the weak signal path is through a GEO bird that is ALWAYS THERE.
I think we should consider using a bird that is "always there" in kind of
the same way we use the ACARS net or the MARITIME MOBILE nets.  Or any of
the permanent HF nets...  or like we use the AMSAT net on AO-40.

Imagine if that were an FM channel...

So there are lots of trades in this comparison...  the answer is not as
clear cut in my mind as some people seem to argue... Remember, my design
would have a private separate FM uplink channel for the NET control which
has priority over the "net" channel, so that he can maintain complete
control.

de WB4APR, Bob

GEO Opportunity:   http://www.ew.usna.edu/~bruninga/supergeo.html



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