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Subject: Re: My Spread Spectrum Letter to FCC
Date: Sat, 30 Nov 1996 22:00:13 -0500
The possibilities for very low erp eme are (at least at first look) as
stated in one of greg's notes. Lower the data rates (equal to that
accomplished with low speed cw), let a 500Khz spread rip, and (with no
interference) you may end up with 40+ db useful process gain.
The problem lies in the occupancy of that 500KHz part of the spectrum,
especially if its on 2 mtrs (or even 70cm). Put several of these stations on
trying to work eme in the same 500 KHz (probably the lower end of 2 mtrs) and
all of a sudden that 40+ db gain isn't enough. No problem you say, just be
sure you are using a code orthogonal to everyone else. Sorry, -20db is close
to the real world equipment/propagation limit of crosscorr. FDMA (even TDMA)
of narrow band signals still allow a larger number of stations to operate on
a band segment in a common geographical area (their almost all in a common
area when on eme).
As for use on 220 and/or 902, SS may be the preferred route (select uwave
bands also offer sufficient room). But for most of 6, 2, if not a large
portion of 70cm, the FDMA of narrowband emitters is still the most efficient
approach for weak signal operations over much (possibly most) of the country.
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