Tom Bruhns wrote:

W7WKR was doing some experimenting in that area a few years ago (w/FCC
permission), and likely would share some info. I don't have his email
address handy, but perhaps you can find it with a search.

Since very accurate time is available, it should be possible to get
close in the sequence. A typical way to lock onto pseudorandom things
is through correlation. But how do you optimize things when there's
fading and very weak signals to begin with?

Well, the nice thing about spread spectrum is that it effectively
integrates all that under-the-noise signal and produces something with
a lot more amplitude. And yes, the autocorrelation properties of the
PN sequences are very important in synchronization: the output of the
correlator is something close to 1/n for out-of-sync and 1 for in-
sync.

The difficulty is knowing roughly where in a long sequence to start
the search, and that's why the military GPS receivers use the C/A
(Coarse Acquisition) signals to get the Precise Positioning Service
parts of the receivers in the ball park. Once they've done that, it's
the same old game: slew the clock and look for a jump in the output of
the correlator.

--
Mike Andrews

Tired old sysadmin, math jock very much interested in SS

A company I used to work for manufactured a frequency hopper spread
spectrum unit.

It was a 'slow' hopper, with Ack/noack for packets so it would retransmit
a missed data packet which covered the case when a particular channel was
occupied.

The acquisition method would also work for a pretty fast frequency hopper
too. It used a master unit that sent a sync signal burst every time it
jumped to a new channel. The remote that was looking for the master would
jump in a duplicate pattern, but at a slower jump rate until it heard the
sync signal from the master. the remote would then start hopping at the
correct rate, and follow the master as it hopped.

Acquisition might be a bit slow, but it did work nicely, and it allowed
other remotes to be turned on at any time and acquire the network.

==============

I have never tinkered with an amateur radio version, but it seems to me
that the ARRL has a book on spread spectrum and there are some FCC mandated
requirements for the PN code, or the hopping pattern for freq hoppers, to
allow the FCC to be able to listen in.

The FCC also limited which frequency ranges Spread Spectrum can be used
on, so I'd do a bit of digging before trying to build hardware......



Jim Pennell
N6BIU

A company I used to work for manufactured a frequency hopper spread
spectrum unit.

It was a 'slow' hopper, with Ack/noack for packets so it would retransmit
a missed data packet which covered the case when a particular channel was
occupied.

The acquisition method would also work for a pretty fast frequency hopper
too. It used a master unit that sent a sync signal burst every time it
jumped to a new channel. The remote that was looking for the master would
jump in a duplicate pattern, but at a slower jump rate until it heard the
sync signal from the master. the remote would then start hopping at the
correct rate, and follow the master as it hopped.

Acquisition might be a bit slow, but it did work nicely, and it allowed
other remotes to be turned on at any time and acquire the network.

==============

I have never tinkered with an amateur radio version, but it seems to me
that the ARRL has a book on spread spectrum and there are some FCC mandated
requirements for the PN code, or the hopping pattern for freq hoppers, to
allow the FCC to be able to listen in.

The FCC also limited which frequency ranges Spread Spectrum can be used
on, so I'd do a bit of digging before trying to build hardware......



Jim Pennell
N6BIU