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

----- Original Message -----
From: "Laura Halliday"
Newsgroups: rec.radio.amateur.homebrew
Sent: Tuesday, March 30, 2004 8:32 PM
Subject: QUESTION: Homebrew Spread spectrum


How to synchronize to direct-sequence spread
spectrum should be obvious (think Costas Loop).

A sliding-window correlator is a common approach,
otherwise. Three correlators in parallel. One runs
a little ahead, one is on time, the third runs a
little behind.

The LO free-runs (deliberately) a little slow or
fast. When the locally-generated PN sequence lines
up with the received sequence, the outputs from the
early/late correlators track the LO, while the
on-time correlator provides the output.



Thanks for the info, Laura. I never did any work with a Direct sequence
system, but this makes a lot of sense.


Jim Pennell
N6BIU

----- Original Message -----
From: "Laura Halliday"
Newsgroups: rec.radio.amateur.homebrew
Sent: Tuesday, March 30, 2004 8:32 PM
Subject: QUESTION: Homebrew Spread spectrum


How to synchronize to direct-sequence spread
spectrum should be obvious (think Costas Loop).

A sliding-window correlator is a common approach,
otherwise. Three correlators in parallel. One runs
a little ahead, one is on time, the third runs a
little behind.

The LO free-runs (deliberately) a little slow or
fast. When the locally-generated PN sequence lines
up with the received sequence, the outputs from the
early/late correlators track the LO, while the
on-time correlator provides the output.



Thanks for the info, Laura. I never did any work with a Direct sequence
system, but this makes a lot of sense.


Jim Pennell
N6BIU