Experimrnting with spread spectrum
 

greets all,

Am looking to start experimenting with spread spectrum communications.

I'm pretty much starting from scratch in this area. Could anyone please point me to a
good starting point? Thanks.

Dave

Am looking to start experimenting with spread spectrum communications.

I'm pretty much starting from scratch in this area. Could anyone please
point me to a
good starting point? Thanks.


The ARRL published a book about spread spectrum quite a while ago. The
Brittish magazine "Electronics & Wireless World" published a 2 part article
at least 5 years ago.

Wim

Web sites for Spread Spectrum mode

http://www.tapr.org/tapr/html/Ffhsspaper.97.html

http://www.tapr.org/ss/

http://sss-mag.com/index.html

--
Caveat Lector

Am looking to start experimenting with spread spectrum communications.

I'm pretty much starting from scratch in this area. Could anyone please
point me to a
good starting point? Thanks.

On Sun, 09 Jan 2005 18:51:50 -0800, Bill Turner wrote:

Spread Spectrum = Legalized Jamming.

Please don't.

Hi bill, I plan on experimenting with this on a very small scale (as far as power
output goes) and would be monitoring the power density of the spectrum matrix at all
times. It's just something I've always been very interested in.

Dave

On Sun, 09 Jan 2005 09:46:20 GMT, "Wim Ton" wrote:

The ARRL published a book about spread spectrum quite a while ago. The
Brittish magazine "Electronics & Wireless World" published a 2 part article
at least 5 years ago.

Wim

Literally the last book I read that had anything to do with spread spectrum was the
1993 edition of the ARRL Handbook. I read enough of the basic theory to get me very
interested, and it's been stewing in the back of my mind ever since. Recently I saw
something the refired my interest once again in spread spectrum.

A Quote:

"Also, a 500mw spread spectrum device can easily have an effective range of over 20
miles. In 1994 I field tested a spread spectrum LPD/LPI handheld radio designed for
downed pilots. The power would vary between one half milliwatt to one full watt based
on the quality of a duplex link. With power levels below 25mw we could communicate
clearly at a distance of 45 miles on the open ocean (from a life raft), and 15 miles
in the dense woods of Maine. When the device was tested in a dense urban area, a
range of 2500 to 8600 feet was obtained while keeping the power output *below* 15mw."


I've seen two publications on the web regarding spread spectrum:

The ARRL spread spectrum sourcebook at:
http://www.powells.com/cgi-bin/biblio?isbn=0872593177

and

TAPR's Spread Spectrum Update at:
http://www.tapr.org/tapr/html/Fpub.ss.html

Has anyone read either of these publications? I'm afraid I'm just a little rusty on
the old algebra, trig and calculus. So a relatively math-free (not completely
math-free, mind you) book would be appreciated.

As I understand it, the ARRL spread spectrum sourcebook is evidently a collection or
articles put out by the ARRL/AMRAD on spread spectrum experiments. Would this be
correct?

Like I said, I'm a beginner in this area, but usually learn quickly. Is there any
such thing as, perhaps, a few "ready-made" kits or consumer devices that could be
immediately utilized in exploring this fascinating field? This would be very nice
indeed.

Dave

Thanks for the info, Caveat. Looks like I may have had run across one of your links
in all my searching :)

There are many question I have regarding SS, but one that's bothering me in
particular. Regarding the PN spreading sequence, these sequences obviously have to be
aligned perfectly in both transmitter and receiver. Naturally they could be kept in
sync if both circuits were initialized at the same time.

However, 3 things: 1) The circuits will not be initialized at the same time in 99% of
most cases, as in the use of, say, a portable field radio. 2) If they were
synchronized at the same time, well, no clock or oscillator is perfect. It would
eventually drift. 3) As I understand it, there is no initial "handshake" signal at
the beginning of transmission with the receiver to initialize/syncronize the PN
sequences on both ends.

So in short, how do the PN sequences became and remain synchronized through time?
Thanks.

Dave


On Sun, 9 Jan 2005 07:02:01 -0800, "Caveat Lector" wrote:

Web sites for Spread Spectrum mode

http://www.tapr.org/tapr/html/Ffhsspaper.97.html

http://www.tapr.org/ss/

http://sss-mag.com/index.html

--
Caveat Lector

Am looking to start experimenting with spread spectrum communications.

I'm pretty much starting from scratch in this area. Could anyone please
point me to a
good starting point? Thanks.

David H. wrote:
Thanks for the info, Caveat. Looks like I may have had run across one of your links
in all my searching :)

There are many question I have regarding SS, but one that's bothering me in
particular. Regarding the PN spreading sequence, these sequences obviously have to be
aligned perfectly in both transmitter and receiver. Naturally they could be kept in
sync if both circuits were initialized at the same time.

However, 3 things: 1) The circuits will not be initialized at the same time in 99% of
most cases, as in the use of, say, a portable field radio. 2) If they were
synchronized at the same time, well, no clock or oscillator is perfect. It would
eventually drift. 3) As I understand it, there is no initial "handshake" signal at
the beginning of transmission with the receiver to initialize/syncronize the PN
sequences on both ends.

So in short, how do the PN sequences became and remain synchronized through time?
Thanks.

Two ways that come to mind immediately:

1) The transmitter sending its state periodically, so that the
receiver can jam that into its spreading or hop control
registers and be instantly synchronized. No good for *secure*
comms, but great for insecure comms.

2) The transmitter using spreading or hop control based in some
way on (GPS) time, say by automatically loading new control
state periodically. The receiver would load the same control
state for that time period, and then could slew the clock
forward in time until it detected synchronization. This is a
variation on (1) which *is* good for secure comms.

Drift can be corrected by circuitry in the receiver, from the received
signal. If the link is via satellite, drift (and Doppler shift) *must*
be corrected in the receiver to maintain sync.

--
Mike Andrews

Tired old sysadmin

AIUI, the receiver does a number of correlations against
the incoming signal to establish synchronisation.

"David H." wrote in message
...
So in short, how do the PN sequences became and remain synchronized
through time?
Thanks.

The ARRL spread spectrum sourcebook at:
http://www.powells.com/cgi-bin/biblio?isbn=0872593177

and

TAPR's Spread Spectrum Update at:
http://www.tapr.org/tapr/html/Fpub.ss.html

Has anyone read either of these publications? I'm afraid I'm just a
little rusty on
the old algebra, trig and calculus. So a relatively math-free (not
completely
math-free, mind you) book would be appreciated.

As I understand it, the ARRL spread spectrum sourcebook is evidently a
collection or
articles put out by the ARRL/AMRAD on spread spectrum experiments. Would
this be
correct?

I had the ARRL spread spectrum sourcebook (before I sold it on eBay). It is
a bit a jumble of chapters:
A lot of legal and restrictive stuff (as SS originated in military comms and
can be used for covert and/or jam resistant communication)
Several articles on shift register sequences and coding gain.
Synchronisation
Some designs, but the digital parts are quite obsolete now.

Wim

So in short, how do the PN sequences became and remain synchronized
through time?
Thanks.

The E&WW article used a Delay Locked Loop, 3 decoders, one fed with the
actual PN secquenc, one with a leading version and one with a lagging
version. The error signal was used to correct the PN clock.

What some military radios use is that the receiver hops much slower than the
transmitter before achieving synchronisation, so I will catch a signal at
some time.

Wim