----- 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

(Timothy C Holtom) wrote in message . com...
Can anyone out there tell me a good source of practical information
(schematics and the like) for building SS transmitters and receivers.
I'm particularly interested in how I'd design the part of the receiver
that acquires then tracks the synchronisation signal from the
transmitter (correlation etc)

I did an initial scout around on the net but the only stuff I could
come up with was TAPR but there's seemed to have been cancelled.

I'm into experimenting, and not afraid of math (an electronic engineer
from a long time ago...)


Can anyone help me here...


Tim

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?

Cheers,
Tom

Timothy C Holtom wrote:

Can anyone out there tell me a good source of practical information
(schematics and the like) for building SS transmitters and receivers.
I'm particularly interested in how I'd design the part of the receiver
that acquires then tracks the synchronisation signal from the
transmitter (correlation etc)

I did an initial scout around on the net but the only stuff I could
come up with was TAPR but there's seemed to have been cancelled.

I'm into experimenting, and not afraid of math (an electronic engineer
from a long time ago...)


Can anyone help me here...


Tim

The '88 ARRL handbook had a spread-spectrum project. You'll need to
find a buddy to implement one, too.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

(Timothy C Holtom) wrote in message . com...
Can anyone out there tell me a good source of practical information
(schematics and the like) for building SS transmitters and receivers.
I'm particularly interested in how I'd design the part of the receiver
that acquires then tracks the synchronisation signal from the
transmitter (correlation etc)

I did an initial scout around on the net but the only stuff I could
come up with was TAPR but there's seemed to have been cancelled.

I'm into experimenting, and not afraid of math (an electronic engineer
from a long time ago...)


Can anyone help me here...


Tim

Hi Tim,
this wont be the answer you want but the usual method is to horribly
overdrive your ssb transmitter/linear and that way you are all over
the band! (a joke, OK?)

Miss Smarty Pants (aka Laura Halliday) in her usual inimatble(sp)
style has answered as well, I dont have a PHD so havent a clue what
she is talking about. But she says it should be obvious, maybe you can
figure it out and tell the rest of us uneducated slobs...

73 de VK3BFA Andrew

(Andrew VK3BFA) wrote in message . com...

Hi Tim,
this wont be the answer you want but the usual method is to horribly
overdrive your ssb transmitter/linear and that way you are all over
the band! (a joke, OK?)

Miss Smarty Pants (aka Laura Halliday) in her usual inimatble(sp)
style has answered as well, I dont have a PHD so havent a clue what
she is talking about. But she says it should be obvious, maybe you can
figure it out and tell the rest of us uneducated slobs...

What's with the personal abuse? Her answer made perfect
sense to me.

A direct sequence signal is spread by BPSK modulation at the
chip rate. Double the frequency and the 0/180 phase shifts
become 0/360, removing the spreading.

- Jack

(Jack Gibson) wrote in message . com...
(Andrew VK3BFA) wrote in message . com...

Hi Tim,
this wont be the answer you want but the usual method is to horribly
overdrive your ssb transmitter/linear and that way you are all over
the band! (a joke, OK?)

Miss Smarty Pants (aka Laura Halliday) in her usual inimatble(sp)
style has answered as well, I dont have a PHD so havent a clue what
she is talking about. But she says it should be obvious, maybe you can
figure it out and tell the rest of us uneducated slobs...

What's with the personal abuse? Her answer made perfect
sense to me.

A direct sequence signal is spread by BPSK modulation at the
chip rate. Double the frequency and the 0/180 phase shifts
become 0/360, removing the spreading.

- Jack

Hi Jack,
it wasnt meant as abuse - merely that I didnt understand Lauras
references. If you think being called a smarty pants is abuse, then
you have had a VERY sheltered life - or perhaps its cultural, - BTW -
I went to her site and read the papers she has there - the writing is
clear, succinct and on a level that I can understand. Maybe it was
asking a bit much for Laura to "dumb down" her reply, and I have no
right to expect her to do this. But I rely on these groups as
tutorials on the wide variety of things I dont understand - I am a
mere technician who spends his working life trying to figure out what
the design engineer was trying to do and why it failed after only a
few months in service.

Hope this clears this up

de VK3BFA Andrew

(Jack Gibson) wrote in message . com...
(Andrew VK3BFA) wrote in message . com...

Hi Tim,
this wont be the answer you want but the usual method is to horribly
overdrive your ssb transmitter/linear and that way you are all over
the band! (a joke, OK?)

Miss Smarty Pants (aka Laura Halliday) in her usual inimatble(sp)
style has answered as well, I dont have a PHD so havent a clue what
she is talking about. But she says it should be obvious, maybe you can
figure it out and tell the rest of us uneducated slobs...

What's with the personal abuse? Her answer made perfect
sense to me.

A direct sequence signal is spread by BPSK modulation at the
chip rate. Double the frequency and the 0/180 phase shifts
become 0/360, removing the spreading.

- Jack

Hi Jack,
it wasnt meant as abuse - merely that I didnt understand Lauras
references. If you think being called a smarty pants is abuse, then
you have had a VERY sheltered life - or perhaps its cultural, - BTW -
I went to her site and read the papers she has there - the writing is
clear, succinct and on a level that I can understand. Maybe it was
asking a bit much for Laura to "dumb down" her reply, and I have no
right to expect her to do this. But I rely on these groups as
tutorials on the wide variety of things I dont understand - I am a
mere technician who spends his working life trying to figure out what
the design engineer was trying to do and why it failed after only a
few months in service.

Hope this clears this up

de VK3BFA Andrew

(Andrew VK3BFA) wrote in message . com...

Hi Tim,
this wont be the answer you want but the usual method is to horribly
overdrive your ssb transmitter/linear and that way you are all over
the band! (a joke, OK?)

Miss Smarty Pants (aka Laura Halliday) in her usual inimatble(sp)
style has answered as well, I dont have a PHD so havent a clue what
she is talking about. But she says it should be obvious, maybe you can
figure it out and tell the rest of us uneducated slobs...

What's with the personal abuse? Her answer made perfect
sense to me.

A direct sequence signal is spread by BPSK modulation at the
chip rate. Double the frequency and the 0/180 phase shifts
become 0/360, removing the spreading.

- Jack

(Timothy C Holtom) wrote in message . com...
Can anyone out there tell me a good source of practical information
(schematics and the like) for building SS transmitters and receivers.
I'm particularly interested in how I'd design the part of the receiver
that acquires then tracks the synchronisation signal from the
transmitter (correlation etc)

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

A sliding-window correlator is a common approach, other-
wise. 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.

Look in back issues of Wireless World from 1993 for a
fully worked-out example.

Laura Halliday VE7LDH "Que les nuages soient notre
Grid: CN89mg pied a terre..."
ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte