Randy Roberts, the founder of Spread Spectrum Scene Online, was an avid
ham radio operator. Listed below is his proposal for a spread spectrum radio for ham
use. The information is a bit dated, but can still be of interest for someone who wants
to do some tinkering....
We want to encourage experimentation with SS techniques! When SSS was
a paper publication, we published a number of "how to" articles, one or two
variants on the theme of a DS STA radio (for Buass' STA), two gener-
ations of "Ham Hopper" transceiver designs and a number of other tidbits
for the avid or budding experimenter. Here's our first update:
Here's my proposal:
I (and RF/SS) will grant a THREE YEAR NON-EXCLUSIVE LICENSE
to TAPR [or any other Bona Fide Amateur Radio Organization], at
NO COST WHATSOEVER, which includes a relatively complete
design and documentation package for a "Universal," DSSS / FHSS
/ Hybrid FH-DS radio-modem with the following initial design
characteristics and specifications preliminarily outlined below.
This licensed design package will allow the user to rapidly assemble
the pieces needed to offer either kits or completed products to the
Amateur Radio Community. These kits can be modular in capability
and can be designed with expansion in mind. The performance of this
licensed design is State of the Art in every way. It uses the latest in
ASIC technology and provides better than commercial WLAN SS
communications that rival what the US military are using today!
The radio-modem is used ONLY for Amateur / non-commercial or
to-be-negotiated educational uses.
TAPR (or any other Bona Fide Amateur Radio Organization) and
other assorted / interested volunteers supply labor and materials,
as needed, to fully develop and test this new design.
TAPR (or any other Bona Fide Amateur Radio Organization) sets
up a Project / Team organization to provide direction, guidance and
start on a "Ham Radio SS" Standard, ASAP!
The draft standard mentioned in (3) above is ready for circulation
and comment by 1 May, 1997 AND that the Final Interium Standard
for Ham SS operations is released by 1 August, 1997.
*** HOT from the LAB -- ACTUAL Spectrum Plots from our HP8561A ***
Spectrum Analyzer on the RF/SS Breadboard SST-1 Radio-Modem
The plot on the left is without any power amplifier on the radio-
modem's output. The righthand plot is with a linear 100 mW
power amplifier. Both plots use a master XTAL Osc. of 5.12
MHz for a PN Chip rate of 1.28 MHz (see first spectral nulls
at +/- 1.28 MHz from the suppressed carrier). Data rate for
both plots is 20.3 kbps -- for a processing gain of 63 chips per
bit or 18 dB. NO DATA is being transmitted in either plot!
*** Here's another View: ***
The lefthand plot shows the radio-modem's actual occupied RF
Bandwidth -- BW(-20 dB) -- or 99% BW = 1.8 MHz (this is
only 1.41 x Chip Rate!) The markers are a "little" hard to see --
aren't they? The righthand plot shows the details of the
spectral lines within the DSSS signal. The lines are 20.3 kHz
apart (= the Data Rate). Note also that the (suppressed )
carrier is 20.67 dB down from any line! Both plots uses an X.O.
of 5.12 MHz for a PN Chip rate of 1.28 MHz and ALL plots
here use BPSK-DSSS modulation. NO DATA is being trans-
mitted in either plot!
*** Want to go FASTER?: ***
*** How about larger plots?: ***
This plot uses an X.O. equal to the carrier frequency =
29.000 MHz for a PN Chip rate of 7.25 MHz and a Data Rate
of 120 kbps. NO DATA is being transmitted in this plot!
*** How about SLOWER?: ***
This plot uses an "audio" clock = 7560 Hz for a Chip rate of
1890 Hz and a Data Rate of 30 bps (that is 30 Baud!) This
might work for EME -- anyone want to try it? NO DATA is
being transmitted in this plot either!
*** How About another Band?: ***
*** How about Frequency Hop?: ***
We will be posting this kind of info plus more test results,
schematics and lots of other stuff on this proposed design,
if there is any interest -- email us if you want more info!