Introduction to the Ham Hopper-1
In our last issue we presented the first article on the Ham Hopper-1 (see page 13 of March 1994 SSS).
That short article only gave the highlights of this project. In this introduction we will
give some background information, a preliminary specification for the Ham Hopper-1 and block
diagrams for both the transmitter and receiver sections. Future articles in this series will
provide complete construction, operation and software/ protocol development information.
Ham radio SS experimentation started in the early 1980's.
Several hams received STAs (Special `Temporary Authority) from the FCC to try
various SS experiments. These early tests and other amateur radio SS developments
are well covered in the ARRL Spread Spectrum Sourcebook . By 1983 the FCC revised
Part 97 rules to permit a narrowly defined set of SS operating standards for
amateur radio. Needless to say, SS never caught on in the world of ham radio.
Many people say that the rules have been too restrictive (only 3 legal codes --
eliminating the possibility of CDMA, for instance). Others think that the
popularity of packet stole the limelight form ham SS operations. I believe that
SS never got popular just because it is (and has been) so specialized and honestly
rather complicated for the average ham.
So now it is half way through 1994 and the ARRL board of directors has finally
decided that SS may somehow help ham radio. I hope they go ahead with the
request for rule making to the FCC, because it gives us a chance to help
launch ham radio operations in the US. Remember TAPR? Well, if an
organization like TAPR were to get behind SS, put out a kit, make public
domain software available -- it might just fly, right?
Well that's exactly what ARSS (Amateur Radio Spread Spectrum) is trying to do.
ARSS is a non-profit San Francisco bay area group of hams that are in the
process of pulling the Ham Hopper-1 project together. The members of ARSS
are all volunteer hams with interest in hardware, software or just operating.
They are donating their time (and money) in an effort to help popularize SS.
So if you are interested in SS, like to build things or just want to see
what this project is all about -- follow this series of articles. This
project is primarily aimed at the ham radio market with hams building up
the kits that will be offered. However, if you are an educator, avid
tinkerer or just curious, you are welcomed to build a Ham Hopper-1 and
use it in the classroom or in your lab. Just remember that the 50 to 54 MHZ
spectrum requires a ham license to radiate any energy . Without the license,
you must use dummy loads or coax cable connections between units (or frequency
convert to some unlicensed ISM band. like 902-928 Mhz).
The major objective for the Ham Hopper-1 project is to make the equipment
simple to build, test and operate -- commensurate with the lowest cost
possible design (goal: less than $200 for the kit).
Some compromises are obviously necessary to meet these objectives.
A second order objective is to provide digital communications capability at
least 10 to 20 times the speed of current ham packet operations and provide
a vehicle for developing and testing various digital voice packetized
techniques. To meet all these objectives nearly simultaneously requires
some thought and will probably cause some iterations in the design as
it evolves. First off, it was decided that the Ham Hopper-1 will be the
first and simplest version of this design that serves as a "starter
kit" for ham SS operations. Second, later versions of the Ham Hopper
series will add some "bells and whistles" but will still be
downwardly compatible with prior versions. Thus we will add a DSP IC to
the second generation Ham Hopper. This second version will undoubtably
possess the capability of Direct Sequence (DS) and Hybrid (combined DS
and frequency hop. FH, modulation). The third version of the Ham Hopper
will probably include digital voice vocoding and time division duplex
(TDD) operation for packetized digital voice.
It is the intent of his ARSS project to design the basic Ham Hopper-1
so that "daughter boards" or plug-in modules can be added later
to accommodate the later enhancements. So even if you build the Ham
Hopper-1, it can still be easily upgraded to any configuration that evolves.
We also intend to provide modular and expandable software / firmware for
this project and open protocols. This software / protocol approach is meant
to encourage those of the ham community who are more interested in the software
side of things to work away and contribute to the evolution of Ham SS technology.
To encourage this software development we plan to make available a software /
protocol developers kit at a very nominal cost.
Finally, one of our major objectives is to make the Ham Hopper-1 hardware widely
and inexpensively available to the ham community. To accomplish this end we intend
to make this design available to several manufacturers on a license or royalty basis.
These manufactures may make available complete, assembled and tested versions of the
Ham Hopper-1 for various amateur bands. We intend to commercialize this product, as
well, at 915 Mhz, 2.4 Ghz and perhaps 5.7 Ghz.
Any manufacturer who licenses the Ham Hopper-1 design will receive complete source
code as well engineering support from ARSS to build a viable commercially
marketable product for their needs. Interested companies should contact
ARSS through SSS or RF/DD for more information. The license fees and/ or
royalties planned are very nominal and are needed to defray the out of pocket
costs that ARSS expects to incur in completing the development of this project.
All information about the hardware, software and firmware or protocols used
in the Ham Hopper-1 are released to the public domain only for the non -
commercial use of individuals who will build, test, improve or in some
way contribute to the advancement of the ham radio state of the art in SS.
Any other use of the information contained in this series of articles on
the Ham Hopper-1 is strictly prohibited and ARSS will take any and all
measures available at law to enforce its rights. This limited public
release of the Ham Hopper-1 design means that anyone can build a single
copy of the unit(s) for their own personal or educational use -- however,
a school , university, company or radio club project that builds more
than one unit of the Ham Hopper is infringing on ARSS's data rights. In
most cases, ARSS will specifically provide royalty-free licenses to ham
radio clubs or legitimate college / university projects that want to use
this design. But please contact ARSS before starting to build more than one
Ham Hopper-1 unit -- OK? Any commercial use of the Ham Hopper-1 design
including improvements, derivatives, modifications or "slight"
changes to the basic design will require a license and the payment of
appropriate fees and royalties.
If you have followed us so far, you probably want to know more about the
Ham Hopper-1 Preliminary specifications for the Ham Hopper-1 transceiver
are highlighted in the table on page 11. The block diagram of the
transmitter section is presented on page 11, while the receiver block
diagram is shown on page 12.
Bear in mind that these specs are subject to some change as the design
evolves, but our goals for the performance of this unit are clarified
in these preliminary specs. ARSS is open to comments and suggestions
for a short amount of time. If you would like to see some changes or
additions / corrections to the spec goals -- please write or FAX us
We're running out of space again, so just a few comments about the
block diagrams. This design uses a DDS that is common to both the
transmitter and receiver. On transmit, the DDS provides the frequency
hopping of the output signal -- GMSK modulation is applied to the PLL's
VCO. Inreceive, the DDS is mixed up to provide the frequency hopping
local oscillator The transmitter may seem unconventional, but it's
simple and straightforward. The receiver is a single conversion
superheterodyne with a single IF of 10.7 Mhz (where nice, cheap
ceramic bandpass filters are readily available). More on the block
diagrams and some initial schematics, next issue.
Much More to Come
We will lay out this entire project in succeeding issues of SSS. In
the meantime, consider what this project might do for ham radio. ARSS
hopes that the Ham Hopper-1 can bring Ham radio out of the technology
"Dark Ages" and bring back some experimental interest in today's
hams. If this project succeeds and it will if you support it -- we may
be ready for 21st century technology! Catch you hopping!
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