[Linux-ham] 802.11 to Part 97 ...

sjackson at radarfind.com sjackson at radarfind.com
Wed Mar 9 14:37:32 EST 2005

Tanner, Kevin:

The ARRL "hinternet" effort isn't what I'd call a concerted effort.  It's
more like a "set of loose guidelines" . and frankly, not very useful in
scope.  Notice it's gone exactly nowhere ... As an ARRL Life Member, I can
say that!  ;-)

In the grander sense of things, what I'd call a "concerted effort" is more
like what's done with regional repeater systems; examples around here are
Graham Repeater Assn. (WA1YYN) and Piedmont Coastal Repeater Network
(K4ITL).  Tight control, system specs adhered to, one source for hardware.

You can indeed 'hack' into some OLDER 802.11 access-point products and take
control over the RF decks.  (Newer gear has all the innards hidden in
silicon and not addressable externally.)  With appropriate documentation and
an add-on microcontroller (PIC 16F series does nicely), you could re-purpose
about any throwaway 802.11 CCK stuff, for Part 97 use.  

I don't see any good way to hack into any PCMCIA cards of the last 5 years
or so because they all have their control interface abstracted to the degree
that it would be nearly impossible (if not impossible) to get the level of
control you need.  Maybe the pre-802.11 cards, but, you'd have to
reverse-engineer them from the driver level, big P.I.T.A.

So, you'd essentially be adapting access points into being ham-band base
stations.  Once done, ANY media now is OK! Including audio ... Because it's
digital.  This is key to being useful and innovative.

Once you did the radio mods and built a control plane, you could build a
hybrid MMIC-based amplifier to boost the 275 mW to a useful power level,
say, 2 W (~8 dB fwd gain) and maybe the same in the reverse, and sync a
hot-carrier diode switch to the new CCK-OOK protocol you'd have to create.
For Layer 2, ATM would be handy (that's why Icom uses it) or simply re-use
AX.25 or even V1 Ethernet.  Since these are well-known, it's all FCC legal
as long as you ID and don't carry commercial traffic.  

A comms protocol above it, such as THEnet or ROSE from the old packet days,
would add lots of flexibility.  Tom W2VY wrote much of this code and he's
still around.  (Tell him I sid hello!)

Afterwards, with some nice hardline type coax (line losses at 2.4GHz are
nasty) such as Andrew FSJ4-50, you could feed a Wilkinson microstrip power
divider (esy to make) and a series of horns, each pointed at the other
stations which would be configured identically.  With a net +30 dBm launch
power into a 20 dB gain antenna, you'd have 100W ERP at 2.4 GHz ... 100W ERP
is enough to get some decent range within a Fresnel zone, despite the gear
operating literally at the worst possible frequency.  

Assuming *optical* line-of-sight, and no more than 30% relative humidity,
you could go as far as 100 miles!  But realistically speaking, range would
be more on the order of 1 mile or so in most places around here.

To make a network, you'd have to have hams spaced at roughly these
distances, with substantially identical stations.  To do this, you could
build up several stations and distribute them to local hams in range.
Perhaps you could offset the high cost by sharing the burden in some way,
maybe by adding network-accessed features such as a weather station, which
others might want.  

Make sure you create a frequency matrix that substantially avoids the 802.11
channels.  No need to have irate WiFi-equipped neighbors at your door!  

Also, keep the 100W free-space microwave ovens (basically what you're
creating) from pointing at people or buildings.  Safety first.

I'm not trying to dissuade either of you at all; in fact, quite the
opposite.  It's how I learned most of what I know, having done *lots* of
this kind of thing over the last 26 years.  This could be a great learning
experience because it brings together many disparate skill sets -- some of
which Tanner already has, judging by his on-line resume.  


Steve KZ1X/4

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Stephen S. Jackson
RadarFind Corporation
2 Davis Drive
Research Triangle Park, NC  27709-3356
sjackson at radarfind.com

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