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Notes from the Bikelab

Issue #10 -- 5/28/91

by Steven K. Roberts

Copyright (C) 2000 by Steven K. Roberts. All Rights Reserved.


The Antenna Farm
Nifty Regulators

"Daddy toys!"

-- concise assessment by Julia Selfridge, age 2,
upon being introduced to BEHEMOTH for the first time.

Well, there are now 49 days to departure, and I'm in the D
phase of the PFD phenomenon that most concisely describes my
work habits (Procrastination Followed by Despair). It is clear
now that the machine will indeed roll. It has gears, brakes,
lights, a Cateye, and a radio... all working. There's pack
space, and most areas are waterproofed. Many subsystems are
nailed down on the bike and have been tested on umbilici, but
now await cabling or software to become useful. The primary
task is to complete as many "lab" tasks as possible in the next
7 weeks... for after that, I will no longer have the milling
machine, hardware inventory, high-speed scope, huge work area,
or all those wonderful new daddy-toys still shrink-wrapped on
the bench.

Good thing this is a passion, eh?

Actually, the project is moving faster than ever -- I have new
help. Answering my recent call, Martin Rowland has moved up
from San Diego to be the techno-gofer and general assistant
between here and departure. This helps a lot, greatly reducing
the time spent moving my body around Silly Valley in order to
acquire objects. David K. Z. Harris of Telebit is donating
some time to bring up the ham gear and related components, Bill
Muench and Mike Perry are helping get the FORTH code started,
Steve desJardins is building the pneumatically actuated landing
gear, Bob Lockhart is doing the PCB CAD work on the audio
crosspoint network, and the various people I've credited before
are still helping with various projects... collectively making
it likely that BEHEMOTH will indeed raise a quizzical eyelid
and utter "hello, world" just in time for RAGBRAI.

Incidentally, if you've been reading this alias for a while and
still harbor a quite reasonable suspicion that it's all twisted
technoid fiction, there will be some current photos in the
media during the next couple of months. Sometimes editorial
schedules slip, but I've been told of the following:

* 5 page spread in the July DISCOVER, with detailed captions
* 3 pager in the August BICYCLING, including stunning photos
* interview with pix in the next MONDO 2000
* article in the 5/28 SF EXAMINER, and CHRONICLE later this week
* a reprint in the next issue of ComputorEdge from San Diego
* technical article with photos in NOMADNESS #10

Or come to Iowa during the last week in July and join 10,000
cyclists in a mad, drunken 430-mile ride from Missouri Valley
to Bellevue...

On with the technical news!

The Antenna Farm

BEHEMOTH is bristling with a veritable thicket of skyhooks,
some of which have already received mention in this series.
Now that they're all mounted, however, it's a good time for a

Technically speaking, the bike carries 18 separate antennae,
not including all the unintended ones (cables, LCD panels,
spokes, and probably my nose). This all makes me wish for some
magical phased array that could do it all... for every one of
these has to be packaged, cabled, waterproofed, positioned
optimally relative to the others, dragged through the viscous
medium known as air, and hauled up hills. But, boy, can I ever

Let's cruise up the electromegnatic spectrum from 150 kHz to 14
GHz and look at all the bike parts that radiate, resonate,
ionize the atmosphere, or pluck whispers from the ether...

Active SWL whip (150 kHz - 30 MHz and 78-108 MHz)

This is seldom deployed while riding, but is the 46" amplified
whip that came with Sony's new ICF-SW1 miniature digital
shortwave receiver. Clever box -- the radio has its own local
whip, or you can plug in an RF amplifier module connected by
micro-coax on a little reel to the big one.

HF mobile dipole (3-28 MHz)

Featured in issue #1 of this series, this is proving to be a
dramatic alternative to the traditional mobile vertical for HF
ham operation (I use an Icom 725 transceiver). The basic
problem with HF verticals is that they use the vehicle as a
counterpoise -- the bike is not only too small (hah) for
effective use on low frequencies, but there is a very real
danger of RF hot spots in this mode. The solution is a
balanced antenna such as a dipole, and this one is constructed
of two Outbacker Jr 7-band verticals (75-40-20-17-15-12-10
meters). They are normally stowed against the telescoping
fiberglass mast (BYP, or Big Yellow Pole) on the back of the
trailer, but can be flipped up to either a horizontal or
vertical dipole configuration (also V or inverted-V, actually,
though I haven't tried it) and locked with knobs. The entire
assembly while mobile is about 7 feet off the ground, extending
to 13 feet when I'm camped. The BYP is hinged, and has a
breakaway mechanism designed by Steve desJardins to protect the
trailer body if I do something stupid like ride under a low
tree limb.

HF wire dipole pack (7-28 MHz)

Experience has shown that there's no substitute for full-size
wire dipoles, so there's a little nylon bag stuffed in the
satellite basement under the WASU subflooring. Inside is a 50'
hank of RG-58 coax, some nylon rope, and simple dipoles for
40/15, 20, and 10 meters, each with an SO-239 connector at the
center insulator. I'll carry this until I have a chance to A-B
it against the Outbackers under a variety of conditions, and
will toss it with pleasure if the difference turns out to be
minor. Stringing dipoles between trees can be an amusing
ritual, but it does get old after a while -- and is seldom
worth the bother for a short layover. (Actually, I just made a
tough decision yesterday to remove the MFJ tuner and artificial
ground currently built into the communications bay. The plan
was to carry a military surplus longwire and load it up
whenever I'm stopped, but it's just too much of a pain. I've
never been happy with anything requiring a tuner, and the
danger of high RF voltages from pilot error with grounding is
too great. Besides, I need the commbay real estate.)

Pager/CB helical duck (27 MHz)

There are three whip antennas on the trailer, evenly spaced
along the centerline of the solar panels. Their mounting
platforms are electronically bonded to the aluminum substrates
of the panels, making them an excellent ground plane. (Someone
pointed out that the giant semicrystalline silicon rectifiers
atop this ground plane may detect transmitted RF and impose
noise on the battery bus -- any RF wizards out there want to
comment on this?) The most forward of these antennas is the CB
helical duck from Larsen, and it is switched through a couple
of BNCs in the coax patch panel between the default security
pager and the culturally useless but occasionally handy CB
rig in the trailer.

2-meter halfwave (144-148 MHz)

The classic workhorse antenna for bicycle-mobile 2-meter
operation is the Larsen halfwave whip. I've used this for
years with excellent results: it has a wide radiation angle
and accepts a seat-back mounting 15 degrees off vertical
without loss of gain fore-aft; it needs no ground plane; it's
thin and discreet. If you operate bicycle mobile, forget the
1/4 and 5/8 wave units and get one of these. (A J-pole is a
higher-gain option, but is generally much more delicate.) This
unit, on an NMO mount bolted to a plug TIG-welded into the seat
back, is kept from flailing uncontrollably by a sliding
coupling to the fiberglass flagpole plugged into the seat
tube. A coax cable runs directly to the console 2-meter rig --
a hacked Icom u2AT, repackaged and powered via a 9-volt Power
Trends switcher. Although there is a dual-bander on the
trailer, using it along with the requisite coax patch panel,
duplexer, and disconnect headers would require 6 coax connector
pairs... a bit excessive for a micropower transceiver!

(2) wireless intercom helical whips (169-186 MHz)

One of the interesting features of BEHEMOTH's security system
is the ability to open a bidirectional audio link between bike
and manpack, letting me find out when the beeper sounds if the
situation justifies further action (often, a level-2 violation
is just someone harmlessly touching the machine out of
curiosity). I once tried this via 2 meters, but the very first
test under real conditions yielded some brain-dead bozo
muttering: "what the **** is this piece of ****?" I panicked,
imagining the reaction of the FCC and the amateur radio
community, and immediately disconnected the circuit. This
time, it's a license-free low-power wireless intercom good for
a few hundred feet, and the antennas, again from Larsen, are
custom helical rubber ducks -- one on the RUMP and the other on
the manpack.

VHF-UHF dual-bander with duplexer (144-148 and 440-450 MHz)

This Larsen whip (guess you're starting to notice that I like
Larsen antennas -- you can get more info on them by calling the
company at 800-426-1656) is a shunt-fed grounded coil
dual-bander, which is 5/8-wave at 2 meters and 1/2 over 1/2
colinear at 440. Nice unit. It holds the coveted center spot
on the solar ground plane, and is cabled to Larsen's AD 2/70
duplexer. This presents two spigots, one for each band, and
these are normally cabled to the Yaesu 290 and 790 multimode
transceivers (my big guns for VHF and UHF). In case I haven't
mentioned them earlier in this series, these are excellent
radios: very low battery drain, FM-CW-USB-LSB modes, plug-on
modules for 25-watt amplifiers or battery packs, and pleasant
user interface. I have used the pair, aided by a pair of ARR
preamps and a KLM satellite antenna, to work OSCAR 13 with good
results, and on the bike they will be used for the microsats,
packet, and long-range terrestrial operation. Incidentally,
this antenna tends to flail around if unsupported -- I made a
guying collar that slips over the top element onto the center
coil, and attached four thin guy lines down to the solar

VHF-UHF dual-band helical whip (144-148 and 440-450 MHz)

Though not mounted on the bike itself, this one counts in our
antenna chautauqua -- it's the rubber duckie attached to the
Icom IC-24 dual-band handheld transceiver. Amazing device.
Word on the street is that the antenna that comes with the Icom
is not so hot, but I think they changed it in more recent
deliveries. I have both the original Icom and a Larsen of
similar dimensions, and will experiment with the 15" Diamond
dual-bander before packing up for departure.

(2) UHF packet link helical whips (457.525 and 457.575 MHz)

The bike-to-manpack data link consists of a pair of Motorola
Radius RNET transceivers, and Larsen quarter-wave UHF ducks cut
to my licensed itinerant and cargo frequencies are mounted on
the RUMP at shoulder level and on a flip-up coax elbow on the
Zero manpack. The coax patch panel in the trailer and a Lemo
waterproof connector on the RUMP allow the bike's data radio to
be patched to the much more efficient dual-bander for
long-range use.

VHF-UHF television whip (55-211 MHz and 471-801 MHz)

This is just the whip antenna on the Sony Watchman TV set.

UNGO security remote (300 MHz)

Inside the RUMP, the UNGO box security system is mounted on the
forward fiberglass wall -- watching for movement via a blob of
mercury inside a 40 kHz field. This has proven in past
machines to be highly reliable, and is the basic "Yikes!
Someone is touching me!" sensor. Like most car alarms these
days, it has a pocket remote control, and this little antenna
picks up the digitally encoded 300 MHz signal.

Cellular elevated feed whip (821-896 MHz)

The rear spot on the solar lid belongs to the cellular whip, an
elevated feed unit from Larsen with 3db gain. This has
slightly better than normal cellular performance due to the
extra height, but is nothing like the next item...

Cellular 6-element yagi (824-868 MHz)

You know how frustrating it is to be just outside cellular
service range, watching your NO SERVICE light flash in the
middle of a conversation? This fixes that problem dramatically
-- it's a 6-element beam with 10db gain, cut for the cellular
mobile unit's transmit frequency range. I've tested this to
about 100 miles on my Oki 491 with good results, and it is ONLY
for use when unmoving and outside a normal service area since
the radiation pattern can confuse the cell sites and frustrate
normal channel-management operations. (A more typical use is
to provide a cellular alternative to stringing wires for remote
home sites.)

GPS receiver (1.575 GHz)

Mounted in a little nacelle molded into the new fiberglass
fairing is an impressive bit of RF black magic, about 4"
square. This is the antenna for the Trimble TANS GPS
navigation receiver, receiving spread spectrum time code data
from a constellation of 24 satellites in circular orbit (about
17 are now in place). The antenna contains a 50db preamp
powered via the coax feedline, and the actual element is a
piece of thick glass-epoxy circuit board with a ground plane on
one side and a rectangle on the other... fed with a single pin
about a third of the way in from a corner. Something about
standing waves and circular polarization... like I said, black
magic! I call it my "here and now" box: when powered on, it
puts out a continuous feed of latitude, longitude, and
elevation (to about 100 feet); speed to .1 mph; and time to 1

Microwave security unit (10 GHz)

Moving up rapidly in the spectrum, we find a peak at 10 GHz --
belonging to the AM Sensors (formerly Alpha Industries)
microwave doppler motion sensor, the first level of security
monitoring. The feedhorn is mounted vertically, penetrating
the top of the RUMP and firing into what appears to be a fat
mounting base for the 7" yellow flasher. Inside is the hack:
a copper 90-degree cone with its apex at the exit aperture of
the antenna, resulting in a 360-degree radiation pattern around
the bike with a 48 degree spread from the horizontal.
Sensitivity is set to trigger a response when a person moves
within 10-15 feet (not necessarily an alarm condition, but good
to know).

Qualcomm satellite terminal (14 GHz)

Finally, up in the rarified ether of the Ku band, there is the
OmniTRACS terminal. More than any other single bike system,
this expresses the theme of this whole adventure: maximum
connectivity under all conditions, rendering my physical
location irrelevant via the magic of technology. (This system
is described a little more fully in Issue #8.) Inside the 12"
diameter white dome is a stepper-motor-driven feedhorn, curved
and shaped to yield a 5-degree wide by 40-degree high beam,
centered at 40 degrees above the horizon. This is driven in
azimuth by the controller, which monitors the signal from the
GTE GSTAR satellite for feedback. Occasionally it glances over
at a "tracker" bird to triangulate its own location within
about 1000 feet, automatically location-stamping all my
outgoing email. 1 GHz IF and REF lines connect the antenna to
the OmniTRACS main unit under the trailer's forward Thermoclear
subfloor. The net effect? 24-hour-a-day email connectivity,
hacked into internet via the Qualcomm hub in San Diego and a
Sun 3/260 that rewrites mail headers and otherwise manages tha
network hooks.

Phew. There. The only thing that scares me about all this
(other than the usual problem of hauling it up hills and the
potential for frying myself with some exotic blend of radiated
energy), is the effect on certain non-technical functionaries
who hold accept-reject power (and worse) at national borders.
Bernard Magnouloux, circumnavigating the globe the hard way via
bicycle (the length of Africa, the Length of South America,
across China, etc), was harrassed at some obscure African
border for being a spy. It was the high-tech equipment that
got him in trouble... a pocket shortwave radio like any of us
could put on the Visa card for about sixty bucks. I may have
problems with that someday...

"What is this?"

"Oh, just my satellite link. For email." I smile disarmingly,
hoping the guard will stop aiming his service revolver at my

"And this?"

"Ah, that. A high-speed packet data link for file transfers
between the bike and this little aluminum briefcase here...."

"I see. You will follow me. Keep your hands where I can see

Considering that I was harrassed for over an hour when bringing
the bike into Port Angeles, WA from its display at Expo in
Vancouver, this is not at all farfetched. Next version... the
stealth model...

Arthur C. Clarke observed quite accurately that "any
sufficiently advanced technology is indistinguishable from
magic." Where governments are involved, replace "magic" with
"national security risk." In a philosophical sense, of course,
that's quite true... is there anything that shows LESS respect
for artificial national borders than radio waves?

Nifty Regulators

This issue is getting long, but there is one more thing I
really have to tell you about. You know those ubiquitous
3-terminal regulators that have been around since the early
1970's -- the 340 series and its various cousins? They're
handy but horrendously inefficient, burning away the difference
between input voltage and output voltage in the form of heat,
linearly related to the load current. Obviously useless for an
application such as this where power is a scarce resource.

Switching regulators have been around for years, of course, but
have a well-deserved reputation for being difficult to
design. Chips from Maxim and Linear Technologies go a long
way toward making life easier (and are still the best approach
for really fine-tuning and cost-optimizing a low-power switcher
design). But haven't you just ACHED for something quick and
easy, like a drop-in 3-terminal regulator replacement that
doesn't require you to think about inductors and catch diodes?
Ah, I thought so.

Well, now there is one. The 78SR series from Power Trends is
just that -- slick little 1.5 amp 3-terminal modules that make
efficient power supply design about as easy as GROSS power
supply design was back when we didn't know any better. They're
available in 5, 9, and 12 volt models, are short-circuit
protected, draw about 6 mA quiescent, accept up to 30 volts in,
and run at about 90% efficiency with loads above 100 mA or so.
Implementation is trivial -- an input electrolytic to slow the
rise time of a fast power switch, an output cap to reduce 650
kHz ripple (seems pretty optional -- I don't even notice the
effects when running radio gear), and in some applications a
zener to clamp the output in situations when the input voltage
rise time is extremely short. That's it. They work
beautifully, and are being scattered all over the bike to
produce regulated voltages from the 12-volt battery bus.

Check 'em out... the company is Power Trends in Batavia, IL.

Cheers from the Bikelab!