To: [email protected]
Copyright 1998, Virginia ARES,
Nonprofit reproduction is permitted with attribution
C. Edward Harris, KE4SKY, AEC Fairfax ARES
When limited to "barefoot" operation, with a
"rubber duck" on simplex, HTs are not adequate
as a primary rig for emergency communications.
I started with an HT when I first got my license. I
now recommend 50w mobiles as a first rig, but
admit they don't work for everyone. If all you have
is an HT, the following will help you to "make the
most of it." An HT does make perfectly good sense for:
National Bureau of Standards tests of Public Safety high band
and amateur 2-meter antennas indicate that a "rubber duck" has
-5db, "negative gain" compared to a quarter wave held at face
level. In terms of effective radiated power (ERP), this means
that a 5w HT with rubber duck, radiates only 1 watt. Placing an
HT on your belt results in another -20db attenuation, reducing
ERP to 50 milliwatts! UHF results are no better...
This simple helical spring is intended to withstand rough
handling, but is not indestructible. Flexible antennas used on
fire lines for several weeks showed a 60% failure rate. The
California ACS recommends that flexible antennas be replaced
annually or more often if they show any apparent kinks,
abrasion or other wear to visual inspection.
A simple, inexpensive and effective expedient to improve a
"rubber duck" is a counterpoise or "tiger tail. Make this from a
quarter-wave piece (19.5" on 2m, 11.5" for 220 and 6.5" for
440) of stranded wire, crimped and soldered to a battery clip.
Always reinforce the soldered connection with heat shrink
tubing or tape to resist flex. When clamped to the outer collar
of the BNC connector on your HT antenna, the counterpose
prevents RF from coupling with your body, so your antenna acts
like a center-fed dipole instead of an end-fed dummy load! In
marginal conditions extending the counterpoise horizontally,
pointing your hand to steer the radiation pattern where you need
it, produces a dramatically stronger signal than letting it "droop."
Several HT antennas are commonly available which perform
much better than the standard helical "rubber duck." Flexible
1/4 wave and telescoping 1/2 wave antennas work very well. A
quarter wave provides unity gain when used with a "tiger tail"
or counterpoise and held at face level. This simple device
represents a 5 db improvement over a typical rubber duck,
because most of its effective signal is radiated. If using the HT
in a vehicle, use a mobile mag-mount antenna to provide an RF
path outside the vehicle. This overcomes the -20db attenuation
which otherwise results from operating your HT with a rubber
duck antenna inside a metal vehicle. Always carry a male BNC
to female UHF adapter so that you can attach your HT to a base
or mobile antenna, when one is readily available.
In marginal operating locations a telescoping half-wave is a
better performer, because it provides the same unity gain
without a ground plane that a 1/4 wave does when used with a
ground plane. A 1/2 wave antenna can be pulled up into a tree,
dangled out of a window, attached to a window pane with
suction cups, or be used bicycle or motorcycle mobile, or in city
driving on a window clip mount. Adding a ground plane or
counterpoise to a 1/2 wave produces about 2 db of gain. A
telescoping half-wave boosts the readable simplex range of a
typical 5 watt, 2-meter HT from about a mile with a rubber duck
to 3 miles or more, depending upon terrain. Adding a tiger tail
improves receive and extends simplex range up to about 5 miles.
Telescoping antennas are more fragile and work best when
stationary or in the open, avoiding side impacts or rough
handling. Avoid prolonged mobile use of telescoping antennas
on mobile window clips at highway speed, because excessive
flexing loosens the internal electrical connections. Never
collapse a telescoping antenna by whacking it down with the
palm of your hand. Gently pull it down with your fingers. If
you note any wobbling or looseness, replace the antenna.
Flexible antennas are safer when working in close quarters
around people and are more durable when walking through
dense vegetation for wildfire suppression or search and rescue
operations. They a better choice for dual-banders because most
telescoping antennas are single-band. Most common dual-band
flexibles approximate a 1/4 wave on 2 meters and a 5/8 wave on
70 cm, are optimized for one band and may resonate poorly on
the other. Some antennas do perform better than others, but how
efficient a particular antenna is can be determined only by testing.
If you want to buy one emergency HT antenna, without risk or
experimentation a telescoping half-wave, flexible dual-band
quarter wave; or half-wave, dual-band-mobile magnetic mount,
which will work without a ground plane, offer the best "bang for
the buck." Whatever HT gain antenna you get should be able
to handle 25W so that it can also serve as an emergency mobile
antenna or be used with a brick amp. In our group experience
the Comet CH-72 and SBB-1 dual-band flexibles, rated for 50w,
work well. Adapters enable either to be used on an HT, attached
to a mag mount or pulled into a tree with an attached tiger tail and
coax leading from a mobile or brick amp.
A mag-mount works best on a car, but an improvised ground
plane can almost always be found around the home or office,
such as a metal filing cabinet, metal trash can, cookie sheet, rain
gutter, refrigerator, window air conditioning unit, balcony
railing or any other large metal object. On bikes, motorcycles,
Humvees or ambulances with fiberglass caps use a half-wave
mobile antenna which doesn't require a ground plane.
The most common operator error working public service events
is failure to carry enough batteries to last all day. Always carry
two fully charged NiCd packs AND an extra AA battery case, so
that you can keep operating if you can't recharge your nicads.
Cycle and recharge dry nicad packs every two to three weeks.
Write the recharge date on a strip of tape on each pack. In cold
weather it is important to keep NiCd packs warm by keeping
them in an inside coat pocket and not exposed on your belt.
Adapter cords enabling you to take power from an auto cigarette
lighter plug or a gel cell battery are needed for extended
operation. Cigarette lighter plug cords are often unreliable
because the sockets are often contaminated and not the best
conductors and they very in size so that the plug may vibrate
loose,. As an alternate power source you should still have one,
because they are ubiquitous and in a pitch much better than nothing.
Auxiliary power cords to power your HT and small brick amp
from an external gel call battery should follow the wiring
configuration shown in the ARRL ARES Resource Manual.
Use twin lead AWG12 to AWG16 gage "Zipline" with Molex
Series 1545, 2-pin polarized connectors and .093 pins. In ARES
practice the female pins are assembled into the male plug which
is attached to the power source and the male pins into the female
receptacle which is attached to the rig. The plug, receptacle and
pin set is $0.99 from Radio Shack, Part No. 274-222, rated at 8A,
which is adequate to power small brick amps up to 35w output.
Tech America carries the genuine Molex parts in bulk, which
are rated at 11 amps and suitable for bricks or mobiles up to 50w.
Wiring is simple. The end of the two-conductor Molex plug in
cross section resembles a little 2-story house with peaked roof.
Remember proper polarity by the word associations "red roof"
and "black basement," or "pointy positive" and "flat black."
Crimp wires before soldering to ensure a strong connection.
After inserting the pins into the plug and receptacle, check fit of
the assembled fitting and reinforce the wires behind the plug and
receptacle with heat shrink or tape. On the battery ends attach
crimp type .187" female tab terminals to fit the male tabs on the
battery. Wire a plug receptacle onto the leads of a 12-14V,
250mah-500mah wall transformer and for normal charging use
a time and current to equal 120% of the battery's capacity.
You can rig two sets of cords directly to your car battery to
power an HT and your brick amplifier without using the
cigarette lighter plug. This works well for commuters who use
an HT in the car and take it with them after they park. Splice
AGC type fuse holders onto both leads, as close to the battery
as possible. Use 2 amp fuses for the HT and 10 amps for brick
amps up to 40w. Use different wire gages such as AWG16 for
the HT and AWG12 for the brick amp, so that the two different
cords are readily distinguishable by sight and feel.
If compact HTs are subjected to frequent 5w transmissions of
several minutes, they overheat and the final power transistors
may fail prematurely. Kenwood and Yaesu state that their HTs
are rated for 20% duty cycle at 5w PEP, or 30 seconds transmit
to 2 minutes of standby. This is not common for today's Hts.
When I first got my license, I burned up three sets of "finals"
during the year warranty period, powering an HTX-202 from an
auto cigarette lighter plug.
After the warranty ran out, I replaced it with a Kenwood
TH-22A and within a few months repeated the same
result. Kenwood's Virginia Beach service center politely
admonished me that I was "exceeding the recommended duty
cycle" for a hand held and should buy a mobile. I followed their
recommendation, sought other HTs for ARES /RACES
/Skywarn and now pass that advice along.
Of the popular 2-meter HT's, only Standard doesn't restrict duty
cycle and warrants their amateur hand helds equal to their
commercial, aviation, marine and public safety band portables.
Unless your HT is a Standard, old Icom "brick" or "pre-tiny"
Yaesu, use low or medium power most of the time to save your
finals and limit your full power 5w use to short transmissions.
If you have need for high power transmissions of several
minutes duration and can't replace or supplement your hand
held with a mobile rig, my advice is to get a brick amp to do the
heavy work. This keeps your HT from overheating, and helps
ensure a solid copy signal for emergency simplex operation.
An ideal amp for HT owners to upgrade portable ARES or
RACES equipment at modest cost should weigh under a 1=BD
pounds, be capable of 10 to 15w output when driven by an HT
at =BD to 1w, or 20 to 40w output when driven by the same HT at
its normal 2 or 3w output from a standard NiCd battery pack. It
should draw no more than 8 amps current at its maximum rated
output, enabling it to operate safely from the .093 pin Molex
Series 1545 connector or fused cigarette lighter plug.
An FM-only brick without a preamp is best, because a preamp
brings in intermod on FM. Small brick amps we have found
satisfactory for ARES are use the Diawa 2035, Mirage B-23, B-34,
dual-band BD-45 and Rf Concepts Mini 144. There are larger amps
producing 100+ watts output when driven by an HT, but their
size, 5+lb. weight and 20+ amp power requirements lend them
more to contesting than to "backpack" portable ARES or SAR
use. Be wary of, "no-name" amps at hamfests or in discount
catalogs. Many are not aligned for the U.S. 2-meter band, lack
protection for over voltage, overdrive or high VSWR or have
inadequate heat sink so they overheat and simply quit. Seek a
quality amp with ample heat sink, of a known brand which
stands behind the product, rather than the smallest "box" at the
lowest price.