[KYHAM] KEN Training for August 26: Hamstick Dipoles

[Ron Dodson]

Here is another thought provoker I found on the VARACES
Site. Thanks to the authors for their permission to use this
here.

(Disclaimer: Neither myself, KD4PWL or the owner of the
servers in use here promote the use of any one brand over
any other manufacturer's product.   
73, Ron, KA4MAP)

===============
Hamstick Dipole Is A Practical and Portable Limited-Space HF
Antenna
� 2001-2002 , Virginia RACES, Inc. - For Educational Use
Only

Authors Steve Cuccio, NB30, NM, Old Dominion Emergency Net
And Ed Harris, KE4SKY, VA State RACES Training Officer

When setting up portable or space restricted antennas,
stand-alone mobile whips are often avoided due to the lack
of a good grounding method.  Stringing ground radials or
using a ground rod in the field or the attic becomes
increasingly difficult.  While using one mobile whip by
itself requires a good ground or counterpoise (usually the
car body), a pair can be operated as a dipole.  Lakeview
(www.hamstick.com) makes a universal dipole mount for
$13.95.  They also supply quick-disconnect fittings with
3/8" X 24 threads which allow push-and-twist assembly of the
mobile whips to the dipole mount within seconds for those of
us wishing to make a quick setup or band change without
tools.

Pro-Am makes Valor HF linear loaded whips that disassemble
in half using a single threaded nut. This has the advantage
that tuning adjustment is not lost when the antenna is
disassembled.   Hamstick whips have two small set screws
that must be loosened to remove the stinger portion.  Both
brands cost about $24 per whip.  The eight-foot whip
disassembles to two four-foot pieces.  Each whip is designed
to cover one amateur band and can be adjusted from the phone
to the CW sub-bands by changing the stinger length.

The 2:1 VSWR bandwidth is narrower on the lower bands since
the whips are proportionally smaller compared to the longer
electrical wavelengths.  The 20-meter whips measured about
100 kHz, the 40-meter at 40 kHz and the 75-meter about 20
kHz.  If your HF rig has a built-in tuner, the useable
frequency span approximately doubles without significant
loss of antenna efficiency.

An on-the-air comparison was made between the portable whip
dipoles up 20 feet and half-wave dipoles for 40 and 75
meters.  On 40 meters, two whips were about 1-1/2 S-units
(about 10 dB) below the half-wave 40-meter dipole. Two
75-meter whips were almost three S-units (about 18 dB) below
a half-wave 75-meter dipole (no wonder, since a 75-meter
half wave dipole is 130 feet compared to the 16 feet of the
two whips). On 20 meters, we were surprised to see only
about one S-unit (6-dB) difference from a G5RV dipole
antenna.  Getting the portable whip dipole higher than 20
feet would also improve efficiency on the lower bands. This
portable dipole system was used to make contacts with
European Russia on 20 meters from a condo in San Luis, CA as
well as by Ed to San Juan Puerto Rico, Prince Edward Island
and Mexico City from the Pentagon south parking lot in
Washington, DC during the 2000 Marine Corps Marathon.  A
pair of Radio Shack 10-foot TV mast sections supported my
antenna parallel to the plastic rain gutter on the corner of
the house.  Bungee cords were used to hold it in place. 
Raising and lowering the antenna and masts to change bands
can be done by one person, but two make the job easier when
the wind is blowing. 

Ed uses four 5-ft. mast sections for ease of storage in a
vehicle. He recommends that whips all be equipped with
quick-disconnects, be color-coded by band and stored with a
4' ground rod in capped 3" diameter PVC pipe. RACES may need
to set up in a paved area such as an EOC parking lot.  To do
so bolt a folding 3-ft. TV roof tripod onto a triangular
support frame constructed of three 5' pieces of 1" angle
iron, using 1/4-20x3" bolts and wing nuts.  Similarly attach
a length of 2x6" across the open end opposite the TV
tripod.  Park a front tire of your vehicle on the board or
place sandbags across it to provide wind stability.  All
stash easily in an SUV.  With practice, you can erect the
antenna in 5 minutes! 

A variation provides dual HF band coverage with a single
coaxial feedline. 

Two hamstick dipole mounts were bolted together with their
center-isolated posts connected together using #12 gauge
wire.  Two sets of whips for 40 and 75 meters were
assembled.  Coax was attached to one of the mounts.  There
is minor interaction between the whips, although the #12
gauge wire looks slightly capacitive. Connecting the coax to
the lower band dipole mount reduces the effect of the #12
gauge wire.  A 25-foot length of coax was coiled at the base
of the mast as an RF choke to reduce any stray RF from
coupling onto the shield.  The same could be accomplished by
using ferrite beads on the coax feed near the dipole mount. 

Either arrangement provides a viable, convenient, portable,
horizontally polarized, high-angle antenna for NVIS
operation on 40 and 75 meters. It is also a directional
antenna on the higher frequencies, which is an effective
performer for those who live in antenna restricted
communities.  As with any transmitting antenna, be sure the
radiating elements, especially the stinger end sections, are
kept safely away from bystanders. 

73