BUILD THE J BEAM FOR 2 METERS AND
Condensed from an
article by Ed Bathgate, N3SDO as published in CQ VHF Magazine July, 1988
and used with his permission. Thanks Ed!
"Recently, while going
thru some of my older Ham magazines,
I ran into this article by Ed,
N3SDO on the J BEAM antenna.
It struck me that some of you out there
may not have seen this fantastic project or maybe you do not get CQ VHF
magazine, which is back now better than ever!
A little research
on the web indicated that there is not much information on how to build
the J beam antenna that is useable with clear graphics and good plans, so
I contacted Ed, and after signing my XYL, car, home, bank account with
$73.73 in it and all my good looks over to him he finally gave us the
needed permission to put the plans on this site for all of you to
Thanks again Ed!".............N4UJW
LET'S GET STARTED
Now you've probably heard of a beam antenna, and maybe you've heard
of a J-Pole.
But what's a J
It's a vertical directional antenna made of 1/2 inch
copper pipe and wood or PVC. It uses a standard J-pole antenna as the
driven element and center support, with two parasitic elements-----a
reflector and a director, to provide directivity and gain. See
J Beam pattern
below. It can be built for around $15.00 (1998 prices) and
you can use your old Jpole as a basis for the JBeam. You'll probably need
to shorten the main 1/2 wave element by 1 to 2 inches, as the reflector
and director tend to couple and lower the resonance of your original jpole
toward the lower part of the band. See formulas for cutting to your
desired frequency of operation or band . A small amount of trimming on the
tip of the main active 1/2 wave element may be needed to get the SWR as
low as possible.
You shouldn't have to adjust the 1/4 wave matching
stub, as this is not strongly affected by the parasitic
Design Details and Drawbacks
element lengths and spacings are a combination of info from the ARRL
Antenna Book section on 2 meter Yagi antennas, and from experiments with a
field strength meter and different length elements and spacings.
reflector and director element spacings are equal at 16 inches. Slightly
higher gain with reflector spacing at 18 inches from driven element and
director spacing of 14 inches can be had but the antenna may tend to lean
with unequal spacings if strong mast mounting is not used.
bandwidth is not as wide as that of the standard jpole by itself. The SWR
tends to rise faster toward the ends of the band, but you get an estimated
7dB gain and 20 dB F/B (front to back ratio).
High wind loading could
potentiallly break off the jBeam at the bottom joint since the entire
structure is supported by that point. You may want to reinforce
The lengths used in these plans are for the upper part of 2
meters and you can use the formulas to design it for your
1/2 inch copper pipe is used for all elements and standard
soldering made with a small blowtorch. A soldering iron is just not hot
Longest element = 58 1/2 inches (add about 2 feet for
mast mounting) matching 1/4 wave stub = 20 1/4 inches
- 40 inches
Position matching stub toward director for a bit of
added gain reflector
director = 32
Stub and main
element spacing = 3 inches
Some examples for other bands:
Coax feed point = 3 to 5
inches from bottom
(use hose clamps for feed point
coax attachment connections for easy
Center boom is 1/2 inch by
1-inch wood or PVC and about 36 inches long
Measurements should be made as close as possible but are
not extremly critical!
Element to boom mounting variations depend on
your particular situation and construction materials at hand but insure
that element centers are at center of boom Use your own imagination! (see
pics for better details)
"One fellow built one with five
elements-----just cutting the extra directors shorter by eye-----and was
able to work a repeater 35 miles away, with a 5-watt HT holding the
antenna, from a valley that's hard to get out of with 50 watts and an
omnidirectional antenna at 30 feet!"........Ed Bathgate
J Pole Long element (in Inches) = 8568 / F mhz
Stub (in inches) = 2952 / F in mhz
Reflector (in inches) = 5880 / F in
Director (in inches) = 4704 / F in mhz
Spacing (in inches) =
2352 / F in mhz
REF : 26.52"
PICTURE IS WORTH A THOUSAND WORDS"
Here are two thousand
Notes: Make driven element about 2 feet longer at bottom for mast
Center conductor of coax to longest element, shield to
Red circle is pattern of standard omni J
area is estimated pattern of JBEAM
using field strength meter
MORE J POLE
USING HO SCALE TRAIN TRACK ON 2
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