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 The
Super J Pole antenna is a co-linear vertical consisting of a number
of half wave length vertical elements separated with half-wave
length stubs (Tuning stub) feed with a folded matching stub. The sub
doesn’t
receive or radiate any energy; it is simply a way of picking off the
desired feed impedance.
Additional half wave length section
can be added with addition of a half wave length tuning section
(Tuning stub). The addition of half vertical elements could be added
indefinitely, subject to reality of diminishing returns. This
arrangement can be applied practically and usefully on bands within
the VHF and UHF spectrum. The use of the J pole feed arrangement
creates an antenna that is relatively ground independent compared to
many other designs.
DIAGRAM
OF THE SUPER J-POLE
Frequency:
435Mhz
Polarisation:
Vertical
(A)
Main element:
502mm
(0.75 Wavelength x 300/f
x k)
(B)
Matching stub:
167mm
(0.25
Wavelength x 300/f x k)
(C)
Additional section 349mm
(0.50 Wavelength x 300/f
x k)
(D)
Tuning stub:
349mm
(0.50 Wavelength x 300/f
x k)
(E)
Feed point:
Approximately 10 - 30mm from the bottom.
Subject to adjustment for lowest VSWR
The
dimensions of the Super J-Pole have been determined as follows:
Length (Mtr) = 300/f x k x el
f
= Operating frequency e.g. 435.5MHz
k
= The effect of the diameter of the material in relation to the wave
length
(0.97)
el
= Chosen element e.g. Wavelength
main element, wave tuning stubs
or wave matching
stubs,
0.75, 0.50 or 0.25 respectively.
The
associated photos are of my successful in service (2001 – 2006)
version that covers the entire 70cm (430 - 450 MHz) band.
Practical
construction
Construction is very simple. After
determining the various element lengths, mark them out accordingly
on a continuous length of copper wire and bend to achieve the
antenna shape. The tuning section that separating the additional
half wave length elements can be bent around to form a semicircle
(see photos). Tape the wire formed antenna to a suitable length of
dowel or fibreglass rod for stability.
After successfully impedance matching
the coax feed point with a VSWR meter the antenna can be mounted
inside a suitable length of conduit to protect the antenna from the
effects of weathering.
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