2 METER/440 DUAL BAND SLEEVED DIPOLE
MODIFICATION
BY
W7LPN Rick Frazier
The photo
above is of my balun modification of the QST August, 2006 page
50,
2 Meter/440 dual bander sleeved dipole by Geoff Haines, N1GY.
He is credited with original article in QST magazine.
The original
sleeved dipole project idea is from Harold Melton
KV5R.
N1GY Improved upon his
design.
I took it one step further by
changing the location of the balun.
The
only Mod I made to it other than personal choices of similar
materials
was the placement of the Balun as shown in the picture above.
Otherwise it is essentially the same as the original design.
I
modified it to place the balun around the PVC at the base just below the
lower element. In the original QST article design by NIGY, the balun was
about 12 inches below the bottom of the PVC. By placing the balun ON
the PVC as in the picture, this has significantly improved it’s
function and apparently lowered the take-off angle. I can now hit
repeaters behind hills 70 miles away.
Before the mod, I could not hit a
repeater 40 miles away in the open on top of a tall hill. I believe this
was due to the steep take off angle previously of the original article
design.
My alteration to
QST's sleeved dipole, I believe, prevents the extra coax from attempting
to be part of the lower element and resonating, throwing off your SWR on
440 and raising the antenna pattern. The balun works double duty here. I
can tell my signal has a much lower Take-Off angle now than before because
I can hit repeaters consistently further away than I could before this
alteration. I had very strong signals close by with both designs, however,
with the new placement of the balun, the distant repeaters are now much
clearer.
In fact, one repeater that I talked on repeatedly with my
W7LPN Vertical Copper Tubing & PVC Dipole, seen in another
project, was unreachable with N1GY's design. After my mod, I can
reach it full quieting at over 80 miles thru uneven
terrain.
The basic design is
from August, 2006 QST magazine., but I wrapped the balun around the PVC
just below the lower element, NOT underneath the antenna on the
mast.
That's too far
and the tail of the coax will radiate, messing up the pattern and swr
on 440.
Here is a
simple drawing of the construction of the 2 Meter/440 Sleeve Dipole as
modified by W7LPN ~~~ Notice the balun is very close to the bottom
element, not down on the
mast!
ERROR NOTED
IN THE ORIGINAL N1GY QST ARTICLE!
Upper element length is shown at
two different lengths in Figures in article!
Figures 2 and 3 show
22 1/8 inches
Figure 4 states 21 1/8 inches as does the drawing above
(taken from figure 4)
It is suggested that
you use 22 1/8 inches and trim if
needed
Here are some added tips!
I had an idea for the sleeved dipole for a cleaner looking
finished project.,
and no visible coax wrapped or electrical
tape.....
Put ferrite cores inside a short, larger diameter
piece of PVC just below the lower element and then neck it back down to
keep them in place and allow space for a mounting stub below
it.
