A SHORT VERTICAL FOR THE TOP BAND


                               BY


                          Phil Scovell

                              K0NX





     Soon after purchasing a transceiver with 160 meter
capability, I decided to go for the Top Band.  At that time, I was
renting a bi-level duplex with the smallest backyard I had ever
seen as a ham.  It was only about 30-by-40 ft. and the front yard
was even worse.  To complicate matters, I had 38 ft. of Rohn 25G
bolted to the back of the house at the 14 foot level, with a
single set of guys at 35 ft.  Perched on top was a 4 element 20
meter yagi on a 24 ft. boom.  The tower itself was simply too
short to shunt feed and a 160 meter inverted L was out of the
question.  Even an adequate ground system in that limited space
was impossible.  I did the only thing left to do - made a short
top loaded vertical.

     Most of us have always considered 160 meters to be limited to
those with miles of open range and super tall towers.  Few, in the
city, have much more than 260 ft. of yard space, the needed
length for a half wave on 1.8 MHZ, or even enough room; not to
mention the money, for a 130 foot tower - the length of a quarter
wave for 160 meters.  For those of us with small yards and even
smaller towers and limited budgets, there is no hope?  Not so!  My
vertical was only 32 ft.

     Short top loaded verticals for 160 are commonly used and
their advantages are numerous.  Conveniently, they need almost no
ground.  The nicest thing about top loaded verticals is their
radiation pattern:  The antenna radiates from the top instead of
the bottom; thus allowing the signal to be projected from above
ground where it does the most good.

                          CONSTRUCTION

     Using the remains of a telescoping push-up mast from Radio
Shack, I bolted 24 ft. of vertical mast to the peak of the duplex
on the west side of the house at the 20 foot level.  Sandwiching a
piece of plastic between the house bracket and the edge of the
roof helped insure the antenna was adequately insulated.  My
telescoping mast was once about 40 ft. but only 24 feet remained
after a 100 MPH plus wind storm - you use what you have.

     Setting the mast on a block of wood, again using a piece of
plastic for insulation, I planted the antenna.  The braid, shield,
goes to ground.  Your ground can be, as in my case, a nearby chain
link fence, or a ground rod, or even a cold water pipe.  If there
is room, lay out as many wires, no matter how short, as you can;
and attach your shield to the wires.  The larger the diameter of
wire, the better.  Yes, you can use insulated wire; in fact, it is
preferred if you plan to bury it.  The center conductor goes to
the base of the antenna.

TOP ASSEMBLY

     The top of the vertical was made up of A:- 4 ft. of 1 inch
aluminum tubing, B:- 3 ft. of 2.5 inch plastic tubing: PVC pipe,
and C:- an additional 7 ft. of 1 inch aluminum tubing.  I used 2.5
inch diameter PVC for my coil form because I had no idea how large
a 160 meter resonator should be.  Later, of course, I discovered I
could have gotten along with something smaller.  Learning is what
home brewing is all about.

     I bolted both the 4 ft. and 7 ft. pieces of aluminum tubing
to either end of my 3 ft. PVC pipe - a few inches down inside
either end to insure structural strength - the 4 ft. length on the
bottom and the 7 ft. poking out the top..

RESONATOR

     The coil, or the 160 meter resonator, was a winding of 14
gage insulated wire rapped around the middle of my PVC pipe.  How
much wire did it take?  I wanted my antenna to resonate near the
bottom of the band, 1800 KHZ, since I was mostly interested in CW.
A quarter wave at that frequency is 130 ft.  The total length of
my vertical, I judged, would be about 32 ft; so I wound the
difference, 98 ft., around the plastic pipe and tied the ends of
the wire to the bolts used to secure the aluminum tubing to the
PVC coil form.

     HIGH VOLTAGE

     The voltage on such a coil is very high.  If high power is to
be used, a heavier insulated wire, such as RG8U, should be used
for the winding to prevent arcing.  Some hams even used quarter
inch copper tubing wound on a coil form when running a KW.  My 100
watts, however, presented no such problem; thus the 14 gage
insulated wire was satisfactory.

End of part 1 of 2



Phil C Sharp
The Coil Of The snake
A Free Online E-Novel
www.SafePlaceFellowship.com