rf - Free and Open Source Software

•
A
Kilowatt
Dummy
Antenna
• • •
Cheap!
Allan H. Matthews, WB2PTU
R. D. #J
Waverly, New York 14892
This article describes a dummy antenna
capable of handling one kilowatt, to be built
at a cost of under $4 .00. In my case it cost
$1.53, but that was with a junkbox.
In a back issue of 73 (w here else?), there
were some 100 ohm, non-inductive resistors
advertised by Mendelson Electronics, 516
Linden Ave., Day ton, Ohio. I ordered two
of these at 50¢ each for my dummy load.
When they arrived, they were 3/4 inch in
diameter and 6 inches long, with both ends
tin plated. I do not know the power rat ing
of these resistors hut they are more than adequate
for our use. This unit will handle
over 100 watts PEP with no oil.
The photograph tells the story. The top
and bottom plates were cut to dimensio n,
punched and drilled first. Next the resistors
are fitted into the outside holes of these
plates and soldered into place. I used 1/8th"
double copper clad glass epoxy board and
soldered the resistors to both sides of the
board. Next run a heavy wire down through
. OO~ :*::
O-IOMA
100 OHMS
100 OHMS
B
the center hole of the top plate and into the
small hole of the bottom plate. Solder it on
both sides of the plate. Center this wire in
the top plates center 3/4" hole.
The next step involves a gallon paint can
which can be purchased empty and clean at
many paint stores for about 50¢. Punch the
top of the can for a coax fitting, drill the
holes to mount the unit inside th e can and if
you want a relative power output attachment,
drill holes for the feed -thru terminals
you will usc. Also, drill I extra 1/16'· hole
in the top of the can.
Mount the top plate hanging down fro m
the top of the can on 3/4" metal stand-offs.
The resistors will clear the bottom of the can
nicely at this height. Now mount your coax
connector. your feed-through termina ls and
the other components in place and solder
them. Run a couple of copper braids. (coax
shield) from the top plate to the top of the
can and solder them well on both ends.
They will help to provide a lo w impedance
ground path. The diode I used was of doubtful
ancestry, but a I N34A shoulu do the
trick . This relative output meter circuit
allows use o f a fairly heavy meter. dependent
upon the power of the transmitter and the
frequency of operation. A variable resistor
across the meter will be an aid.
Now go to th e power company and
scrounge a gallon of transformer oil or fill
the can with mineral oil . leaving about 1 and
1/2" of space at the top of the can. Do not
use motor ott'! The extra 1/ 16" hole? Oh,
that is to relieve pressure as the oil heats up.
When not in usc. plug it with a match stick
or small bolt. Well, there it is. a kilowatt
dummy antenna at a price everybody can
afford.
...WR 2PTU
92
73 MAGAZINE