The Broomstick Special,
Host of "Dxers Unlimited", Radio Habana,
A few more tips on how to optimize this simple linear mode
If you have
built and tested my "broomstick" helical linear mode antenna,
using the data supplied in the first article, you should have
The antenna performs quite well even without an antenna tuner
When used with even the simplest LC tuner in an L network configuration,
the "broomstick" is quite competitive with any other indoor antenna.
You have by now realized that this is about the cheapest and easier
to build antenna!
2 then? Well, because there is always room for improving an already
ago amateur radio magazines carried a rather small ad about a
so-called Joystick VFA antenna... made in England. With the ad
came some rather amusing claims about DX worked... which happened
to be true! The Joystick VFA was nothing more than a helically
wound antenna... and it worked!
is a little bit more simple... but as I said, you can improve
it in the following ways:
Install a counterpoise or ground system. This may be as simple
as a single wire coming out of the antenna tuner and extending
from 5 meters to 20 meters ... it need not be installed in a linear
fashion, I have used this counterpoise system with the wire tacked
to the wall around the room!
Resonate the antenna's main helical loading plus
its extension to the operating frequency, something that requires
patience, a Grid Dip Meter, more patience, and then a good, high
quality standing wave ratio meter.
Install the antenna outside, and connect it to the antenna tuner
with a single wire feedline made of no 14 or no 12 copper wire...
You want this wire short, at least as short as possible,
and you must be really careful how it travels from the base of
the Broomstick to the antenna tuner. You want to avoid a bad
RF burn if the antenna's lead in touches someone's skin!
If you choose no 3 approach, then you must resonate the
combination of single wire feedline plus Broomstick to
the operating frequency, something that may turn to be especially
critical when using the antenna for transmitting, but that is
not so critical if you are using it for receiving only!
Broomstick antennas are excellent club projects, as they can be
mass produced at very low cost... especially if you buy materials
in quantity. The use of PVC plumbers pipe, the white colored stock,
works quite well with transmitters in the 100 watt class, but
don't use it if you ever intend to run higher power. High
power - i.e. more than 100 watts should be avoided with the Broomstick!
antenna made with a 2-meter section of 25-mm diameter plumbers
PVC pipe, terminated with a 30-cm diameter top loading disk is
the minimum I would use for transmitting. Ideally you should try
to use no less than 2.5 meters, but many modern buildings will
not be that high ! Please do remember to use the antenna for transmitting
only if it can be safely placed, as far as possible from you and
any other persons or animals in the room!
distributed loading can be optimized a bit by winding it with
different pitch.... starting with turns separated about 2 wire
diameters at the base, going to one wire diameter separation at
the middle, and ending with closely wound turns at the top of
the antenna, were it connects to the aluminium top capacity loading
disk.The general rule to follow is to wind enough wire so that
it makes a half wavelength at the lowest operating frequency
you want the antenna to work... Example... for a "Broomstick"
designed to operate from 7 MHz up, the wire length should be no
less than 70 feet. It's always a lot easier to remove a
few turns at the top, than to have to splice the wire and then
add a few more turns!
the distributed loading works better, but it is really difficult
to tell the difference when using the "Broomstick" in actual practice!
PI network tuner works very well. For RO (receive only) I use
two old capacitors from defunct vacuum tube radios, connecting
only the 365 pF sections.
is made also from PVC pipe... I use a 40-turn coil wound on a
25-mm diameter PVC pipe, I tap the coil every 5 turns, and use
an alligator clip to select the best tap for the frequency I want
to operate. You can add a wafer switch (ceramic is best if transmitting)
to select the taps at the coil... a 10-position switch is ideal,
but you can do well with a 6-position one, too.
6 February, 1998
from Arnie Coro on Radio Havana Cuba