The Broomstick Special, Part 2

By Arnie Coro
Host of "Dxers Unlimited", Radio Habana, Cuba

A few more tips on how to optimize this simple linear mode helical antenna:

If you have built and tested my "broomstick" helical linear mode antenna, using the data supplied in the first article, you should have noticed that:

A.
The antenna performs quite well even without an antenna tuner

B.
When used with even the simplest LC tuner in an L network configuration, the "broomstick" is quite competitive with any other indoor antenna.

C.
You have by now realized that this is about the cheapest and easier to build antenna!

Why Part 2 then? Well, because there is always room for improving an already good design...

Many years 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!

The "Broomstick" is a little bit more simple... but as I said, you can improve it in the following ways:

1.
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!

2.
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.

3.
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!

4.
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!

5.
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!

A Typical Installation

A "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!

The helical 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!

Yes, the distributed loading works better, but it is really difficult to tell the difference when using the "Broomstick" in actual practice!

About tuners!

A simple 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.

The coil 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.

Radio Havana, Cuba
6 February, 1998

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