Fun with Helitrix , the stretchy helix.-- Helitrix is a flexible springy
helix with a 2-3/4 inch diameter. Each Helitrix weighs approximately 7 ounces. When
collapsed it is only 2-1/4 inch long, but it can be stretched without deforming into a
helix as long as 15 feet in length. An antenna made from a Helitrix is light, simple
to suspend and extend, and easy to put out of sight when not in use.
Helitrix Antenna Basics.-- For a forty meter dipole, use a full
Helitrix coil on each side of the feedpoint. Stretch to 15 ft. For 75 meters put two
coils on each side and stretch the whole to about 30 feet in length. Presto! You will have
an 80 meter dipole that fits in most attics or even in a motel room. A quick twenty meter
dipole, can be made by stretching out a single coil to a length of 7 ft and feeding it
with a delta match in the center.
Helitrix Antenna Performance.--Is Helitrix a wonder antenna? No. But it
works. In a test on a state-wide 75 meter phone net, a 30 foot 80 meter Helitrix
dipole at 20 ft received signal reports on average 1-1/2 S-units lower than a TNT Windom
at 35 feet. That's not bad for a 1/8 wavelength antenna. The Helitrix dipole would have
compared better had it been equally high, but it would not outperform the full size
dipole. On the same occasion a comparison was made with a Hustler mobile whip. Compared
with the whip, Helitrix performance and bandwidth were outstanding--better by several
S-units for state-wide coverage. So, considering that you can even install a Helitrix
antenna for 80 meters inside a motel room, the Helitrix antenna promises some good
1. The simplest way to obtain multi-band results is to take a pair of
Helitrix coils, one on each side of your feedpoint, stretch them as far as space
permits, and clip on the feedline. Here you have a compact version
of the good old "center fed Zepp". Feed it through an antenna tuner. This simple
antenna will play on all bands 7 MHz and above. In a pinch it will permit QSOs on the 80
meter band. The ready-to go QRV Helitrix 40-10 antenna (see description below) is an
aesthetically pleasing and easy to use version of this basic doublet.
2. Helitrix antennas are best suited to indoor or portable
deployment. If you wish to put your Helitrix antenna outside on a more or less
permanent basis, you should solder all connections well, then paint the whole antenna with
spray enamel. This is actually quite easy to do, so don't shy away from trying it.
3. For a given Helitrix antenna, performance is best at the
frequency of natural resonance and on the next harmonic because the coils act increasingly
like an RF choke on the higher harmonics.
Have Fun with a Helitrix! But be careful the kids don't run off with
it. They could slink around with it like a toy. But they'd miss the big fun. Could they
imagine talking into one and having someone from Japan answer them on 15 meters? Or think
of checking into MARS and RACES nets with a Helitrix on the bedroom wall? Only in
amateur radio can you get a bang like this out of a stretchy helix.
Antennas & More has put together what you need to get off to a fast start
with Helitrix experimentation. Check out the items listed below and turn a weekend
with a Helitrix into the most fun you've had since you were a kid .
Helitrix Antenna TechNote 123D $7 ppd.
This frequently updated Technote reviews Helitrix experiments performed to date.
Gives detailed information on the electrical properties of Helitrix coil antennas.
Describes instruments used & designs tested. Reports unpublished experiences of
numerous contributors. Shows how to get the most out of a Helitrix with or without
an antenna tuner. Reviews what works and what doesn't. Use this to study out the
principles and plan your installation. QRV Helitrix Dipole
This is the fully refined and ready to use QRV Helitrix system, all set to go for
instant motel, attic, or portable use. Coaxial feedline.
Quick attachment clips make it a snap to hook up fast. Support line lets
antenna slide in and out of action instantaneously. Unique design assures unerring and
quick return to correct position whenever desired. Mounting tabs, coax feedline, and unobtrusive installation easy, whether for long or
short term utilization. Manual shows proven methods for working 40 thru 10 even without an
antenna tuner. With tuner work 80 meters.