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The Slinky that became a Antenna

Helitrix the ideal Indoor Antenna

ONLY  $29.95

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 moments.
    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 $29.95
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.

Includes Feedline

Helitrix 40-10M Indoor Antenna             $29.95US  
Helitrix Extension for above 80-10M       $8.95US  
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Last modified:  April 17, 2014