Clandestine Dipole

Slinking Around: A Slinky is a toy made from a flexible 90-turn spring with a 2-3/4 inch diameter. Each Slinky contains 67 feet of flat steel wire, and weighs approximately 1/2 pound. When a Slinky is compressed it is only 2-1/4 inch long, but it can be stretched into a helix as long as 15 feet in length without deforming. An antenna made from a Slinky is light, simple to suspend and extend, and easy to put out of sight when not in use.

Slinky Antenna Basics: Since the 1950's, millions of people have had fun playing with a Slinky because of its mechanical properties. But it turns out that the Slinky has some interesting electrical properties at radio frequencies too. Since it is a helix made of conducting material, it will be self resonant at some frequency. In fact, a standard Slinky coil resonates as a quarter wave between 7 and 8 MHz when it is stretched to lengths between 5 and 15 feet. To tune the Slinky within that range one must only extend the coil to approximate size, then expand or contract it to reach the desired resonance. At a length close to 7-1/2 feet a standard Slinky is quarter-wave resonant on 40 meters. So a 40 meter dipole made from a pair of Slinky coils will fit in any apartment, balcony, or hotel room and can be put up in a matter of minutes. Dipoles resonant at frequencies above the 7-8 MHz range may be created by removing turns to shorten the helices or by shorting out turns. A twenty meter dipole, for example, can be made by cutting a Slinky coil in half or simply by feeding it with a delta match in the center. For target frequencies below 40 meters, one adds turns from another Slinky coil or clips wire pig tails on the ends. For example, by adding one more coil to each side and stretching the whole to about 30 feet in length, you can make an 80 meter dipole that will fit in most attics and motel hallways.

Performance: Is this a wonder antenna? No. But it works. In a test on a state-wide 75 meter phone net, a 30 foot 80 meter Slinky 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 1/10 wavelength antenna. It would have done better if the antennas were equally high, but it would never out perform the full size dipole. Compared with a Hustler Mobile whip, its performance and bandwidth were outstanding. So, considering that you can even install a slinky antenna for 80 meters inside a motel room, slinking around with one promises some good moments.

Tips for Experimenters Hereare a few things to keep in mind when working with Slinky coils.

1. The simplest way to obtain multiband results with a pair of Slinkys is to stretch them as far as space permits and clip on a feedline made of coax or twinlead. 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 and in a pinch it will permit QSOs on the 80 meter band.

2. Note that the coils will corrode if left outdoors for more than a few weeks. Corrosion will take place on the surface where the RF energy wants to travel. This means that the Slinky is really best suited to indoor or portable deployment. If you wish to put your Slinky antenna outside on a more or less permanent basis, you should solder all connections well, then paint the whole antenna with spray enamel.

3. Slinky coils are not self supporting so you need to use a messenger line to support the weight of the coils.

4. For a given Slinky antenna, performance seems 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 Slinking Around Kids don't know half the fun of a Slinky. 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 slinky on the bedroom wall? Only in amateur radio can you get a bang like this out of a slinky

AntennasWest has put together what you need to get off to a fast start with your slinky experimentation. Check out the items listed below and turn a weekend with a slinky into the most fun you've had since you were a kid . Slinky Antenna ProductsTechNote 123D $7 ppd. This frequently updated Technote reviews slinky experiments performed to date. Gives detailed information on the electrical properties of Slinky coil antennas. Describes instruments used & designs tested. Reports unpublished experiences of numerous contributors.

Shows how to get the most out of a slinky with or without an antenna tuner. Reviews what works and what doesn't.Slinky Experimenter Pack $13 Here's what you need to get started-a pair of slinky coils, a quick & easy center support, and the latest edition of Technote 123. Run your own experiments. Add $5 P & H.

QRV Slinky Antenna $35
This is the fully refined and ready to use QRV Slinky system, all set to go for instant motel, attic, or portable use Silver tipped coaxial feedline is decorator white. Quick attachment clips make it a snap to hook up fast.
Slick transparent support line lets antenna slide in and out of action instantaneously. Unique design assures unerring and quick return to correct position whenever desired. See-thru mounting tabs, ceiling hooks, and suction cups make unobtrusive installation easy- whether for long or short term utilization.

Manual shows proven methods for working 40 thru 10 without tuner. With tuner work 80.
Add $5 P&H. 80 meter Extension Kit $8 ppd Add-on coils for 75/80 effiecieny.QRV Slinky Gold Antenna $75 The ultimate in conductivity and beauty. Made with solid brass coils and gold plated connectors for top performance and decoration. Covers 40 thru 10 without tuner, Add 75/80 with tuner. Add $5 P&H.

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