L>SlinkySlinkyClandestine DipoleSlinking 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 aSlinky is compressed it is only 2-1/4 inch long, but it can be stretched into a helix as long as 15feet in length without deforming. An antenna made from a Slinky is light, simple to suspend andextend, 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 mechanicalproperties. But it turns out that the Slinky has some interesting electrical properties at radiofrequencies too. Since it is a helix made of conducting material, it will be self resonant at somefrequency. In fact, a standard Slinky coil resonates as a quarter wave between 7 and 8 MHzwhen it is stretched to lengths between 5 and 15 feet. To tune the Slinky within that range onemust only extend the coil to approximate size, then expand or contract it to reach the desiredresonance. At a length close to 7-1/2 feet a standard Slinky is quarter-wave resonant on 40meters. 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 abovethe 7-8 MHz range may be created by removing turns to shorten the helices or by shorting outturns. A twenty meter dipole, for example, can be made by cutting a Slinky coil in half or simplyby feeding it with a delta match in the center.For target frequencies below 40 meters, oneadds turns from another Slinky coil or clips wire pig tails on the ends. For example, by addingone more coil to each side and stretching the whole to about 30 feet in length, you can make an80 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 30foot 80 meter Slinky dipole at 20 ft received signal reports on average 1-1/2 S-units lower than aTNT Windom at 35 feet. That"s not bad for a 1/10 wavelength antenna. It would have donebetter 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, slinkingaround 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 toobtain multiband results with a pair of Slinkys is to stretch them as far as space permits and clipon 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 bands7 MHz and above and in a pinch it will permit QSOs on the 80 meter band.2. Note that thecoils will corrode if left outdoors for more than a few weeks. Corrosion will take place on thesurface where the RF energy wants to travel. This means that the Slinky is really best suited toindoor or portable deployment. If you wish to put your Slinky antenna outside on a more or lesspermanent basis, you should solder all connections well, then paint the whole antenna with sprayenamel.3. Slinky coils are not self supporting so you need to use a messenger line to supportthe weight of the coils.4. For a given Slinky antenna, performance seems best at thefrequency of natural resonance and on the next harmonic because the coils act increasingly likean RF choke on the higher harmonics.Have Fun Slinking AroundKidsdon"t know half the fun of a Slinky. Could they imagine talking into one and having someonefrom Japan answer them on 15 meters? Or think of checking into MARS and RACES nets with aslinky on the bedroom wall? Only in amateur radio can you get a bang like this out of aslinkyAntennasWest has put together what you need to get off to a fast start with your slinkyexperimentation. Check out the items listed below and turn a weekend with a slinky into themost fun you"ve had since you were a kid . Slinky Antenna ProductsTechNote 123D $7 ppd.This frequently updated Technote reviews slinkyexperiments performed todate. Gives detailed information on the electrical properties ofSlinky coil antennas. Describes instruments used & designs tested. Reportsunpublished experiences of numerous contributors.Shows how to get the most out of aslinky with or without an antenna tuner. Reviewswhat works and what doesn"t.SlinkyExperimenter Pack $13 Here"s what you need to get started-a pair ofslinky coils, a quick & easy center support, and the latest edition of Technote 123. Runyour own experiments. Add $5 P & H.QRV Slinky Antenna $35This is the fully refined and ready to use QRV Slinky system, all set to go for instantmotel, attic, or portable useSilver tipped coaxial feedlineis decorator white.Quick attachmentclips make it a snap to hook up fast.Slick transparent support line lets antenna slide in and out of action instantaneously. Uniquedesign 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 andgold plated connectors for top performance and decoration.
You are watching: How long is a slinky stretched out
See more: What Is The Molar Mass Of C3H8? ? Molar Mass Of C3H8
Covers 40 thru 10 without tuner, Add 75/80 with tuner. Add $5 P&H.Back To Home