What is a Slinky Dipole Antenna?

What is a Slinky Dipole Antenna?

Many of you would have seen children play with Slinky toys which are spring like as illustrated in the picture. Slinky Dipole Antenna uses helical springs to have it shortened so that some have mounted it in attic when there was no way of having an external antenna. N1FDX used a Slinky dipole with a 1:1 balun and a remote antenna tuner located at the antenna. He could remotely control the tuner from his radio sitting in his shack. He had used the antenna in different configurations including horizontal dipole, vertical dipole and as small as 5 feet per side. He could tune it from 80 m to 6 m and even 160 m! He could make numerous contacts through out United States as well as west coast of Europe on 20 and 40 m.

100 Watts would be the typical maximum power which can be used in such locations as higher power could heat up the surrounding nearby structures and cause damage to them. One recommendation is that the antenna may be no more than a quarter wavelength and could be much shorter. Instead of using an antenna tuner, the Slinky Dipole Antenna can be tuned by shorting out a few coil windings with alumninum clips. People have passed a nylon rope through it to support it in horizontal position. A commercial Slinky antenna coil has 67 feet of spring and is very short when compressed.

Diameter of the coil is small compared to the wavelength and the length of the coil. Typically it can be stretched into a helix as long as 15 feet without becoming deformed. The original US patent granted in 1974 was as a tunable spiral dipole antenna. The patent for the tunable spiral dipole antenna expired in 1991. A coaxial cable can be used as the feeder while using the Slinky dipole as a resonant monoband antenna, usually on 40 m. If it is being used as a multi-band non resonant antenna, twin-lead or ladder line is used along with a tuner.