Slinky Walks Down Stairs and Picks up 80m Band

Originally intended as a way to stabilize sensitive instruments on ships during World War II, the Slinky is quite simply a helical spring with an unusually good sales pitch. But as millions of children have found out since the 1940’s, once you roll your Slinky down the stairs a few times, you’ve basically hit the wall in terms of entertainment value. So what if we told you there was yet another use for this classic toy that was also fun for a girl and a boy?

As it turns out, a cheap expandable metal coil just so happens to make for a pretty good antenna if you hook it up right. [Blake Hughes] recently took on this project and provided some detailed pictures and information for anyone else looking to hook a couple of Slinkies to their radio. [Blake] reports excellent results when paired to his RTL-SDR setup, but of course this will work with whatever kind of gear you might be using at these frequencies.

Before anyone gets out the pitchforks, admittedly this isn’t exactly a new idea. There are a few other write-ups online about people using a Slinky as a cheap antenna, such as this detailed analysis from a few years ago by [Frank Dörenberg]. There’s even rumors that soldiers used a Slinky from back home as a makeshift antenna during the Vietnam War. So this is something of an old school ham trick revived for the new generation of SDR enthusiasts.

Anyway, the setup is pretty simple. You simply solder the RF jack of your choice to two stretched out Slinkies: one to the center of the jack and one to outside. Then run a rope through them and stretch them out in opposite directions. The rope is required because the Slinky isn’t going to be strong enough when expanded to keep from laying on the ground.

One thing to keep in mind with a Slinky antenna is that these things are not exactly rated for outside use. Without some kind of treatment (like a spray on acrylic lacquer) , they’ll quickly corrode and fail. Though a better idea might simply to be to think of this as a temporary antenna that you put away when you’re done with. Thanks to the fact that the Slinky doesn’t get deformed even when stretching it out to maximum length, that’s relatively easy to accomplish.

If you’re looking for a good RTL-SDR to go along with your new Slinky antenna, check out this roundup of some of the options that are on the market as of 2017. You’ll probably need an upconverter to get down to the 80m band, so you might as well build that while you’re at it.

31 thoughts on “Slinky Walks Down Stairs and Picks up 80m Band

    1. I have an end-fed that I ran portable from the Center of Totality in Tennessee during the August 2017 Solar Eclipse QSO Party. It’s manufactured by TN01 Engineering. About $100, but worth it. I made contacts on 20m all over the US, coast to coast and border to Gulf, before and during the ecliipse, with the antenna about 12 feet off the ground between a tree and a portable fliberglass pole on a tripod.

      The antenna has a little canvas pack that it stores in. I keep it in the truck now for emergency comm deployment.

  1. One other classic toy use is to hang one end off a cardboard box or any light resonant surface (hollow door), and hold the other end. Strike with a pencil near the hanging end (gamma drive point) and it makes the classic space ray gun sound. Shields up!

  2. Also makes for a reasonable variable inductor / variable Tesla coil secondary.
    I did have to join a few together though and spray them with lacquer.
    I’m wondering if they make good lenz law trains. I expect quite a lot of current would be required.
    Maybe it could be inverted and make a spring shooter.

      1. I tried to Google loaded dielectric antenna…but most results were way over my head. Can anyone explain to the RF layman the basics like how they work compared with over antenna(s)?

        1. A lot of antennas are designed with the assumption that they’re filled with air. We can “load” an antenna with a higher dielectric than air (eps_r=1) and get interesting properties like bandwidth-widening or impedance matching. But it’s hard to proceed any further without looking at the math. Keep researching!

  3. I’m not very knowledgeable in HF-technology and antenna design but wouldn’t it be possible to build a dipole with a variable resonating frequency or length?
    Just mount one pulley at each fixed endpoint of the installation, loop a rope through these pulleys, tension the rope and connect both ends together so it becomes a closed ‘transport’ loop.
    Now combine this with the mentioned design(s) from the article and attach/knot the endpoints of the two slinkies on the rope near the pulleys. That needs to be done in such a way that if you move/pull the rope in one ‘direction’, both slinky endpoints move to the center and outward again if you pull in the ‘other direction’.
    Now add a motor to one pulley and you can change the ‘length’ of both slinkies from the comfort of your basement or whatever ;)
    Of course this only makes sense if the mechanical distance between the movable endpoints of the dipole is more important than the the actual electrical length of the slinkies…

    TLDR: Replace the rope in the original design with a conveyor belt like construct consisting of two pulleys and a rope.
    Attach the slinky endpoints to the rope so that pulling the rope one way lengthens the dipole and shortens it if the rope is pulled the other way.

  4. If you allow two questions: (1) What metal alloy is used in slinkys? (2) If its’s some sort of steel, why would any HAM radio operator use such a poor and therefore lossy conductor as his antenna when there are better alternatives available for the same price?

    (Or are there aluminium slinkies?)

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