I used to work for Jon Titus, KZ1G, when he was editor of Test&Measurement World magazine. In addition to being a fine editor, he is the developer of the Mark-8 Minicomputer, which some folks consider to be the first personal computer. He published an article on how to build this computer in the July 1974 issue of Radio-Electronics.
In addition to being a personal computer pioneer, he’s also been a ham radio operator for a long time. At one point, he acquired the patent from the inventor of the Slinky antenna and sold them for a number of years. The patent has since expired, but he still owns the trademark.
I found out about this one day while we were talking about antennas. He was so enthusiastic about the antenna, I said that I’d have to try it for myself. He said that even though he no longer sold the antenna, he thought he still had some of the parts, and that he’d look for them when he got home. A couple weeks later, a package arrived containing two Slinkies, a center insulator, two aluminum clips, and an instruction sheet.
The Slinky dipole antenna, for those unfamiliar with it, uses two Slinky coils instead of wire for the dipole elements. The Slinkies used for the antenna have a bigger diameter than the Slinky toys. This allows you to use fewer turns than if you used the Slinky toys for your antenna. Jon had these coils specially made.
When stretched, the Slinkies form are helical coils. To keep the coils horizontal, you must string a rope through the Slinkies and attach the rope to the antenna suports. I use a pulley attached to my house as one antenna support and a tree branch for the other.
The length of a dipole made with Slinkies as the elements is much shorter than a dipole made simply of wire. In fact, the instructions recommmend that the overall length of the antenna be no more than a quarter wavelength and can be much shorter. You tune the antenna by shorting out a number of coil windings with the aluminum clips.
A Long Time Coming
I hate to admit this, but it took me years to actually build the antenna. What finally prompted me to do so was that our club set up a multi-op station to work the Michigan QSO Party. I figured that the Slinky would be easy to set up and tune, and beause it’s a short dipole, could fit in a small space if need be.
As it turned out, it was all of that. At first, we decided not to use the antenna. Our host had erected an 80m bazooka antenna, and one of the other guys had brought a multi-band trap dipole. Because we only planned to operate two transmitters, we figured that we’d use a tuner to load up the bazooka on 40m, and use the trap dipole on the higher bands.
As it turned out, however, we weren’t able to get a good match on 40. So, we scrambled and put up the Slinky, tuning it to 40m.
At first, we thought there was something wrong with the antenna. While Tom and I struggled to erect the thing, Sam was reading the SWR with my antenna analyzer. At one point, Sam said, “The SWR looks pretty good now,but it’s jumping around.” I asked myself what could be wrong– bad solder joints, bad coax?
I went downstairs to see for myself. The measurements were indeed jumping around, but as I puzzled over this, I soon noticed that the SWR jumped whenever the operator of station #1 began sending. What we were reading was not a high SWR, but rather RF being emitted by the first transmitter!
After solving that little teaser, we hooked it up to the Drake Twins we were using on 40, and it worked solidly, if not spectacularly for the rest of the day. When we decided to pack it in, it took us only 15 minutes to take it down.
Last weekend, I strung it between two trees in my front yard so that a friend and I could work two transmitters in the Fists Spring Sprint. Despite being only 15 feet off the ground, it worked well despite poor band conditions.
The next day, I took it down and put it up in my backyard, tuning it to 30m instead of 40m. I’m working almost everything I can hear, and getting good signal reports in the process.
One thing I notice about the antenna is that it doesn’t like being wet. The SWR goes from about 1.1:1 to almost 1.4:1 when it rains. Maybe that has something to do with the supporting rope.
Despite it working so well on 30, I think I’m going to put it back on 40. There just isn’t enough activity on 30 for my taste. More about 30m later.
Links
Here are some links describing the Slinky Antenna and variations on the theme:
Am bidding on one right now through eBay. Will report if I “win” and get it working. Thanks for the general background and operating report.
Tom
N3VUF
I am so fascinated that after all of these years that a thought of “The Slinky Depole Antenna” is actually still “out there”….I first heard of it back in the 80’s. I believe John had a brother named Christopher who also was affiliated with The Blacksburg Book Co. who worked out of a small home in Northen Presque Isle, Maine. I worked for Chris with mailings and I believe it was John with whom I sent his belongings to after Christopher passed away due to an automobile accident.
Anyways…it is good to see that someone kept going with an idea that was explained to me all those years ago.
I built a Slinky antenna using a 1-3/4-in. diameter Slinky found in novelty stores. I used a “cross frame made from 3/4-in. PVC pipe. Each horizontal arm was 10-ft. long.
The arms were glued into opposite sides of a four-way tell. Glue a 2-ft. piece vertically in the tee. From the top of that vertical section, glue a cap with an eyebolt in it to tie two cords to support the horizontal arms. These cords should be about 10-ft., 2-3/8-in. long. (Use 11-ft. lengths for adjustment.) After the 10-ft. sections are completed, slide the Slinky of them. Then, on each end of the horizontal pieces, glue a cap with an eyebolt for the support cord and the end of the Slinky.
When the assembly is complete, fasten the cord from the top eyebolt to the arm eyebolt and adjust for a horizontal position. Then, secure the cords. I used a 4:1 balun to connect the two Slinkies to the coax/tuner. It works lots of bands and you can adjust the Slinky lengths for the best match.
GL & 73,
Rich
Hey, Rich. Thanks for your comment. Do you have a photo of your antenna. If so, I’ll post it along with your comment….73, Dan
1
Hi Dan, I have red everything that I can about slinkies. I have 2 questions:
1. How much rf power can you run through a slinky?
100 watts?
125 watts?
More than that?
I know you used it in the Michigan QSO Party, so it must be able to work with at least that much power, or more, right?
2. When we put it outside, one article says spray it with clear spray paint. I have a can of spray paint, and I have a can of primar. I am blind, so, I have no idea what color the spray paint is.
I have never done this spray paint kind of thing before. I don’t know if the spray paint is clear, or, if it is a certain color.
I would think, to keep the rust off the slinky, and keep it like new, we should put the spray paint on first, then, the primar, is that right?
They say there is no such thing as a dum question, so, I’m asking these 2. So, if you could email me back with the answers, I would appreciate it, please.
73,
Trippy, ac8s
Most Slinky antennas that I’ve seen can handle 100 W no problem.
I did not spray my Slinky, and it did get rusty, so I think painting it is probably a good thing to do. I’m not a painting expert, but generally, you put primer on first. I just did a little Googling and see that Rustoleum has a paint specifically for galvanized metal. Maybe that’s what you want to paint it with.
Hi all,
I do have another question about the slinky. I know that you do not stretch out the slinky more than 15 feet, because stretching it out any further will deform the slinky, and make it unusable for an antenna. The question is, when spray painting it, I would think that I should not paint any more than 15 feet of the slinky? Is that true?
Looking forward to getting an answer on this question, because I sure don’t want to make the slinky unusable for rf to go through.
Trippy
I’ve never heard about this 15-ft. rule. I suppose that stretching the Slinky too much will make it more difficult to short windings when tuning it for other bands. Actually, I hadn’t thought about needing to short out windings when talking about painting before. I suppose that the paint should be conductive to allow the windings to short to one another.
Hi Dan,
You mentioned using the slinky in the Michigan QSO Party. How far did you stretch out each slinky? Also, you mentioned using the slinky for spring sprint, and stretching it between 2 trees, how far did you stretch it then? Also, you mentioned using it at your house, how far did you stretch each slinky out then?
I ask these 3 questions, because at least then I’ll know how far you can stretch it out, and still use it. You mentioned it worked on all 3 occasions, which is fantastic!
Trippy
The Slinky antenna that I used stretched between my house and a tree out in the backyard. That tree unfortunately died, and I had to cut it down, but I’d guess that the total length of the antenna was between 25 and 30 feet.
Hi Dan,
Thanks for the info! So, you were in the 15 feet rule, a total of 30 feet, 15 on each side. Here’s one place where you can find out about that 15 foot rule. It’s in the product description of the slinky antenna, found at
http://www.eham.net/reviews/detail/7374
Trippy
https://www.youtube.com/watch?v=6w2TaQlyqiE
PORTABLE, ROTATABLE, 10 – 80 SLINKY DIPOLE. USES 2 @ 67FT SLINKYS [WHEN EXTENDED] STRETCHED OVE 2 – 10 FT SECTIONS OF 3/4IN PVC PIPE. I USED SEVERAL TURNS FOR CONNECTIONS. THIS IS F.D. 2017. HAVE STILL PICS SHOWING MORE DETAIL.
FWIW my Slinky dipole is, as I write this, over my head in a second floor shack, stretched about 16 feet. I use it for 6 meters. Attached to either my IC-703+ or FT-817ND I’ve made several SSB and CW contacts out towards the east coast during openings. 4 years ago I heard a 6 meter opening and blindly hooked up the Yaesu through a Z-11 Pro and made the first and second 6 meter contacts ever. My Icom will only match it on 40 and 6, making me think that SWR in those bands must be “better” than the others. Thanks for the article here. 73
Doc WB0FDJ
A little late to the thread, but…. my Slinky antenna consists of 2 Slinky’s (65′ of wire each) mated together with magnet wire, then soldered. I then attached it to the top of a 33′ MFJ mast, and it naturally hangs down to about 30′ when the mast is fully extended. I pull it down a bit more and attach a piece of para-cord to the end of it to keep it from wanting to spring up and down. For the connection I made a 1′ piece of coax with a PL-259 on one end, and alligator clips on the other. Clip the center to the Slinky, and clip the shield to a stud on the drive-on base I use to support the mast. Counterpoise wires are also attached to the stud. The coax adapter then connects to a 9:1 unun, then on to the tuner. I can get a usable match with the LDG Z-817 on 80 through 10.
It works as well as any other vertical I have, with one exception…… this thing has HUGE ears! The difference in receiving between this, my usual dipole, and a Wolf River Coils SOTA Special is night and day. Sunday morning up at 9000′ elevation, I could barely hear a station in Japan on the WRC vertical, but as soon as I switched to the Slinky he was S9. I was running QRP and could not get through the pileups though. But I have made contacts on 6 watts to all four corners of the USA on it. Quite simply, it works. It hears extremely well. And makes for a lot of “wait, what did you say you are using for an antenna!?!?!” comments!
Living in an HOA, it doesn’t get set up at home very often. But I enjoy going up to the mountains on the weekends in the early morning where there is zero QRN, and it always gets set up then, unless it’s very windy. I would be glad to send pictures if you would like.