"Editor's Note: Due to the popularity of some of eHam's older articles, many of which you may not have read, the eHam.net team has decided to rerun some of the best articles that we have received since eHam's inception. These articles will be reprinted to add to the quality of eHam's content and in a show of appreciation to the authors of these articles." This article was originally published on: 06/03/2003

Re-Inventing the Tape Dipole

About 20 years ago I traveled with a Heathkit HW-8 and a Hy-Gain TD-1 tape dipole in my bag, and both saw quite a few exotic locales. The QRP transceiver by now is an Elecraft K1, and like the HW-8 the tape dipole was sold somewhere along the way. I normally use a MP-1 vertical for my portable operations, but often, when I have space for a full-size dipole, I wished that I still had the TD-1. (which also was available in a military version from Rockwell-Collins called, I believe, the HD-4000) I've tried a few modern light-weight incarnations of the reel dipole, and although they work fine none of them had the sturdy reassuring feel of the old TD-1.

 

When I spotted these chrome clad 50' measuring tapes on eBay, the pair for $13, somehow they just cried out to be made into a tape dipole. The cases are made of metal coated with plastic and quite rugged. It turns out, although the tape looks like shiny bare metal, it is coated with some stuff that is an excellent insulator - so you have to use steel wool to remove it in some spots - but more about that later.

 

An aluminum U-profile, 3/4" wide and 1/2" high, normally used to protect the edge of plywood, looked like a good choice for a frame to hold the reels. With a bit of handiwork with a metal saw I fashioned the two brackets that hold the tapes. They are bolted together with a 4 1/2" bolt with nylon spacers in between. (all the materials I used are readily available in hardware stores).

 

The old TD-1 had a screw-down clamp to stop the tape, which also served as the electrical connection to the tape, and the dust and dirt that gathered in that spot rubbed off the markings on the tapes pretty quickly. So it's probably not a disadvantage that these reels have nothing of the sort. I chose to make the actual electrical connection using binder clips that squeeze a short length of grounding strap firmly onto the tape. Since the tape is coated you have to use steel wool to remove the coating over some length around the desired point of contact, and it turns out that this works quite well.

 

The finished product is definitely not designed for the backpacker, but it conveys the heft and sturdiness that I remember from the TD-1. With its aluminum frame it is probably even more solid than the original. Taking a clue from the original I have attached a laminated frequency-to-length conversion chart to the back. Unlike the TD-1 with its 66' reels the two 50' reels will not permit operation on 80m. However, since I'm rarely ever on 80m and my K1 is not configured for it, that's not something I miss. I believe that similar tapes are available in 100' length, so you could construct this antenna to cover 80m, too. The whole thing looks and feels professional and solid, which was my most important objective.

 

My construction has a SO-239 connector that directly connects to the antenna without a balun. I felt that an electrically balanced situation is probably not going to occur in the odd locations that this antenna will be used in, and therefore the added complexity of a balun didn't seem justified - the TD-1 didn't have one either. (Although a small balun can easily be added to the construction.)

How does it perform? That's, of course, hard to say since I can't switch to another antenna easily. Stainless steels tapes are not a particularly good material for antennas if you're looking for low resistance material - but then, real wire antennas out there gather a coat of oxidation pretty quickly which introduces some resistive loss, too. Over all the antenna seems to perform quite well - I get into Europe and South America on 20m with 5W quite regularly from the East Coast despite the lackluster conditions. Setup is very simple using the length chart, and my Elecraft K1 has no problems giving me a 1:1 SWR every time. For a total cost of about $25 and a few bruises on my fingers from the metal work I have an antenna that is at least as rugged as the TD-1 and should travel with me for a long time to come. (and this time I'm not going to sell it unless you make me an offer that I can't refuse ...)