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Here's a portable antenna that you can use for backpacking or camping - not to mention Field Day.

Many hams have discovered the value of using Amateur Radio in conjunction with other hobbies ranging from backpacking to bicycling. Those convenient VHF or UHF hand-held radios are great for short-range communications, but what if you need to talk hundreds or thousands of miles? The answer: HF radios, often QRP style to minimize size and weight. A problem you'll run into as you get set up for portable HFoperation is finding an easily transportable antenna that's efficient enough to let your QRP signal reach out and touch someone.

A simple dipole antenna, usually strung inverted-V style, is hard to beat in terms of efficiency and simplicity. Fan-dipoles work well for two or three hands, but how would you make an easily transportable antenna to cover 80 through 10 meters without creating a tangled mess of wires? Try this 8-Band Backpacker Special! This is what I use on my backpacking adventures; it lets me hop between two bands without even having to get out of my sleeping bag to make adjustments. (See my article, "Operating Backpack Portable," QST, April 1994.)

Table 1 - Eight-band operation can be achieved by extending a 20-meter/40-meter fan dipole. Extensions are clipped to the end of the basic 20- or 40-meter elements.' Carrying an additional pair of 6-inch extensions allows for fine-tuning the antenna.
Band (CW)Basic ElementExtension length(a)Total element(b) lengthAntenna electrical length
80 m40 m32 ft 11 in63 ft 8 in½ λ
40 m40 mnone32 ft 9 in½ λ
30m20m7 ft 2 in24 ft 4 in½ λ
20m20mnone17 ft 2 in½ λ
17m40m7 ft 2 in39 ft 11 in1½ λ
15m40m1 ft 6 in34 ft 3 in1½ λ
12m20m7 ft 2 in and 4 ft 9 in29 ft 1 in1½ λ
10m20m7 ft 2 in and 1 ft 6 in25 ft 10 in1½ λ
  1. Two extensions are required, one for each element.
  2. An element is one-half of a dipole.

Construction

The Backpacker Special consists of a 20-meter/40-meter fan dipole that has extensions clipped to the ends of the elements to make the overall antenna ½ or 1½ wavelengths long on each band. (As used in this article, an element is one-half of a dipole.) Table 1 shows the lengths of the various extensions that need to be added to the basic antenna to make it cover the eight HF bands; each extension has an alligator clip soldered to one end. Several extensions are reused in the various configurations to minimize the amount of wire carried, reducing the weight and bulk of the antenna. (My pack dog, who carries the antenna on backpacking trips, appreciates the fact that the antenna weighs only 1.4 pounds and doesn't take up much space - it leaves more room for dog chow.) The lengths given in Table 1 , typically resonate the antenna on the low edge of the CW bands; for the Novice subband the length of the 40-meter element may need to be shortened about 4 inches, and the 80-meter extension shortened about 18 inches.

Figure 1 illustrates the details of the antenna's construction. I like to use #20 AWG magnet wire for the main elements and #24 AWG for the shorter extensions. The #20 AWG is strong enough to allow it to be pulled down when tangled in tree branches, without breaking the wire. About 32 feet of RG-174 coax is convenient for the feed line. Make sure to strain-relieve the coax at the center insulator. A BNC splice can be inserted close to the center insulator if you want to be able to steal the coax to use with your VHF antenna (a 30-foot length of RG-174 will have about 3 dB loss at 144 MHz).

Fig 1
Figure 1 - Construction details for the 8-Band Backpacker Special antenna. (Shown configured for 30 and 40-meter operation.)

Check the antenna with an SWR meter before you take off on your adventure by setting it up in the backyard or in a park. Install it at whatever apex and element height you think you'll usually use. When I use it, the apex is often supported by a tree branch 15 to 25 feet above the ground and the ends of the elements are 6 to 8 feet high. If you let the ends of the elements get too high, it's hard to reach them to attach the extensions!

Materials

You may be able to use your creativity and junk box to reduce the need to go out and buy everything for this antenna. Few, if any, ham dealers will carry the miniature RG- I74 coax or connectors. RG-58 is fine if you don't mind the extra bulk and weight. The nice thing about the. magnet wire I've specified is that it has a thin film of insulation that will burn off easily during soldering (no need to strip the insulation in advance); but most any type of wire will do. FR-4 PC board material can be identified by viewing the edge of the board and looking for thread-like filaments imbedded inside the material. If you don't have any old FR-4 in your junk box, substitute a high-temperature plastic or some varnished wood (avoid phenolic PC board material because it's too brittle).

If you heed a source for the wire and connectors try your local electronics distributors, or you can order them by telephone from:

Parts list

Hardware stores and Radio Shack have various sizes and styles of alligator clips, tie wraps, and brass eyelets that are useful.

*Crimp connectors can be used without a crimp tool by soldering the collar over the coax braid rather than crimping it on. Take care not to melt the coax center conductor. After it's soldered, place a couple of inches of heat-shrink tubing over the collar and coax jacket for strain relief.

Antenna Tips

WB0KRX, Jim Andera.