It Began Without a Tree: My Search for a Walking Stick Antenna
The ARS Sojourner
I've long wished for a light, effective, easily carried and quickly erected antenna to use on the treeless trails I love. I decided to make a "walking stick" vertical for 40 meters for my winter pictoglyph hunting trips.
Ideally, I'd like an antenna I can just poke in the dirt and use. A vertical should be ideal, because the radiation pattern is doughnut shaped, with a low takeoff angle. Tall vertical antennas with lots of radials are blockbusters for DX, and shortening the antenna and removing radials doesn't change the theoretical pattern very much.
That sounds good, but ground and coil losses quickly eat the radiated signal if a vertical is compromised. I've tried using "Ham Stick" and other short mobile antennas as radiators for this application and found them unsatisfactory.
A successful walking stick vertical for QRP use must be exceptionally efficient. Radials are a must, a high-Q coil should used, and the radiator should be as tall as possible.
A sturdy 20 foot telescoping fishing pole became the basis of my walking stick antenna. I found some thick rubber chair leg covers at the local hardware store that look like crutch tips. They keep dust and dirt out of the telescoping fiberglass elements and allow the pole to actually be used as a walking stick.
The radiator is about 18 feet of insulated 22 gauge wire. I thought of making it about 16 feet to double as a quarter wave antenna on 20 meters, but hoped that a longer radiator would increase the efficiency. I attached a "Bic" pen cap to the top of the wire with heat shrink tubing so I can quickly slip it over the tip of the fishing pole.
I wanted the biggest loading coil I could carry easily. Bigger wire and a large diameter increase the Q and reduce coil loss. I wound some coils and found them satisfactory, but ended up using a piece of B&W miniductor left over from an ancient project. The plastic struts were crumbling, so I reinforced them with epoxy. If you can find it, tiny copper tubing makes great coil wire. It's easy to wind and retains its shape.
Epoxy paste holds the coil in shape like a champ.
My coil mount is made from a few inches of PVC pipe. A vertical slice of pipe fits snugly against the mast, and a round segment provides a place to attach feedline and radials. I hooked the coil to the mount with epoxy paste.
After some experimentation, I found that rubber O-rings provide a wonderfully cheap and powerful way to attach the coil mount to the mast. An old plastic medicine jar provides protection for the coil while it waits in my backpack. I set up the antenna (including the radiator and radials) and found the resonate length of coil at 7040 KHz using a grid dip meter.
I then found the 50 ohm feed point by moving a tap until the SWR dropped to 1:1.
My coil is roughly 2.5 inches in diameter and 1.5 inches long. It has 17 turns, and is fed about one turn "up" from ground. The adjustments are touchy, but once set up the SWR is 2:1 or less over 60 KHz of the 40 meter CW band.
I placed the coil near the base of the mast at a convenient location. The mast is strongest and the coil easiest to reach there. No capacitive "hat" is required, and a coil at the base requires fewer turns than one placed nearer the middle or top of the radiator.
It was fun to experiment with radials. Resonant lengths of wire are not important with this type of antenna, but the radials should be as long as convenient. Mine are about 16 feet long, left over from some old antenna experiments.
I calculated that doubling the number of radials should give roughly .5 db gain by reducing ground losses. I can hear the difference between one and four radials on received signals. I tried 8 and 16 radials, but they were a lot of trouble to set up, and I couldn't perceive the difference.
Placing radials is the most awkward, time consuming and frustrating part of erecting the antenna, so I decided to be content with four. I use banana plugs to attach the radials to the coil mount.
The size of the wire does not influence performance. Some 24 gauge Teflon coated wire is great for this application because it doesn't kink or twist when it's wound up for storage.
I'm still having trouble finding a really good way to hold the pole upright. I carry a lightweight spike which I drive in the ground with a rock.
O-rings hold the mast to the spike reasonably well, but I've also been taping it for security.
The completed antenna weighs about two pounds and is easy to carry. I can set it up in about 5 minutes.
It has been used on three trips so far this winter, and it seems to work well.
I've included a few pictures of a mid-January pictoglyph hike that show the antenna in action.
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Dr. Bob Armstrong, N7XJ, a contributing editor to The ARS Sojourner, is an expert QRPer, builder, experimenter and outdoorsman living in Mati, UT.