By Shel Radin KFØUR
Years ago when I started operating QRP portable, I was in search of the “right” antenna.
But let me first describe my definition of QRP Portable, as it can mean so many things. In my case, it is hiking with a small backpack for the day on the Colorado Rocky Mountain trails near my QTH in Colorado Springs. I’ll hike for an hour or so, find a place with a beautiful view (required!), set up quickly and operate for a number of hours.
My antenna requirements were relatively simple (at least in my mind). They included:
- Cover 10-40 meters
- Be easy to set up and tear down…especially tear down as I usually wait too long to clear out when thunderstorms are approaching and need to make a fast exit.
- Be lightweight and easy to carry, so I can keep the overall backpack weight down, and have room for another bottle of water and peanut butter and jelly sandwich.
An internet search led me to a plethora of possibilities, but the one that caught my eye was a design by Phil Salas, AD5X. Actually after Phil’s original design was published, there were a number of variants found.
It was basically a 12 foot tall vertical, center loaded (coil in the middle), and some radials on the ground. I liked the simplicity of it.
As I recall, the original design used plastic sprinkler risers as the vertical part, as they just screw together. Wires were run up their sides to make the radiating part of the antenna. Other variants used metal rods screwed or clamped together, instead of plastic risers.
So I built one of the metal rod versions. It worked, but I didn’t like the number of pieces involved. It didn’t fit my requirement of easy set up. And there were pieces that could be dropped and lost. I’ve witnessed too many times that a dropped screw or clip seems to get absorbed by the earth, never to be seen again.
Fast forward a bunch of outings and I came up with a solution that met all of my criteria, and by the way, works very well. I think I built 4 versions before I settled on this one.
It’s still a 12 foot antenna, center loaded…but it’s built with fewer components.
The bottom 66” is a heavy duty telescoping whip from BuddiPole. It has a 3/8 x 24 thread on the bottom, which is very handy.
The top 6 feet is a light duty telescoping whip, the kind you used to find at Radio Shack for $6. I don’t think they sell them any longer, but should be available elsewhere. At the time of this writing, Buddipole sells one similar with a ¼” x 20 threaded bottom.
The coil in the center is a 2 inch diameter coil, 10 turns per inch. I used a coil length of 5”, but this could be shorter as I’ve never used all of it on any band.
To hold the whole thing up, I used a PVC tee from the local home improvement store (Home Depot in my case). This sits on a 12” rod that you bang into the ground using a nearby rock, or instead Velcro to small bush or branch. I always have some Velcro with me.
Let’s take a look at the details of how it’s put together.
The first thing to know is that there is nothing critical with any of these parts. This is what I found at the store when I went looking. Feel free to substitute just about anything, including the size of the coil.
There are only a few things to build. Here’s a quick overview:
There’s a base made from a ¾” PVC Tee. Figure 1 shows it put together. Figure 2 shows it piece by piece. The 66” BuddiPole whip screws into the top into the brass fitting. It already has the correct 3/8” x 24 threads.
The components of the base, shown in Figure 2 are as follows:
Here’s the center coil which is supported by a small dowel and some brass tubing.
1. Solder leads to an RF connector. It can be an SO-239 or BNC. I use a BNC because my LMR-100 or RG-174 coax has BNC connectors on it.
2. Mount the RF connector on the PVC Plug. You can solder the leads after you mount it, but I found it easier to get the leads on first.
3. Insert the Plug into the side of the PVC Tee. If it’s a smooth plug (not threaded), put a drop of PVC cement on it to hold it in place. Not much is needed. Note: every time I look, the design of these plugs change. Remember…nothing is critical in the design.
4. Solder the lead connected to the center of the RF connector to the brass fitting. I just used a 100 watt soldering gun and soldered it to the end of the brass fitting.
5. Screw the brass fitting into the PVC adapter.
6. Solder the lead connected to the ground of the RF connector to a lug.
7. Make a ground ring as shown and connected it to the ground lead from the connector.
8. Slide the ¾” to ½” PVC bushing into the bottom of the PVC Tee. Use a drop of PVC cement to hold it in place. This bushing has ½” threads on the inside.
9. Screw the 4” x ½” nipple into the bushing at the bottom.
10. Drill a hole in the end cap that screws on the bushing. This is so it fits over the support rod that you bang into the ground and holds up the vertical. The rod I used is 3/8” threaded, so I drilled a 3/8” hole.
11. Screw the end cap with the hole onto the end of the 4” x ½” nipple.
1. Cut a ¼” dowel 5” long.
2. Cut two 2¼ “ pieces of 9/32” hollow brass tubing. This tubing fits over the end of the Buddipole whip snuggly. And the 6 foot light duty whip fits inside the tubing nicely. I found the tubing at a local hardware store (not a home improvement center). If you use something a bit bigger, you can always put a few dimples in it to make it more snug.
4. Place a brass piece onto each end of the dowel, so that the dowel is about halfway into each brass piece. Glue or epoxy it in place. In the end, you have a dowel with brass tubing on each end and the overall length, tip-to-tip is approx.. 8 ¼”.
5. Solder a 6”-7” lead onto one of the brass tubes. This will be the bottom of the coil assembly. I used small ground braid for its flexibility.
6. Put some kind of clip on the end of the lead (mini-gator, easy-hook, etc.). This will clip onto the coil to short out turns as needed for each band.
7. (optional) take a screwdriver and push in every other turn on the coil. This just gives you more room for the clip.
8. The coil I used is 5” long, 2” wide, and 10 turns per inch. Unravel about 1.5 inches of lead from the coil from each end. Place the dowel and brass assembly in the center of the coil and solder each unraveled end of the coil to the brass tubes. Now the dowel is in the center if the coil, and is supporting the coil as each end is soldered to the brass tubing.
Cut some radials. There are as many articles on radial length and number as there are types of wire. I used six 12’ radials because I read someone else used them with success. Six radials are a manageable number and fits the requirement of easy set up and tear down. I chose bright yellow so they are easily seen and a jacket that does not kink (it might be Teflon). But feel free to experiment.
Put a clip (alligator, mini-gator, easyhook, etc.) one end. When deploying them, simply clip them to the ground ring on the PVC base.
Get a rod to stick in the ground. I use a 12” x 3/8” threaded rod, with one end ground to a point, to make it easier to bang into the ground.
Putting it up on site
1. Bang the 12” rod into the ground. A nearby rock makes a great hammer. Leave about 4” sticking up out of the ground. Or sometimes I just Velcro it to a small bush.
2. Thread the 4” x ½” PVC nipple with the end cap onto the bottom of the PVC base. Place the PVC Tee assembly, nipple first, over the rod.
3. Screw the 66” BuddiPole whip into the brass fitting on the top of the PVC base.
4. Slip the brass tube on the bottom of the coil on to the top of the BuddiPole 66” whip.
5. Slip the 6’ light duty whip into the brass tube on top of the coil assembly.
6. Clip the shorting lead on the coil to the approx. position for the band you are going to work.
7. Extend both whips fully.
8. Lay out the radials and clip them to the ground ring on the base.
9. Attach the coax.
10. Tune the antenna by moving the shorting lead on the coil as needed. Some experimentation is required to find the right spots. Once found for each band, I marked them with my XYL’s fingernail polish. This will change somewhat as you move locations and the ground conditions change, but it’ll get you close every time.
That’s it. There’s not much to it, and nothing very technical. Feel free to experiment with other construction ideas. Note that when the antenna is up, it’s not absolutely vertical. This is OK.