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HF Vertical Travel Antenna - Updated:

Phil Salas (AD5X) on December 19, 2002
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HF Vertical Travel Antenna - Updated:
Phil Salas - AD5X

Introduction

I've had a tremendous response to the portable antenna project published in the July 2002 QST. Since this antenna has been so popular, I've continued to improve and simplify it. In the last several months I've evolved the antenna from the original riser design, to a fiberglass design, and now to an aluminum tube design. This new design is lighter and more compact than the original antenna. It is also easier to build, and easier to find parts for.

As before, this new version of the Travel Antenna is designed for easy transport. It breaks down into multiple mast and whip sections, an air-wound center loading coil section, and a small base support with no piece longer than 2-feet so it will easily fit into most suitcases. Yet the fully assembled antenna has a length in excess of 12-feet.

Gathering the parts:

The loading coil, half of a B&W 3027, is available from Surplus Sales of Nebraska (www.surplussales.com). The 3/8" aluminum tubing is found in many hardware stores - or it can be ordered from Texas Towers ($25 min order at: www.texastowers.com). The parts list is as follows:

Three 24" pieces of 3/8" diameter aluminum tubing ($4.20/6' tube from Texas Towers)*
One 3/8" diameter wood dowel ($1.28/36" @ Home Depot - only 5-1/2" needed)
One-half of a B&W 3027 coil ($20 shipped from Surplus Sales of Nebraska)
One 72" telescoping antenna ($4.99 @ Radio Shack 270-1408B/270-1408/27-1408)**
One 3/4 x 3/4 x 1/2" PVC-T ($0.20 @ Home Depot)
One 3/4"-to-1/2" pvc adapter ($0.50 ea @ Home Depot)
One 3/4" PVC Plug ($0.89 ea @ True Value)
One 1/2x1/8-NPT brass adapter ($1.20 @ True Value)
Eight 1/8-NPT brass couplings ($0.95 ea @ Home Depot)
Four 1/8-NPT 0.7" all-thread nipples ($0.75 ea @ Home Depot)
One 1/8-NPT 1" nipple ($1 @ True Value)
One #8 wing-nut ($0.34 @ True Value)
Three #8 x 1" brass screws ($0.08 ea @ True Value)
Three #8 brass nuts ($0.83/6 @ Home Depot)
Three #8 copper-plated steel split lock washers ($0.05 ea @ True Value)
One 3/8x16 x 12" hex head carriage bolt, zinc plated ($1.18 @ Home Depot)
Two 3/8x16 nuts, zinc plated ($0.83/6 @ Home Depot)
One 3/8 lockwasher, zinc plated ($0.83/10 @ Home Depot)
Ten #6 stainless steel 3/8" sheet metal screws ($0.07 ea @ True Value)
Six #6 stainless steel lock-washers ($0.05 ea @ True Value)
One chassis-mount SO-239 coax connector ($1.99 @ Radio Shack - RS278-201)
One #8 spade lug (Home Depot)
72 ft wire (Any gauge, insulated or not, for six 12-foot ground radials)
Six #8 x 1-1/2" brass wood screws ($0.83/6 @ Home Depot)

* True Value and ACE Hardware stores have tubing areas with shorter pieces of aluminum and brass tubing. I found 3/8"OD x 3' aluminum tubes for $2.50 each, and 3/8"OD x 3' brass tubes for $4.50 each. So you can either go with two 3' tubes, or four 1-1/2' tubes if desired. Also, with brass tubes you can solder the couplings directly to the tubes. Make sure you adjust the brass couplings/nipples quantities as needed.

** This Radio Shack part is very confusing. All three of these numbers refer to the proper 6-section 72" whip. It seems to depend on the phase of the moon as to what the Radio Shack catalog, web site, and actual store inventory part has on it.

Aluminum Rod Preparation and Assembly:

See Figure 1 for the assembly details. In order for the couplings to fit over the aluminum tubes, the ends of the couplings that fit over the tubes must be reamed out with a 3/8" drill bit. To do this, first screw a 1/8-NPT coupling on each end of a 0.7" 1/8-NPT nipple. Use pliers and/or wrenches to screw these on tight. Next, grasp one of the couplings with a pair of vice-grips and ream out the opposite coupling with the 3/8" drill bit. Reverse, and ream out the other coupling. Now unscrew the couplings. One end will brake loose, and the other will stay tight in the remaining coupling. You'll now have a female and male end that will fit over each end of the aluminum tubes. You will need four pairs of these male/female brass connectors: three pairs for the aluminum tubes and one pair for the loading coil assembly. If you'd like, you can solder the nipple/coupling assemblies together, however the nipple/coupling assembly tends to be very tightly secured. Finally, drill 9/64" clearance holes into the ends of the three coupling pairs that will slide over the aluminum tubes. These holes will pass the #6x3/8" stainless steel sheet metal screws that will hold the couplings to the aluminum tubes. Please note that the fourth coupling pair is used on the loading coil assembly and will be drilled and tapped for #8 brass machine screws.

Next cut three two-foot sections of the 3/8" aluminum tubes with a hacksaw or tubing cutter. De-burr the tubing, and also slightly file the edges of the tubing to make it easier to push into the brass couplings. As shown in Figure 1, insert the male/female brass pairs just constructed over all three of the aluminum 24" tubes. This could be a tight fit, so you may need to tap the couplings in place with a hammer. Since brass and aluminum are significantly dissimilar metals, you may want to coat the aluminum tube ends with DeoxIt, Noalox or Penetrox to prevent possible corrosion, especially if the antenna will be outside for extended periods of time. To tap the couplings in place, insert the male/female coupling pairs over the 3/8" aluminum tubes as best you can. Then place the nipple-end (male) on a piece of wood, and gently tap the opposite side of the rod (female coupling) with a hammer until the couplings are fully seated. Now, using the 9/64" clearance holes in the couplings as guide holes, drill 7/64" diameter holes through the aluminum tubes, and attach the risers to the aluminum tubes with the #6x3/8" sheet metal screws and lock-washers as shown in Figure 1.

Loading Coil Assembly:

Refer to Figure 2 for the loading coil section. Here, 1/8-NPT male/female coupling pairs are slid over a 3/8" diameter 5-1/2" long wood dowel. You will need to drill and tap a #8 threaded hole through one side of each of the 1/8-NPT brass couplings and into the wooden dowel as shown in Figure 2. Note that the screws are on opposite sides of the rod. Insert the two #8 x 1" brass screws through #8 nuts and lock washers as shown. Tighten the nuts to secure the screws in place. These screws will be used for the coil support.

Now cut off a 5" length (half) of the B&W 3027 coil. Using a screwdriver, indent every other turn of the coil. Position the coil over the screws such that the 1" long brass screw heads extend just above two adjacent turns on each end of the coil. Solder these two turns at each end to the screw heads. On the end of the wood dowel coil form with the brass nipple (male end), solder a 6" piece of insulated wire terminated with an alligator clip.

For extended outdoor use, you may wish to treat the wood dowel with varnish, replace it with a piece of 3/8"D x 5-1/2"L fiberglass rod, or use the riser assembly as shown in the original QST article (July 2002).

Top Whip Preparation:

File the plating off the small mounting stub at the base of the Radio Shack 72" collapsible whip antenna. Once the bare brass is exposed, tin this with solder. Now insert the whip antenna base into the 1/8-NPT x 1" brass nipple such that the antenna base is just below the lip of the nibble. Temporarily hold these pieces together with some masking tape. Now heat the nipple with a soldering iron and solder the brass antenna base to the inside of the nipple. Incidentally, I found that some brass nipples were a little small on the inside to pass the collapsible whip. Nipples I purchased at True Value hardware cleared the whip, and nipples purchased at Home Depot didn't. If you can't find a nipple with a 0.275" ID, you can drill the nipple out with a 9/32" drill bit. Hold the nipple with a hefty pair of vice-grips when you do this and you won't have a problem!

Base Assembly:

In this design, I've used a 3/8x16 x 12" zinc plated hex head carriage bolt instead of the original brass threaded rod. Only about the last 1-1/2" of the carriage bolt is threaded, so it is much easier to clean off the bolt after use. The threaded rod was always a pain to clean. With the carriage bolt, a damp cloth easily cleans it. To prepare the carriage bolt, cut off the hex head and round this end with a file. Referring to Figure 4, drill a 3/8" diameter hole into the 3/4" PVC plug used for the ground support carriage bolt. Cut off about half of the length of the 3/4" PVC plug to leave plenty of room inside the "T" for wiring, insert the carriage bolt threaded end into the plug, and secure with two 3/8x16 nuts and a lock washer as shown. I prefer soldering ground wire to the internal 3/8x16 nut as show. However, this is really not necessary, as the radials will provide the antenna ground - both RF and DC. If you wish, you can PVC-glue the plug in place instead of using the #6 stainless steel sheet metal screws shown. However, the screws make changing the support assemble easy in case you want to have a second support assembly made from threaded rod for mounting onto a trailer mount, metal plate, etc.

Next, place the SO-239 temporarily over the 1/2" hole in the "T" and mark the location for the two #6 x 3/8" long stainless steel machine screws that will hold it in place. You'll see that these holes will be right in the center of the PVC lip. Carefully drill two 1/16" holes at these points. Place the 3/4" PVC plug/spike assembly in the "T" and drill two 1/16" diameter holes through the "T" and plug. Remove this assembly from the "T" and drill out these 1/16" holes in the "T" to 1/8". Also drill out two holes in the SO-239 connector to 1/8" since the holes are not large enough to pass the #6 x 3/8" sheet metal screws.

Next we'll prepare the antenna interface at the top of the base. First, cut off part of the 3/4 x 1/2" PVC adapter so as to leave additional room in the "T" for wiring. Solder a piece of #14 copper house wire directly to the inside lip of the 1/2 x 1/8NPT brass adapter. You'll need a large soldering iron or a torch since the brass adapter mass is pretty large. Screw this adapter tightly into the 3/4 x 1/2" PVC adapter.

Finally, solder wires to the center conductor and to the ground of the SO-239 connector as shown. The wire from the center conductor should be soldered to the wire stub on the 1/2 x 1/8NPT brass adapter at the antenna interface, and then the 3/4 x 1/2" PVC adapter can be PVC-glued into place. I used a short piece of copper braid from a piece of RG-58 cable from the SO-239 ground (soldered directly to the SO-239 body) to the brass ground screw. You can solder the braid directly to the head of the brass ground screw. You can now complete the assembly of the base by inserting the PVC plug/12" carriage bolt assembly into the "T" and installing the #6 stainless steel sheet metal screws as shown in Figure 4. As you can see in Figure 4, I also made provisions for an optional wing-nut assembly in case you need to add capacitive or inductive base matching should you significantly shorten the antenna, or if you have a very good ground-plane and want to improve your VSWR. To make this wing-nut assembly, screw a brass wing-nut tightly against the head of the brass screw and solder these together.

Ground Radial Network:

The radial network is made up six 12-foot radials using #22 insulated wire though any gauge wire, insulated or not, can be used. Attach all the wires together and to a #8 spade lug on one end. This lug will attach to the ground screw on the base assembly. Roll up the six wires individually and hold them together with tie-wraps to minimize the time spent in unraveling the wires. On the outer end of each radial, solder on a 1-1/2" brass wood screw. These screws are pushed into the ground to help hold the radials in place. I put a blob of hot glue on the wire/screw interface to give it a little strain relief.

Antenna Assembly:

To assemble the antenna, first screw two 24" aluminum rods together, and then screw these into the top of the base assembly. Push this base/rod assembly firmly into the ground, keeping it as vertical as possible. Next screw the remaining 24" aluminum rod, the loading coil, and telescoping whip assemblies together. Extend the telescoping whip. Screw this entire top assembly into the female end of the 24" aluminum tube that is available on the assembly currently pushed into the ground. Finger tight is all that is necessary for all brass fitting interconnections. Finally, extend the six radials, and attach the common end to the ground screw on the base assembly.

Antenna Set-up

To find a permanent coil tap for each band, start with 40 meters and use an antenna analyzer to find the coil tap that gives the best VSWR. Mark this tap point. You may want multiple taps on 40 meters so as to cover both the CW and SSB portions of the band. Move to 30 meters and repeat. Repeat again for 20 and 17 meters.

For 15, 12 and 10 meters, the entire coil is shorted. The telescoping whip is adjusted for resonance. Use a permanent black marker pen to indicate the high band positions on the telescoping whip.

Now solder short pieces of wire to the tap points determined for all bands where the coil is used. From this point forward, you can just go back to these tap points, or re-adjust the top whip as necessary, and not have to worry about making VSWR measurements. You'll find that in all cases the VSWR should be under 1.5:1.

Guying and Mounting Options:

This antenna is self-supporting in a no- to low-breeze environment. In many cases it may be necessary to guy the antenna. For effective guying, attach packing twine (3 pieces) around the bottom coil support brass coupler. Extend the twine and attach to tent stakes, nearby shrubs, etc. If you wish to bolt the antenna base directly to a trailer mount or plate, use a 3/8" threaded rod (brass or zinc-plated steel) as discussed earlier instead of the 12" carriage bolt "spike". In this case you should solder the ground wire inside the "T" to the 3/8 x 16 nut as shown to ensure a good ground to whatever the base is mounted to.

Finally, you can easily make a 3/8x24 standard interface so that the antenna can be mounted on a standard 3/8 x 24 ham mount (most antenna mounts require a 3/8x24 stud on the antenna). It turns out that the 1/8-NPT thread is just a slightly tapered 3/8x24 thread. So, purchase a 3/8x24 bolt (your local hardware store again) and screw it tightly into a 1/8-NPT coupling. Cut off the head of the 3/8x24 bolt with a hack saw and file carefully so that the threads are OK for screwing into a 3/8x24 socket. You can now either screw this assembly onto the 1/8-NPT nipple on the bottom fiberglass rod section (See Figure 5), or screw the 3/8x24 bolt directly into the bottom 1/8-NPT coupling as shown in Figure 6 (if you'll never need the 1/8-NPT interface on the bottom antenna section). Now

Conclusion:

Due to the heavy interest in my portable antenna, I've made some changes which makes the antenna lighter, more compact, easier to fabricate, and also gives you more mounting options. You can also experiment with the antenna length - i.e. remove a section or two, use more or fewer sections, decrease or increase sections lengths, or place the loading coil in different positions. And how about 75-80 meters? You bought twice as much coil as you need, so build up a second coil assembly and put both coil assemblies at the base of the antenna. No need to indent or add an alligator clip to this coil. However, there is an efficiency penalty for base-loaded versus center-loaded antennas (but you must use base loading to reach 75-80 meters with this antenna). Also, you will need base capacitive loading to get the VSWR down on 75-80 meters. And finally, don't hesitate to make changes based on hardware availability. Try brass or copper tubing, or even wire wrapped 3/8" fiberglass or wood dowel. Its fun to design antennas "on the fly" while standing in the plumbing section of your hardware store. This makes for interesting discussions with the clerks, however!

Phil Salas - AD5X - can be reached at: ad5x@arrl.net if you have any questions or comments. This is an easy and fun antenna to build, and the total cost should be under $60.

Member Comments:
This article has expired. No more comments may be added.
 
HF Vertical Travel Antenna - Updated:  
by K6SBA on December 20, 2002 Mail this to a friend!
This antenna is highly recommended. I have built several versions of Phil's antenna using a variety of materials. All play great. At 12 feet, this antenna is approaching a 1/4 wave on 20-m, yet it can be broken down into a highly transportable package. If you have one of the new hi-tech QRP rigs (FT-817, K2, etc), this is the ideal companion. With a few counterpoise wires thrown around, this antenna will definitely outperform all the commercial "shorty" antennas that are currently available.

73 de K6SBA
David in Santa Barbara, CA
 
HF Vertical Travel Antenna - Updated:  
by N2YTF on December 20, 2002 Mail this to a friend!
Phil, thanks for your great antenna designs!
Folks, get out there and build this antenna...it will really enhance your field operations.

I built Phil's HF travel antenna as it appeared in QST and it really gets out. It has even allowed me to work my first 6m outside of the states (New York City to Canada with the antenna in my backyard...a lousy radio location).

One question for you, is the "on the air" preformance of the new design better than the one portrayed in the QST article?

I cant say enough good things about Phil's antenna, and I brought it checked it on several planes this summer with no security problems (although it did look like someone opened the bag to have a look....personally I like tight security), despite tight secutiry being in place.

Oh one more thing, those "sprinkler system risers" mentioned in the QST article were very difficult to find in New York City.....most hardware people didnt have any idea what they were (I certainly didnt know what they were)...even the folks at Home Depot didnt have a clue. I eventually found a Home Depot out on Long Island that stocked them. I guess this is not a problem with the new design.

73 and thanks again
Thomas, N2YTF
 
RE: HF Vertical Travel Antenna - Updated:  
by AD5X on December 20, 2002 Mail this to a friend!
Thomas - The "on the air" performance will be negligibly better with this design, due to the small decreases in losses (this design uses aluminum tubes vs the old design with wire on plastic risers). I suspect no one would be able to tell the difference.

Phil - AD5X
 
RE: HF Vertical Travel Antenna - Updated:  
by KL7IPV on December 21, 2002 Mail this to a friend!
Phil,
I had just bought a similar B&W coil on e-Bay and using a RS 72" telescoping antenna, made a similar antenna. I used the MFJ 259 analyzer to mark the places on the coil for each band. I finished it a day before the QST arrived in the mail with your story. I used some heavy plastic stock that I had but yours certainly would have been easier to do. I used a Hustler short antenna mast for the base which allowed me to use a mag mount for the antenna. Most of us can't build radios to compete with the big guys but antennas are always open for experimentation. I wonder if the proliferation of QRP rigs is helping push the antenna developement that seems to be going on now?
73
Frank
KL7IPV
 
HF Vertical Travel Antenna - Update - 3/8" Al  
by N6KD on December 26, 2002 Mail this to a friend!
Since my local store had 3/8" Aluminum Rod and no 3/8" tubing - I substitued and eliminated many of the required couplers by threading one end of the 3/8" rod. The antenna is slightly heavier - but less expensive to build. Great little antenna.
 
HF Vertical Travel Antenna - Updated:  
by WA1GJF on January 27, 2003 Mail this to a friend!
This is one neat, easy to build portable antenna. As a matter of fact, I now use it as my primary antenna at home, and am having remarkable results running 1/2-5watts. Phil has been terrific in responding to my e-mails, answering my questions and offering additional advice.
Ground mounted, 6 radials thrown on the ground, and I am heard better than my attic dipole.You really have to build it and find out for yourself that this is a terrific antenna!
 
RE: HF Vertical Travel Antenna - Update - 3/8"  
by KF0UR on April 14, 2004 Mail this to a friend!
I, too, used 3/8" aluminum rod and threaded the ends. Although I could not get all the rods threaded as straight as I'd like, it worked great...mechanically and electrically. I cut the pieces into approx. 14" lengths to match the length of the RS whip, which makes it a little easier to put in a backpack. You wind up with 5 rods instead of 3.

At the bottom of the PVC tee, I used a ring of stiff wire (a loop of a coil) that goes around the PVC that each radial clips to.

Total weight, including 1 foot stake, radials and 25 ft of RG-58 is 3.5 lbs.

Using six 12 foot radials, it performed very well (first QSO was with an HK running 5 watts on 20M PSK31. Using on-air tests, it compares very favorably with a dipole that I been using successfully for years.

 
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