Home--brew buddipole-style

Portable Antenna system

 

An alternative design and construction method

for the BUddipole-style configurable portable antenna system

From the first moment I read about the Buddipole antenna system, I knew two things. 

First, I thought it was a great idea, and I wanted one. Its portability and flexibility seemed like a perfect match for my
Elecraft K3, which is designed for portable use. I also was fascinated by the fact that the Buddipole is a complete system of components capable of being assembled into multiple antenna configurations that function on every ham band from 40 meters through 2 meters. 

Second, as an inveterate home-brewer, I knew that I wanted  to make my own. I decided to start with a clean slate in terms of materials and form factors, with a result that although my antenna system is electrically similar to the Buddipole, it is physically quite different. The “tee” is made of a “sandwich” of aluminum and plastic; the “whips” are constructed of segments of 3/8” hollow aluminum tubing. The mast is made of 1” aluminum tubing, and mounts in a pivoting base rather than a tripod. The guy system attaches to the mast using an aluminum ring that slides over the mast.  The result is antenna system that performs better in some respects than the Buddipole, can at least theoretically configured to cover both the 80 meter and 160 meter bands, costs less, and is less vulnerable to damage than the commercial product. Downside? It weighs more – about 20 pounds for the total “kit including the mast, base and guys,  50 foot RG-8X coax, etc.

I also re-thought and re-configured the original Triple-Ratio Balun concept that has become part of the Buddipole system, turning it into a Sextuple-Ratio Balun (SIX impedance ratios!) using the same component set as the original. That project is described on a separate page of this web site.

I have spent approximately $150 total in materials to make this system, compared with almost $600 to purchase a comparable commercial kit (the Buddipole Deluxe plus TRSB,16 foot mast, guys, etc. And it has been fun to design, and construct, and use.

However, it would never have been possible without the inspiration of the original Buddipole. I would like to give a big “thank you” to Budd Drummond, who created the Buddipole, and to the company he formed that makes and sells these products. In the true spirit of ham radio, they encourage and support home-brew versions of their antenna system, even though it at last theoretically reduces their sales. My hat is off to them for their service to the amateur radio community. Please visit their web site and consider purchase of their product if home-brewing a complete antenna system isn’t something that lights your fire.



CONSTRUCTION NOTES

ALUMINUM TUBE ANTENNA ARMS

I often prowl the scrap bins at a local metal supply business.
One day they had a large number of 3/8” OD thick-walled aluminum tubing sections in the scrap bin, each 4 feet long. I grabbed them all, recognizing their potential for constructing VHF/UHF Yagi antennas, among other things. At scrap prices these tubes cost 90 cents each. (Similar tubing is available from DX Engineering in 6-foot lengths for $5.40 each, or about $2 per 2-foot segment including shipping.) I have built 2 meter and 70 cm Yagis with some of the tubing and still had a number of sections available. The inside diameter of these tubes is just the right size  (0.259”) for tapping with a 5/16”-18 TPI thread. Thus, sections of  the tubing can be joined with 1” lengths of 5/16-18 all-thread or carriage bolts with heads cut off. This assembly system provides a good alternative to the telescopic whips used in the commercial Buddipole system; I decided to define a “segment” as 24”, a good length to fit inside the 27” duffel bag I use to carry the disassembled antenna, and half the 4 foot length tubes. My complete system requires eight “whole segment” sections, plus two each of half, quarter, and eighth section lengths (12, 6, and 4 inches). I cut and tapped a pair of “arms” (the innermost component on each side of a dipole) that create a resonant 2 meter dipole when attached to the Tee, and a pair of shock-corded “long arms” that measure 0.945 meters, folding to half that length. A configuration with the “arm” plus the “long arm” on each side creates a dipole resonant at 50.125 mHz, the national calling frequency for 6 meter USB. The “long arms” are used in all other band configurations as well. The adjacent photo shows my bundle of antenna segments, two coils and my combined “Tee” and multi-impedance balun.

A collateral benefit of this construction method is that is practically ensures against membership in the infamous Broken Whip Club.  Although I ALWAYS guy this antenna because of the 16-foot mast,  did lose control of it a couple of times when first learning to set it up, and it fell without damage to the whips, except once.  The one time an element did break, the arm broke at the point where it mounts to the Tee; I simply cut the end off smooth and retapped it, losing 1/2 inch of Arm length – not enough to matter with any antenna configurations. If damage were worse, I could simply replace individual segments rather than the entire whip.


CONSTRUCTION OF THE “TEE” AND WHIP SUPPORT GUY STRUCTURE

Design and construction of a “Tee” that would mimic the
physical stability and configuration flexibility of the commercial Buddipole “Tee proved challenging. I considered just buying a Tee from Buddipole, but their product is designed using the standard antenna thread size of 3/8-24, which I couldn’t easily couple to my chosen aluminum tubing. So I “rolled my own.”
My“tee” is constructed of two blocks of 1” thick aluminum stock with one block of 1” thick clear acrylic plastic sandwiched in the center, to electrically isolate the two sides of the dipole from each other. The “sandwich” is held together securely with 1/4-20 bolts; 1/4” holes are drilled through all three blocks (clamped together to ensure alignment)
with 1//2” diameter holes drilled just deeply enough to recess the bolt heads and nuts. Each aluminum section is drilled and tapped to accept a 5/16-18 bolts oriented for the horizontal dipole arms (seen next to the “black” label in the photo at right).
These bolts are installed before the sandwich is bolted together.

The top of the “red” aluminum section (which connects to the center conductor on the coax cable) is drilled and tapped to insert a 1” long  5/16-18 stud (or sawed off bolt) which serves as the mount for vertical antenna configurations. A hole is drilled in the bottom, into the plastic center section about 1” deep, to accept the mast (in my project, 1” O.D. aluminum tubing).

The “black” side of the sandwich has a vertical stud of 1/4”-20 all-thread installed, onto which is screwed a 1/4-20 coupling nut, which in turn serves as the mounting point for a 2-foot long section of all-thread, ending in a 1” eye bolt, that provides an anchor point for two guys used to support the whip. This significantly reduces whip sag. The supporting guy is attached mid-way on each whip, and then clipped to the eye bolt. See accompanying photo and drawing for details. The guy attaches to the antenna with a small piece of sheet aluminum, drilled with two 5/16” holes and bent in a vice to a 45° angle, which slips over the threaded stud at the outer end of the first antenna section; it is held in place by the next section as it is screwed onto the assembly. The photo at right shows two antenna sections partially screwed together, for clarity.






COIL CONSTRUCTION

The primary coils are wound onto forms made from nominal 2” diameter black plastic plumbing pipe, which is 2.375 inches actual O.D. I wound 15.5 turns of #16 magnet wire onto the forms with 0.25 inch turn spacing; this produces coils with a calculated inductance of 8.0 µH; the actual coils, measured with an accurate inductance meter,  are 8.02 µH and 7.85 µH, due to small variations in winding precision. 8 µH is sufficient inductance for both horizontal dipole and vertical monopole configurations on 10 through 40 meters. (Coil are not used for 6 and 2 meter configurations.)  These are very efficient coils, with a calculated Q factor of 625 at 7.0 mHz. (Coil calculations are from a terrific web site, Hamwaves.) 

A larger coil would be required for an 80 meter vertical configuration I have modeled– about 55 µH inductance. This can be wound with 32 turns of #16 magnet wire on a length of 4” nominal diameter plastic plumbing pipe, actual O.D. 4.5 inches. With turns spaced 1/4” apart, the wound coil is 8” length, and has a calculated inductance of 55 µH at 3.5 mHz, with a Q factor of about 800.

A separate, even larger coil with about 150 µH inductance would be required for a 160 meter vertical. I have modeled this antenna, but have not built or tested it. The required coil could be constructed by winding 60 turns of #16 magnet wire onto a 4.5” OD plastic pipe at 6 turns per inch, or 10 inches of winding.  This calculates to provide 160 µH inductance at 2.0 mHz with a Q factor of about 750. The resulting antenna requires a tunable balun with an impedance setting of 3.125Ω, which is actually achievable, as described on my page discussing my “Sextupal Ratio Balun.”

Each coil end is brought inside the pipe through a small hole and then brought back out, to keep the end loop from coming loose. Wire ends are then fitted with ring terminals, which are slipped onto the end bolts  The end caps are drilled and tapped for 5/16-18 thread. Cap screws 1” long are screwed through the tapped hole in the pipe end cap, with the head inside. Each screw is tightened and then a 5/16 nut is scrwed down tightly on the bolt, locking the nut in place. The rung terminals for the coil, and the shorting wire at one end, are held in place with a second securely tightened nut, which is further held in place with a drop of glue.  About 1/2” of bolt thread protrudes, providing attachment points for the arm (which connects to he Tee) and to the Long Arm, the first segment in the Taps for the various number of turns that are required for different bands are added by folding small pieces of sheet copper around the magnet wire and then soldering them to the wire. (Insulated coating must be removed from the magnet wire at the solder point. Only a few turns must be tapped on each coil to provide taps at the necessary inductance to match each ham radio band. (See following discussion on modeling.) Coil impedance is selected by attaching an alligator clip to the appropriate coil tap, which is connected by stranded wire to one end of the coil, shorting out the unused coil turns.


MINIMIZING LOADING COIL IMPEDANCE WITH “DROOPERS”

Any antenna design involves tradeoffs. The coil-loaded dipole is no exception. Loading coils make possible a physically smaller antenna, but they also reduce the resistive radiation component of the impedance of any antenna. (This is the inherent impedance of antenna at resonance.)  The 40 and 30 meter horizontal dipole configurations with a Buddipole-style antenna presents a real challenge in configuration. You need either very long whips or high loading impedance. For example, with  8 µH loading coils (my maximum), the dipole spans an unwieldy 37 feet with the antenna resonant at 7.0 mHz. To achieve resonance with a more functional 26 foot span (the maximum I deploy), loading coils must be about 12 µH.  While this is certainly feasible,
a dipole with than much loading coil impedance presents an SWR of 2:1 or less over only a 25 kHz bandwidth.  Thus, it must be lowered and re-configured for any significant frequency change. So how do you lengthen the antenna electrically without extending the arms too far physically? My solution is to add “drooper” wires attached to the ends of each whip. The “droopers” are simply 2 meter lengths of stranded wire fitted with ring terminal connectors. These wires are attached to the end of the whips with 5/16-18 nuts that are screwed onto the last all-thread segment joiner in the configuration. With them, my antenna is physically 26 feet wide but electrically more than 38 feet long. With the longer arms less coil loading is required for resonance, and the useful SWR bandwidth more than doubles. It’s also very easy to “retune” the antenna by simply folding a portion of the drooper back upon itself to shorten it, holding the end in place with a small spring clamp paper clip. My drooper lengths vary from 1.9 meters to 1.5 meters within the 40 meter band. I can fine-tune the antenna to 1.1:1 SWR simply bt adjusting the drooper length. The diagram to the right shows modeling software output of the antenna geometry, with a non-connected “wire” added to indicate the position of the mast.

One might ask if this antenna is less efficient than an electrically equivalent dipole with straight arms. The answer is that one pays a very small price in lost gain for using droopers;  the drooper configuration loses less than 0.1 dBi of gain compared with non-drooper Buddipole configurations, virtually unnoticeable on a receiver S-meter. The reason this is true is showon in the diagram at right, which shows current flow in the antenna. There is very little current in the outer portions of a dipole, whether horizontal or vertical. However, one DOES pay a price in antenna bandwidth for loaded antennas. The unloaded 40 meter dipole, cut to resonance at 7.15 mHz and hung 16 feet in the air, has an SWR of about 1.9:1 at both band ends and thus is useful across the whole band. The drooper configuration has a 2:1 SWR bandwidth of 50 kHz, and the non-drooper version with shorter arms and higher impedance has only 25 kHz bandwidth. This means that you need five separate antenna configurations to tune across the band using droopers, and 10 without droopers. Put another way, if you tune the drooper antenna for resonance at 7.275 hHz, it will give you a useful SWR from 7.250 to 7.3 mHz, a substantial portion of the SSB portion of the band.  If you’re a CW fan, you can tune the antenna to 7.050 and work from 7.025 to 7.075 mHz with a single antenna setup – again, most of the spectrum used for CW.

And let’s be clear about one more thing: a 40 meter horizontal dipole16 feet above ground is a real cloud burner. It is a good configuration for NVIS work, but not for DX.  To achieve low-angle primary lobes on 40 meters, you need to set up your Buddipole as a vertical monopole (see below). The vertical has less overall gain, but greater gain on the low takeoff angles needed for DX.                                                        

(Of course, if you can get a conventional dipole high in the air, for example strung between two tall trees at 28 meters height, its performance will be much superior – more than 7 dBi maximum gain at a takeoff angle of 30° for good DX, and also a strong vertical lobe for NVIS work. In daylight with the F-layer about 250 miles high, an NVIS antenna will reflect back to the ground about 200 miles from your QTH, and the 30° takeoff about 850 miles. NVIS is excellent for shorter-range communication, especially if a mountain range intervenes between you and the other party in your QSO.)


SHOCK-CORD ALUMINUM MAST

The mast is constructed of 1” diameter anodized aluminum tubing, cut to 22” lengths and one end of each
(except the top segment) fitted with a 4” length of 1” I.D. heavy-wall aluminum tubing so that the overall length of each section is 24”, fitting into the same carrying bag as the antennas segments. The joint tube segments are attached to each mast segment with a1/4” zinc-plated bolt, lock
washer and nut so that half the joint segment slips over the tube to which it is attached and half extend beyond the mast tube, to accept the next segment in the mast. The mast has 8 segments. Seven are connected  together with about 11 feet of 1/4” diameter shock cord. I made loops on both ends of the shock cord. Then I threaded one loop into the first segment and positioned it so that the loop was pinned by the 1/4” connector bolt for the joint tubing, putting the bolt in place after the loop is positioned. I threaded the shock cord through all the mast segments except one, stretching the cord about 3 feet beyond the end of the next-to-last mast segment, and clamping it so that the end was not under tension. I slid the cord into the last mast segment, and pinned the loop with a 1/4” bolt  positioned about 6” above the bottom of this last (top) segment.  The entire mast collapses in seconds to a 24” length in a bundle about 8 inches in diameter, weighing 5 pounds. See the photo below for the folded bundle of mast elements and a photo at right (without antenna mounted) of the raised mast. Given that I am using a 16 foot mast, guying is essential. The non-connected section is useful for assembling the antenna; you can use a small pipe or stake driven into the ground, set the single mast section on it and then the Tee is at waist height, so you don’t have to bend over to pick up the antenna as you add each section of tubing to the configuration.

TILTING MAST BASE AND GUYING SYSTEM

Rather than trying to make a Buddipole-style tripod stand, which is really not useful for a 16-foot mast, I constructed a
pivoting base that holds the lower end of the mast in position while the mast is raised and lowered. The base requires two sections of aluminum L-stock, an aluminum plate about 6 x 12 inches, bolts to attach the L-stock to the plate, a short segment of heavy aluminum tubing 1.25” I.D., and a 3/8” diameter bolt to attach the heavy tubing and provide a pivot. See the accompanying photo. The base is held in position on the ground with four long nails driven into the ground with a mallet. The guys  ropes are 30 feet long, and attach to a steel washer intended for use with 1” diameter bolts, into which I drilled three 1/4” holes around the rim for attaching the guy ropes. The ring slips over the top mast segment and rests atop the joint section between the top two mast segments. Guy ropes clip onto the mounting ring at the upper end and have adjustable loops (taut-line hitch) at the other, so they  can be secured either to stakes or convenient tree limbs. The guy ropes are stored wound on small flat rectangles with Vs cut in the end, like kite string winder.


ASSEMBLING AND RAISING THE ANTENNA

I’ve learned there are many difficult ways to raise this antenna and one easy way. Atop a 16 foot mast, the antenna acts as though it were much heavier while the mast is partly raised, due to the large moment arm created by weight at the end of a long mast. Here’s my sequence of steps to raise it easily.

  1. 1.Assemble the antenna to the maximum length you’ll be using (full span = 26 feet) and lay it on the ground in a position where it is clear of bushes and trees and from which it can be raised to vertical without hitting bushes or trees. Attach the two mast brace guys to the mast at the appropriate point (see photo) and clip the other ends to the vertical guy support rod atop the Tee, adjusting tension of the guys by sliding the tent hitch knot that forms the loop in each guy.

  2. 2.Lay the mast on the ground with one end near the antenna Tee and the other end at the point where the mast will stand when raised vertically.

  3. 3.Slide the guy rope ring over the top mast segment, unwind the guy ropes, and position them so that one rope points away from the antenna, and each of the other two ropes are positioned to anchor about 120° from the first guy rope. Antenna anchor points will be 15 to 20 feet away from the antenna base, at roughly 6, 10 and 2 o’clock, with the mast pointing toward 12 o’clock. Without attaching the antenna, raise the mast to vertical, moving the mast base and adjusting the lengths of the 10 o’clock and 2 o’clock guys so that when they are taut, the mast is essentially vertical, but leaning very slightly toward the 6 o’clock guy stake, so that the mast, although pointing almost straight up, will hold itself in position with just the two guy ropes.

  4. 4.While the mast is standing on its own, adjust the length of the third guy rope so that it will attach to its stake or anchor point with a bit of tension.

  5. 5.Now –and only now – lift the mast slightly and slide the pivoting mount under it. Nail the mount to the ground with two to four long nails, depending on soil conditions.

  6. 6.Dis-attach the 6 o’clock guy from its stake. Keeping tension on that guy rope with your hand, walk toward the mast base. When you get to the mast, lower the mast to the ground so that the mast top is back where it began, next to the antenna Tee.

  7. 7.Slide the antenna tee onto the top of the mast, attach your coax cable to the balun, and run the cable along the mast to the mounting base. Secure the cable to the mast with a rubber tie strap.

  8. 8.Double-check all antenna settings, including coil shorting clip locations, settings of the PowerPole connectors on the balun, number of segments on each side of the antenna, and tightness of the coax connector. Double-check that the support guys that hold the antenna horizontally are properly tensioned.

  9. 9.Position yourself severeal feet “down” from the top of the mast and lift it with both hands. Gradually walk toward the antenna base, raising the antenna and moving your hands along the mast as you go; you are literally walking the antenna into vertical position.

  10. 10.When the antenna is vertical, is should stand without your support, leaning slightly away from the 10 o’clock and 2 o’clock guys. Now you can take the 6 o’clock guy and walk it into position and attach it to its stake or mounting point. Make minor adjustments in guy tension as required. The antennas should now stand in winds 50 mph or greater.

To lower the antenna either to change configuration or disassemble it, simply remove the 6 o’clock guy from its stake, walk back to the mast keeping slight tension on the loose guy with your hand, take hold of the mast, and walk it down to horizontal position. Before  you lower the antenna, make sure it’s rotated so that it will be horizontal (parallel to the ground) when it’s lowered. You don’t want to lower it onto one tip.

With a little experience, you will find that you can completely assemble and raise this antenna in about 10 minutes, and disassemble it slightly more rapidly. This is no doubt longer than it takes to perform the same functions with the commercial Buddipole, which benefits from telescoping whips.


A SMALL PORTABLE MANUAL ANTENNA TUNER

Especially on the lower bands, a tuner would help to extend the functional range of the antenna without having to lower it and change configuration.  A simple L-tuner (one capacitor and one coil) is sufficient. The coil is wired in series from the input to the output jack, and a tunable capacitor in shunt (from one jack to ground). Depending on whether the shunt capacitance is needed on the input or output sides of the tuner, the cables are simply switched leading to the antenna and the transmitter.  Details of such a tuner are described on a separate page of this web site.


VHF/UHF ANTENNAS

There has been quite a bit of discussion on the BUG on configuring the Buddipole
system for two meter work. I find it far easier to carry portable J-poles for 2 meters and higher bands, made from 450 Ω ladder line. Since most 2 meter work is FM and therefore vertically polarized, this is more efficient than a 2 meter horizontal dipole, and easier to set up; you can just hang it from any tree limb. The photo at right shows coiled-up 2 meter and 70 cm antennas.





MODELING THE ANTENNA SYSTEM TO DETERMINE CONFIGURATIONS

Having created the physical system to assemble my antennas, the next step was to develop antenna models for the Buddipole at various configurations. As a Mac user, I use cocoaNEC, the Mac adaptation of EZNEC created by Kok Chen,  W7AY.   I modeled dipole setups for every ham band from 2 meters through 40 meters, as well as verticals for 40 and 80 meters, and found that to configure the antenna for all ham band dipoles through 40 meters, I would need eight Full Sections (each 24 inches long), and two each of Half, Quarter, and Eighth Sections (12, 6 and 3 inches, respectively). Each coil required only three taps.  cocoaNEC output files for each antenna configuration are available here. In the real world, the antennas closely match the theoretical configuration, except that I can tune a broader portion of each band with tolerable SWR than the models indicate would be possible.


ANTENNA CONFIGURATIONS

Please note that the following antenna configurations are provided as examples only. If you make an antenna based on this description, it willl undoubtedly require slightly different configurations due to different coil impedances, different ground conditions, mast height, etc. I have a card with these configurations printed on the two sides, and it lives in the antenna carrying bag.

HF horizontal dipole antenna configurations listed below all use the Arm, Coil, Long Arm, plus indicated additional Segments on each side of the dipole;  On the higher frequency bands, some coil loading is used to reduce antenna resistance at resonance, even though a resonant antenna can be built without using the coil; without a coil, inherent impedance at resonance of dipoles exceeds 50Ω. These configurations were modeled using  “Average Ground” setting on cocoaNEC. Changing ground characteristics affects settings. For example, on 40 meters, the best balun setting is 22.2Ω over “poor ground” and 12.5Ω over “good ground.” Two configurations are provided for the 20 meter band – one using Droopers about 1.0 meters long, and the other without droopers. The former provides broader bandwidth and offers an acceptable SWR acrossthe band; the latter is easier to set up (no droopers) but does not tune the entire bandt under 2:1 SWR. Real-world setups closely matched modeled configurations on all bands.




Vertical configurations. The following configurations all mount a vertical monopole atop the mast.  The 6 and 10 meter configurations are intended for FM work, centered on the FM calling frequencies of 29.6 mHz and 50.3 mHz. Both use antenna elements mounted horizontally (as with a dipole) for the counterpoise, and a vertical  arrangement using Arm + Coil +  the given number of Segments. Best SWR is achieved on 6 meters with a segment length in between the smallest 4” increment available with 1/8 length segments (3 inches). To accomplish this fine tuning, I have cut a pair of segments to 7.5 inches,  which together give just the right length. 5/16-18 bolts could also be used to fine-tune the length of any antenna setup.)

The 160, 80 and 60 meter setups use a set of three counterpoise wires, each 30 feet long, mounted on the neutral (Black) side of the Tee, with the low end attached to a 24-inch length of non-conductive rod (fiber glass) set in the ground at a distance to keep the wires fairly taut, approximately 26 feet from the base of the mast; the three wires are arrayed along a 90°arc, providing modest directional gain opposite the counterpoise wires. The 40 meter setup uses two 30-foot counterpoise wires, set 90° apart. The 20 meter vertical uses a single 15 foot counterpoise. In my antenna kit, I have two counterpoise wires attached to one U-shaped crimp-on connector, and the third attached to a separate connector, so I can accommodate these various configurations.  The 20-meter counterpoise is the single wire folded back double on itself, and clipped to one of the three mast guys.  The illustration to the left shows cocoaNEC’s antenna geometry output for the three-counterpoise setup used for the 60, 75 and 80 meter band setups.

Note that although the 80/75 meter configurations have narrow bandwidths, a simple portable L-tuner, described here, can allow a single antenna configuration to tune the entire 75 meter band, and changing a coil tap provides coverage of the entire 3.5-3.75 mHz 80 meter band.