Buddipole-Style Portable Dipole
A Buddipole-style portable dipole is a center-fed, coil-loaded antenna built from telescoping whip sections and a pair of tapped loading coils, designed to pack down to backpack size and re-tune across multiple HF bands from one set of hardware. Commercial versions run $200-300; this clone gets you the same working idea — a mast-mounted horizontal dipole or inverted-V that covers 40 through 6 meters — from off-the-shelf whips, magnet wire, and PVC stock. It's the antenna most SOTA and POTA activators reach for when they want one antenna instead of a bag full of band-specific wire dipoles, and it's a good next build once you've already put up a full-size wire dipole and want to understand how loaded, electrically-shortened elements actually work.
Physical length vs. electrical length
A resonant half-wave dipole is set by wavelength, not by how much whip you're willing to carry. On 40m that's over 32 feet per leg — far more than any telescoping whip you'd want on a backpack. A loaded portable dipole accepts that the physical element will stay short on every band, and uses a coil partway up each arm to supply the missing electrical length instead of missing wire.
40m (7.15 MHz): 468 / 7.15 = 65.5 ft total → 32.7 ft per leg
How the loading coil makes up the difference
A physically short element looks capacitively reactive at its feedpoint instead of resonant. A series loading coil adds inductive reactance to cancel that, moving the resonant point back down to your operating frequency. More missing length means more turns; less missing length (higher bands) means fewer turns. Wheeler's classic solenoid approximation is what coil winders actually use to get a starting turn count before touching it up on the antenna.
d, l in inches; n = turns — accurate to roughly ±5% for practical d/l ratios
Horizontal, inverted-V, or vertical
The same coil-and-whip arms support more than one configuration once mounted on a mast:
- Horizontal dipole: both arms level, cleanest figure-8 pattern, needs two support points or a center mast plus guyed ends.
- Inverted-V: arms drooped 30-45° below horizontal from a single center mast, more forgiving in the field, slightly lower feedpoint impedance than flat-top.
- Vertical (asymmetric): one arm vertical against a ground-plane or counterpoise wire instead of a matching second arm — a different feedpoint and matching problem, covered separately in the Buddistick-style build.
Why 40m is touchier to tune than 10m
Radiation resistance on a fixed physical length falls off with the square of how small a fraction of a wavelength that length represents. On 40m your 9-foot arm is a tiny sliver of a wavelength, so radiation resistance is low, coil losses matter more, and the SWR bandwidth is narrow. On 10m the same arm is a much bigger fraction of the wavelength, so it behaves closer to a full-size element — wider bandwidth, less coil dependence, easier to tune.
same physical arm → far smaller fraction of λ on 40m than on 10m
| Section | Length (inches) | Length (mm) | Notes |
|---|---|---|---|
| Fixed stub (feed to coil base) | 12 in | 305 mm | Same on both arms, non-adjustable |
| Coil form (winding length) | 4 in | 102 mm | 96 turns max, #18 AWG enameled wire, 24 turns/in |
| 40m whip extension | 96 in | 2438 mm | 96 turns engaged (~79 µH); tip-to-tip ≈ 18.7 ft |
| 30m whip extension | 96 in | 2438 mm | 72 turns engaged (~57 µH); tip-to-tip ≈ 18.7 ft |
| 20m whip extension | 96 in | 2438 mm | 60 turns engaged (~46 µH); tip-to-tip ≈ 18.7 ft |
| 17m whip extension | 96 in | 2438 mm | 48 turns engaged (~35 µH); tip-to-tip ≈ 18.7 ft |
| 15m whip extension | 96 in | 2438 mm | 36 turns engaged (~25 µH); tip-to-tip ≈ 18.7 ft |
| 12m whip extension | 96 in | 2438 mm | 16 turns engaged (~8 µH); tip-to-tip ≈ 18.7 ft |
| 10m whip extension | 82 in | 2083 mm | 6 turns engaged (~2 µH); tip-to-tip ≈ 16.3 ft |
| 6m whip extension | 40 in | 1016 mm | Coil bypassed (0 turns); tip-to-tip ≈ 9.3 ft |
Buddipole-Style Portable Dipole Dimension Calculator
Materials for Buddipole-Style Portable Dipole
Building the Buddipole-Style Portable Dipole
Basic soldering and hand-tool skills are all this build needs. The part that separates a good result from a frustrating one is patience during the final tuning step — budget real time for it and don't skip the analyzer.
Cut and prep the coil forms
Cut two 4 in lengths of 1.25 in OD Schedule 40 PVC. Mark and drill small tap holes along the winding area at the turn counts you'll need (6, 16, 36, 48, 60, 72, 96 turns from the feed end), sized for the wire you're using plus a tap lead.
Wind the loading coils
Anchor the wire end, then close-wind 96 turns of #18 AWG enameled magnet wire per form at roughly 24 turns per inch, keeping tension even. At each marked tap point, pull a small loop through the drilled hole, scrape the enamel off, and solder on a short tap lead before continuing the winding.
Build the center feedpoint with a common-mode choke
Mount an SO-239 (or binding posts) to your feedpoint bracket, with the two arms wired to opposite sides. Wind 8-10 turns of your coax jumper on the FT240-43 toroid right at the feedpoint before it runs to your radio — this is the choke that keeps RF off the outside of the coax.
Assemble each arm
Build each arm as stub (12 in, connects to the feedpoint bracket) → coil form → telescoping whip, in that order from the feedpoint out. Solder or clamp solid connections at both ends of each coil — a loose coil-to-stub or coil-to-whip joint is the single most common source of erratic SWR on this design.
Wire and label the coil taps
Bring a tap lead out from each drilled tap point to an alligator clip (or a wired position on a rotary switch if you built one). Label each tap clearly with its target band using the turn counts in the dimensions table — you'll be changing these in the field, often with cold hands.
Mount to a mast or tripod
Attach the feedpoint bracket to your mast via the tripod-thread adapter or clamp. Run the coax jumper down the mast to your choke and radio, leaving enough slack that mast adjustments don't strain the feedpoint connections.
Choose your configuration
For a flat-top horizontal dipole, guy or support both arm tips near the same height. For an inverted-V, let both arms droop 30-45° from the mast-top feedpoint — this needs only the one center support and is the faster field setup.
Set the starting whip extension and coil tap
Using the dimensions table, extend both whips to the same length and clip both taps to the same turn count for your target band — symmetry between the two arms matters more than hitting the exact number on the first try.
Fine-tune resonance with an antenna analyzer
Sweep SWR and note where the dip actually falls. If it's low in frequency, retract the whips slightly (equally on both sides); if it's high in frequency, extend them. Only move the coil tap if you're out of whip travel in either direction. Re-check after every band change — the table gets you close, the analyzer gets you resonant.
Break down and pack for the field
Collapse both whips, disconnect the tap clips, and fold the arms in at the feedpoint bracket for transport. A padded tube bag protects the coil windings, which are the one part of this build you don't want crushed in a pack.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| High SWR (3:1+) on every band, no tap helps | Bad feedpoint or choke connection | Check continuity from center pin through to each whip stub | Re-solder feedpoint joints; check choke winding for a short to the form |
| Can't get below 2:1 on 40m/30m at max tap | Coil undersized or whip not fully extended | Confirm whip is fully extended and the tap clip contacts the last turn cleanly | Add a few more turns to the coil or clean/re-seat the top tap connection |
| SWR swings sharply with a 1 in whip movement | Normal behavior for a loaded low-band element | Low radiation resistance and high Q are expected on 40m/30m | Tune in small increments with the analyzer; budget extra time on the low bands |
| Resonant on the bench, high SWR once mounted | Mast, tripod, or nearby metal detuning the antenna | Compare a bench sweep to a sweep in the actual deployed position | Always do final tuning in the real setup, and keep the coils clear of the mast |
| Coil gets noticeably warm after extended transmit | High circulating current in a low-band coil at high power | Check power level and duty cycle against the #18 AWG wire's rating | Back off power on 40m/30m for long keydown modes, or rewind with heavier wire |
| SWR spikes intermittently while operating | Dirty or loose telescoping whip section contacts | Wiggle each whip section under load while watching SWR | Clean contacts with contact cleaner and add slight tension to loose sections |
Can I run 100 watts through this?
Yes for typical SSB and CW duty cycles with #18 AWG coil wire. Back off power on 40m and 30m for long keydown modes like RTTY or FT8, since those bands run the most current through the biggest coil.
Why is this less efficient than a full-size wire dipole?
A physically short, loaded element has lower radiation resistance than a full-size half-wave, so a larger share of your power is lost as heat in the coil rather than radiated. That loss is worst on 40m and shrinks as you move up in frequency, which is why the -1 to -3 dB figure is a range, not a fixed number.
Can I set this up as a vertical instead?
This horizontal/inverted-V build isn't optimized for it — a true vertical needs an asymmetric feedpoint with a counterpoise or ground-plane wire instead of a matching second arm. That's a different design (Buddistick-style), not this one.
What mast height works best?
15-25 ft gets you clear of nearby obstructions and gives a reasonable low-angle takeoff on the higher bands. Even 10 ft on a photo light stand will work for NVIS-style short-skip contacts on 40m.
Can I add 80m coverage?
Only with an add-on loading section carrying significantly more inductance than the coils in this build, and efficiency drops further at that point. Most builders treat 80m as outside this design's practical range and use a dedicated 80m antenna instead.
How tight does the coil winding need to be?
Close-wound and even is what the 24 turns/in figure in the dimensions table assumes. Gaps between turns lower the inductance per turn, which is the most common reason a homebrew coil needs more turns than the table predicts to hit resonance.