AX1-Style Ultra-Portable HF Antenna
An AX1-style antenna is a pocket-sized, base-loaded HF whip built to clip directly onto a radio's antenna jack — no mast, no tripod, no guying, just a whip and coil small enough to disappear into a shirt pocket. Commercial versions run $100-150; this clone builds the same idea from a compact telescoping whip, a slug-tuned mini loading coil, and a short counterpoise. It's built for the operator who wants a legal contact from a park bench or trailhead with zero setup time, not for anyone chasing weak-signal DX — the tradeoff for that pocketability is real, and this guide is upfront about exactly how much performance you're giving up for it.
Extreme electrical shortening
At roughly 20 inches tall, this antenna is a tiny fraction of a resonant quarter-wave on every HF band it covers. On 20m the physical whip is about one-tenth of a quarter-wavelength, so the base coil has to supply nearly all of the missing electrical length — far more loading, relative to physical size, than either the Buddipole-style dipole or Buddistick-style vertical builds need.
20m (14.175 MHz): 16.5 ft vs. ~1.7 ft of actual whip here
Base-loading vs. center-loading
Current on a short antenna is highest near the feedpoint and tapers toward the tip. Putting the loading coil at the very base — where current is highest — means more of your transmit power is dissipated as heat in the coil's resistance than if that same coil sat further up the element, the way it does on the Buddipole/Buddistick builds. Base-loading is mechanically simpler and is what makes this design collapse to pocket size, but it's the less efficient of the two approaches, and it's the main reason this antenna trades away performance for size.
same solenoid relationship as any loading coil — but at this size, real coils are wound multi-layer on a slug-tuned form rather than a simple single-layer solenoid
Why ground quality matters even more here
Radiation resistance on an antenna this short is already very low, so any additional resistance in the ground/counterpoise return path eats a proportionally larger share of your power than it would on a longer antenna. A clip-on counterpoise or the radio's own chassis provides some return path, but a dedicated counterpoise wire measurably improves the picture.
- Radio chassis only: works, simplest setup, weakest performance of the options here.
- Short clip-on counterpoise (8-13 ft): meaningful improvement for modest added weight and setup time.
- Two counterpoises: further improvement, at the cost of the "clip it and go" simplicity that's the whole point of this design.
A good SWR is not the same as good performance
Matching and radiating are different problems. You can tune this antenna to a clean 1.5:1 and still be putting most of your power into coil and ground-loss heat instead of into the air — the analyzer confirms your feedline is happy, not that you're being heard. Treat the SWR dip as a necessary first step, not a measure of how well the antenna is actually performing.
| Section | Length (inches) | Length (mm) | Notes |
|---|---|---|---|
| Base coil form | 2.5 in | 64 mm | ~1 in OD, multi-layer wound, continuously adjustable via a threaded slug — not a fixed-tap coil |
| Whip, collapsed | 6 in | 152 mm | 4-section telescoping whip, threaded to mate with the coil form |
| Whip, fully extended | 18 in | 457 mm | Overall antenna height with coil ≈ 20.5 in |
| Counterpoise, short setting | 96 in | 2438 mm | ~8 ft, starting point for 15m-6m |
| Counterpoise, long setting | 156 in | 3962 mm | ~13 ft, starting point for 20m-17m |
AX1-Style Ultra-Portable HF Antenna Dimension Calculator
Materials for AX1-Style Ultra-Portable HF Antenna
Building the AX1-Style Ultra-Portable HF Antenna
This is a small-parts assembly job more than a construction project — most of the work is in the base adapter and the coil. There's no fixed tap table here, so plan on spending your build time with the analyzer instead of a wire cutter.
Source or wind the slug-tuned mini coil
Use a purchased slug-tuned mini loading coil (small mail-order and surplus sellers carry these) or wind one on a threaded ferrite/brass slug form, multi-layer, to fit the ~1 in × 2.5 in form factor. A single-layer air-wound coil at this size can't reach the inductance this build needs — this is a wound, tuned component, not a tap-and-clip coil.
Build the base connector assembly
Mount the coil form to a right-angle BNC-to-stud (or SO-239) adapter so the finished antenna threads straight onto the radio's antenna jack. Add a binding post or spring clip near the base for the counterpoise connection.
Attach the whip
Thread the telescoping whip onto the top of the coil form. Check that all four sections extend and lock smoothly before moving on — a sticky section is much easier to fix now than in the field.
Prepare the counterpoise wires
Cut one ~8 ft and one ~13 ft length of stranded insulated wire, terminating each with a banana plug or clip that fits your base binding post.
Mount to the radio and connect the counterpoise
Thread the assembly directly onto the radio's antenna jack, or onto a small stand if you'd rather keep it off the radio body. Clip on the counterpoise length appropriate to your band and let it hang or lay away from your body and the radio case.
Initial band setup
Extend the whip fully and thread the slug roughly halfway into the coil form as a starting point for any band. There's no turn-count table to fall back on here — the slug position and whip length interact, and both need to be found live against the analyzer.
Fine-tune resonance with an antenna analyzer
Sweep SWR and thread the slug in or out to move the resonant dip, using small adjustments — this coil is high-Q and reacts fast. Once you're close, fine-trim with whip extension rather than the slug for the last bit of movement.
Break down and pack
Collapse the whip, disconnect the counterpoise, and the whole assembly drops straight into a shirt or jacket pocket alongside the radio — that's the entire point of this build.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| High SWR on every band, slug won't help | Bad connection at the base adapter or coil | Check continuity from the connector center pin through the coil to the whip base | Re-solder or re-crimp the base adapter joints |
| Can't reach resonance at all on 20m or 17m | Coil doesn't have enough inductance for that band at this whip length | Confirm the slug is fully threaded in and the whip is fully extended | This may be a hard physical limit of your specific coil — a larger coil is the only fix |
| Good SWR, but very weak reports compared to a full-size antenna | Normal behavior for this design, not a fault | Compare against the -10 to -20 dB expectation set earlier | This is the tradeoff for the size — add a proper counterpoise if you're on chassis-only ground for some improvement |
| SWR shifts when you move the counterpoise | Counterpoise routing and length affect the tuned system | Compare a sweep with the counterpoise laid straight vs. coiled or near metal | Route the counterpoise straight and clear of metal, then re-tune |
| Resonance drifts as you touch or move the radio | Your body and the radio chassis are part of the ground system | Sweep with the radio in the exact position and grip you'll actually operate from | Always do final tuning in your real operating position, not on a bench |
| Whip section loose or wobbly | Worn or dirty telescoping section contacts | Check each section for play under light load | Clean contacts with contact cleaner; replace the whip if a section won't hold |
Why is efficiency so much worse than a full-size antenna?
The whip is a tiny fraction of a resonant wavelength, and the base-mounted loading coil sits where current is highest, so a larger share of your power turns into heat in the coil and ground path instead of radiating. That's the direct tradeoff for a 20-inch, pocket-sized antenna.
Can I extend this design to work on 40m?
Not with this build as described — 40m needs meaningfully more inductance than this compact coil and whip combination can practically provide. That's a separate, larger loading section outside the scope of this pocket-sized design.
Does a good SWR mean I'm getting good performance?
No — SWR only tells you the feedline is happy with the match, not how much of your power is actually being radiated. You can have a clean 1.5:1 and still be well down on effective radiated power compared to a full-size antenna.
Do I still need a counterpoise if I clip this to my handheld radio?
The radio's chassis and cabling provide some return path on their own, but adding a dedicated counterpoise wire measurably improves the match and performance over chassis-only grounding.
How close can I safely operate near this antenna?
Keep reasonable distance from the whip while transmitting, especially at higher power, since this design is often used held or clipped close to the operator. Check current RF exposure guidance for your specific power level and band.
Is this worth building over a compact wire antenna?
If setup time and pocket size are what matter most to you, yes. If you have even a few extra minutes and a tree branch or push-up mast available, a compact wire antenna like a linked dipole will outperform this design by a wide margin.