getontheairRandom wire (non-resonant)
A random wire in this guide is a non-resonant length of wire plus a 9:1 UNUN plus a tuner. It is not an EFHW with the transformer swapped. The whole point is that the wire is not a half-wave on any band you care about, so the unun sees an impedance it can present to a tuner instead of a few-thousand-ohm brick.
Use this when the trees (or the AZ) will not accept a 66 ft EFHW. It is lossier than a resonant half-wave. Fine for 10 W. Think twice at 100 W into a match that is really a dummy load with extra wire.
The 4WAVE mast also uses a 9:1, but it is a vertical with a specified radial kit, not a random wire on a stick. Same matching idea, different geometry. Do not skip radials and call it “the same as 41 ft of wire.”
Why the length table exists
A half-wave (or multiple) on a target band puts a high impedance at the feed. The 9:1 is a broadband transformer, not magic. High-Z in still means a miserable match, a hot unun, and a tuner that either fails or turns power into heat.
So you pick lengths that avoid λ/2 on the bands you will actually use. The numbers below are field folklore that usually behave — starting points, not a manufacturer’s cut sheet. Measure with an analyzer after you hang it.
Lengths that usually behave: 29, 35.5, 41, 58, 71, 84 ft.
| Length | Typical reason people pack it |
|---|---|
| 29 / 35.5 ft | Tight picnic pad; ATU in the radio; 20–10 first |
| 41 ft | Common “fits a small park” compromise |
| 58 / 71 ft | More 40 m, still not a 66 ft half-wave |
| 84 ft | When you have the space but still want the tuner + 9:1 kit |
Avoid ~33 ft if 20 m is the money band (that is a 20 m half-wave). Avoid ~66 ft if you meant to build a random — that length wants a 49:1 and the EFHW chapter. A “random” that is accidentally a half-wave is the most common failure mode after a missing counterpoise.
Counterpoise / ground / radial
The 9:1 still needs a return. A random wire with no counterpoise uses the coax, the radio chassis, and your hand.
- Counterpoise on the grass: often 16–25 ft, laid out away from the radiator, not coiled at the feed. One is a start. Two or three, different lengths, is better.
- Ground rod: rare at a park and usually illegal to leave. A temporary stake can help. It is not a substitute for a counterpoise wire.
- Radials: if you are laying a radial field, you are most of the way to a vertical. The 4WAVE kit (12 / 17 / 33 ft) is the version this site actually specifies — 4WAVE.
Keep the counterpoise inside the boundary (and inside a SOTA 25 m AZ if that is the sitting). Flag the far end. Do not clothesline a trail.
Tuner in the radio vs at the feed
A 9:1 requires a tuner. The question is where the tuner sits.
- Internal ATU (G90, KX2, many shack radios): simple. The coax between unun and radio is part of the mismatch. Keep that jumper short. Fine at QRP and for a first outing.
- Remote / external ATU at the feed (LDG RT-100 class, AH-705, similar): the match happens where the impedance is ugly, so the coax runs 50 Ω. Less loss, less RF in the shack. Worth it when you run 50–100 W or the jumper would otherwise be long.
- IC-705: no HF ATU in the box. Pack an external or pick an EFHW on the bands it is cut for.
SWR at the radio after the tuner is “it loaded.” SWR before the tuner, at the unun, tells you whether the length is sane. If every band is 10:1 at the unun, change the wire or the counterpoise before you blame the radio.
When the 4WAVE 9:1 vertical is the same idea
A 9:1 plus a non-resonant radiator plus a tuner is the architecture. Stood up as a vertical with radials 12 / 17 / 33 ft and a hitch/RV/stealth mount, that architecture is 4WAVE. Hung as a sloper or inverted-L from a tree, it is this page.
Pick 4WAVE when the truck is in the unit, radials are legal, and you want low-angle 20–10 m. Pick a wire 9:1 when you cannot lay radials, cannot use a hitch, or the AZ is a boardwalk with one throw-line. Pick an EFHW when you can fit 66 ft and you want to leave the tuner in the bag.
Chooser: Antennas. Quarter-wave whip (no 9:1): Verticals.
Common failures
- Too-short counterpoise (or none). RF on the chassis, hot mic, a laptop that reboots when you key. Lay the 16–25 ft wire. Choke the coax at the unun.
- RF in the shack after that: jumper too long, choke at the radio instead of the feed, or you are sitting in the near field of a low horizontal. Shorten the jumper, move the choke, raise the wire.
- “Random” that is accidentally ½ wave on the band you CQ on. The unun runs warm, the tuner hunts, and 40 m never quite dips. Measure. Change length or admit you wanted an EFHW and put a 49:1 on.
- Power into a bad match. 9:1 + tuner is already lossy. 100 W into a 10:1 at the unun cooks ferrite. Start low.
Park rules still win. No wire across a trail, no unun at face height on a path, no tie-off on a monument — ethics.
Related
Habits / gotchas / checklist (random wire)
Notes & edits
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