Efficient Holiday & Fixed-Mobile HF Operation — The Hybrid Approach
Many hams dream of a single “all-band” mobile antenna, but physics never cooperates. Short loaded whips are practical, yet their efficiency collapses below 20 m. Meanwhile, large doublets are superb performers—but less convenient to deploy on holiday. The most effective real-world strategy is to combine both systems, each covering the bands where it excels.
1. The Roof-Mounted 5.2 m Extendable Whip with Raised Radials
Mounted on the roof with four 2.6 m raised radials, the 5.2 m whip behaves as a ¼-wave vertical from 20 m upward. This gives clean, low-angle radiation ideal for DX and portable holiday operation.
Typical Performance (Resonant configuration)
| Band | Electrical length | Efficiency | Take-off angle |
|---|---|---|---|
| 20 m (14 MHz) | ¼ λ | ~88 % | ~20° |
| 17 m (18 MHz) | 0.30 λ | ~90 % | ~18° |
| 15 m (21 MHz) | 0.36 λ | ~92 % | ~15° |
| 12 m (24 MHz) | 0.41 λ | ~93 % | ~13° |
| 10 m (28 MHz) | 0.49 λ | ~94 % | ~11° |
| 6 m (50 MHz) | 0.88 λ | ~95 % | ~9° |
When You’re Feeling Lazy — Use It as a Tuned Random Vertical
For quick deployment, you can skip adjusting the whip and simply connect a 4 : 1 unun + tuner at the feedpoint. The unun transforms the whip’s 100–200 Ω feedpoint impedance closer to the tuner’s range. Efficiency will drop slightly because the antenna is now off-resonance and tuned reactively—but still very usable for portable work.
Efficiency Penalty (4 : 1 unun + tuner mode)
| Band | Approx. mismatch loss | Overall efficiency |
|---|---|---|
| 20 m | −0.8 dB | ~82 % |
| 17 m | −0.7 dB | ~83 % |
| 15 m | −1.0 dB | ~80 % |
| 12 m | −1.3 dB | ~77 % |
| 10 m | −1.6 dB | ~75 % |
| 6 m | −2.0 dB | ~70 % |
(Measured equivalent losses account for reactive tuning and transformation mismatch, not ground loss.)
This setup gives you an easy “holiday mode”: quick deployment, no whip adjustments, yet solid DX performance from 6–20 m.
---2. The 16 m Carbon-Mast Doublet for 160 m–30 m (and more)
For serious fixed-mobile or holiday base use, a 16 m carbon mast supports a center-fed doublet with 600 Ω open-wire feedline. Connected to a tuner (or 1 : 1 choke + unbalanced tuner), this provides near-lossless coverage of 160 m through 30 m, and acceptable performance even up to 10 m.
Low-Band Efficiency Highlights
| Band | Electrical height | Typical efficiency | Radiation angle |
|---|---|---|---|
| 160 m | ~0.1 λ | ~70 % | ~60° (NVIS) |
| 80 m | ~0.2 λ | ~85 % | ~45° |
| 60 m | ~0.27 λ | ~90 % | ~38° |
| 40 m | ~0.4 λ | ~92 % | ~30° |
| 30 m | ~0.53 λ | ~93 % | ~25° |
High-Band Use (20–10 m)
You can still use the same doublet up to 10 m, but the pattern becomes increasingly lobed, with deep nulls and rapidly changing feedpoint impedances. On 20 m the antenna behaves like a 1 λ dipole, already producing multiple azimuth lobes. On 10 m it’s nearly 3 λ long, forming many high-angle peaks.
The efficiency remains excellent (losses in open-wire feed are negligible), but usable coverage becomes direction-dependent. For general DX operation, the roof whip will usually outperform the doublet above 20 m because of its simpler, cleaner vertical pattern.
---3. The Ideal Mixed-Mobile Combination
| System | Bands | Best Use | Polarization | Efficiency |
|---|---|---|---|---|
| Whip + Radials (Resonant) | 6–20 m | DX & quick portable | Vertical | High (85–95 %) |
| Whip + 4 : 1 Unun + Tuner | 6–20 m | Holiday “lazy” mode | Vertical | Medium (70–85 %) |
| 16 m Doublet + Ladderline | 160–30 m | Low-band coverage | Horizontal | High (80–93 %) |
| 16 m Doublet (20–10 m) | 20–10 m | Directional multi-lobe | Horizontal | High but irregular |
By combining both systems, you maintain efficiency across the entire HF range—without the extreme compromises of typical mobile “screwdriver” or helical-loaded whips.
In short: whip = DX punch, doublet = low-band muscle. Together they form a full-spectrum, field-ready solution.
---Mini-FAQ
- Do I need a choke on the whip setup? — No, not if the four raised radials are resonant and symmetrically spaced; they naturally balance return currents.
- Can I use coax instead of ladder line on the doublet? — Only if the tuner is at the feedpoint. Otherwise, coax loss rises sharply under high SWR.
- What if I only have one mast? — The whip system can be roof-mounted; the doublet can be deployed between trees or a single 16 m mast with a lightweight center-insulator.
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