Z-Match vs AH-705 Tuner Efficiency for HF Doublet Antennas
Z-Match vs AH-705 Tuner Efficiency for HF Doublet Antennas
QRP and portable operators often ask if a manual Z-Match tuner is more efficient than an automatic Icom AH-705. The answer depends on tuner location, component quality, and common-mode current suppression. When each system is optimized, the efficiency difference is surprisingly small.
The Antenna Setup
We consider a center-fed doublet with 600 Ω open-wire feedline. Two common QRP tuner options are compared:
- AH-705 autotuner at the feedpoint, paired with a PTFE-based 1:1 current balun.
- Z-Match manual tuner, feeding balanced line directly, 80–10 m typical coverage.
With the AH-705 at the feedpoint and a balun insertion loss <0.07 dB (~1.6% loss), the efficiency gap nearly disappears.
Efficiency & Practical Performance
Tuner Location
- At shack: High SWR on long feedlines creates loss.
- At feedpoint: Both AH-705 and Z-Match avoid feedline loss and perform efficiently.
Balun Loss vs Internal Loss
- A PTFE-core 1:1 choke balun shows <0.07 dB loss, often lower than internal Z-Match losses at high reactance.
Matching Range
- AH-705: Covers 160–6 m.
- Z-Match: Generally 80–10 m.
Convenience
- AH-705: Fast, automatic, frequency-agile.
- Z-Match: Manual, slower, requires operator skill.
Common-Mode Rejection (CMR)
- A “balanced” Z-Match without a choke still passes CMC, raising noise and RF-in-shack risk.
- The AH-705 + quality 1:1 choke provides strong CMR and quieter reception.
- Add identical chokes to both, and CMR performance equalizes.
Measured Differences
On-air tests show the Z-Match may at best give ~0.05–0.1 dB advantage in narrow cases—inaudible. Occasionally it shows 1.5–2 dB (~½ S-point) higher RX levels due to slightly lower insertion loss, but the speed and agility of the AH-705 usually outweigh this in field or contest use.
Conclusion
With a high-end PTFE 1:1 balun at the feedpoint, the AH-705 is practically equal in efficiency to a Z-Match on a doublet. It adds wider band coverage, automation, and reliable CMR when paired with a proper choke. Unless weight/ultralight simplicity demands a manual tuner, the Z-Match no longer holds a significant advantage.
Mini-FAQ
- Is a Z-Match more efficient? — Only slightly, and only under narrow conditions. In optimized setups both perform equally.
- Does tuner location matter? — Yes. Place the tuner at the feedpoint to minimize feedline loss.
- Do I need a balun? — Yes. A high-quality 1:1 choke balun ensures efficiency and noise suppression.
- Which covers more bands? — The AH-705 covers 160–6 m; most Z-Match tuners stop at 80–10 m.
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