2.4kW 9:1 Unun for multiband end-fed non resonant long-wire antennas

If you're looking for high-quality random wire antennas to pair with your 9:1 UNUN, check out our selection here.

Function

The end-fed multiband “longwire” antenna is a simple yet effective wire antenna commonly used for rapid deployment on multiple amateur radio bands. The wire length can vary from approximately 9 meters to the longest practical length available. Longer wire lengths provide additional gain and improve efficiency, particularly on lower frequency bands.

Typically, the antenna wire is installed in an “Inverted L” or “Sloping” configuration. The feedpoint impedance of such a random-length wire (referenced to ground) fluctuates significantly depending on the operating frequency and antenna shape.

A 9:1 UNUN impedance transformer is employed to bring the average feedpoint impedance within the tuning range of an asymmetric antenna tuner. This transformer effectively functions as a “Pre-Match Unit.”

Experimentation may be required to achieve the best performance. Optimal results are obtained when the transformer is mounted close to the ground, with its “cold” side connected to a solid RF ground, such as a ground rod system with additional radials.

Mechanical Characteristics

• Optimized 61 mm diameter toroidal ferrite core.
• High-temperature-resistant Teflon coaxial cable with excellent dielectric strength.
• Professional-grade 50-ohm N-connector or SO-239 connector (IP66 rating when sealed with self-vulcanizing tape).
• Stainless steel M6 antenna terminals, made from corrosion-resistant 316 stainless steel.
• Durable, waterproof (IP64), and shock-resistant polycarbonate enclosure with UV protection. More info.
• Approximate weight: 500 g.

Electrical Properties

• Impedance transformation ratio: 9:1
• Maximum Power Ratings:
• 2400 W PEP @ VSWR < 2.0:1 (ICAS)
• 1200 W PEP @ VSWR < 2.0:1 (CCS)
• 850 W FT8/FT4 @ VSWR < 2.0:1
• For ICAS and CCS power definitions, refer to this guide.
• Important Note: For VSWR > 2:1, power de-rating is recommended:
  • VSWR > 3:1 → Limit power to < 600 W PEP.
  • VSWR > 5:1 → Limit power to < 300 W PEP.
• Operational frequency range: 1.5 to 30 MHz.
• Insertion loss: < 0.2 dB.
• Intrinsic VSWR: < 1.4:1 across the frequency range.

For additional documentation, visit our technical resources.