2023-F-007 | 9/1 Unun for multiband endfed non resonant longwire antennas

Function

The endfed multiband “longwire” antenna is a popular and simple wire antenna that is often used to be QRV rapidly on several different amateur radio frequency bands. Depending on the on-site possibilities, different wire lengths can be chosen. Lengths can vary between some 9 meters until the longest length feasible. Longer wire lengths give some gain, and allow more efficient use of the lower amateur radio bands.

Most of the time, the antenna wire is installed in an “Inverted L”, “or “sloping” configuration. The feedpoint impedance of such a “random” wire length (referred to ground) varies widely, depending on the frequency used and the setup shape of the antenna.

In order to transform the average feedpoint impedance of the antenna within the comfortable tuning range of a good a-symmetric antenna tuner, a 9/1 UNUN impedance transformer is often used. This transformer thus acts as a “Pre-Match Unit”.

Often, some experimenting is needed to achieve a good compromise and optimum results. Optimum results can be expected when the transformer is installed near the ground, with its “cold” side connected to a good RF ground. (i.e. ground rods with additional radials).

Mechanical Characteristics

• Optimized 61 mm diameter toroidal ferrites
• Heat resistant teflon coaxial cable with high breakdown voltage.
• Professional 50 Ohms N-connector or SO239 connector. (IP66 after sealing with self- vulcanizing tape or equivalent).
• Stainless steel M6 antenna connections. Stainless steel type 316 More info.
• Waterproof (IP64) and shock proof polycarbonate UV resistant enclosure. More info.
• Weight: +/- 500 g.

Electrical properties

• Impedance transformation ratio: 9/1
• Max. power:
• 2400 W PeP @ VSWR < 2.0/1 (ICAS)
• 1200 W PeP @ VSWR < 2.0/1 (CCS)
• For ICAS and CCS power definitions, More info
  
  
• Remark: For antenna VSWR values of > 2/1, some power de-rating has to be applied. As a rule of thumb, limit power to < 600 W PeP when VSWR is > 3/1 and limit to < 300 W Pep when VSWR is > 5/1.
• Deployable frequency range: 1.5 to 30 MHz.
• Insertion Loss: < 0.2 dB
• Intrinsic VSWR : < 1.4 / 1 at the frequency range edges.