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J-Pole Antennas

J-Pole Antennas. WB5CXC. J-Pole Antenna. J-Pole antennas are shorted end feed antennas. They consist of two elements, that are shorted together at the bottom. The shorter element is ¼ λ and the longer is ¾ λ . It is feed with 50 ohm coax, a little off the bottom of the shorted portion.

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J-Pole Antennas

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  1. J-Pole Antennas WB5CXC

  2. J-Pole Antenna • J-Pole antennas are shorted end feed antennas. • They consist of two elements, that are shorted together at the bottom. The shorter element is ¼ λ and the longer is ¾ λ. • It is feed with 50 ohm coax, a little off the bottom of the shorted portion. • The most common J-Pole is known as the ‘Copper Cactus’ because it is made from copper water pipe (and looks like a cactus).

  3. Copper Cactus • Copper Cactus can be made for 10M, 6M, 2M, 220, and 440. • The 10M J-Pole is very large and is probably impractical. • They are very popular on 6M and above.

  4. 70cm (440) Copper Cactus

  5. Adding Adjustment Bolts • Some of the articles add bolts to the J-Poles. These provide adjustments to the lengths of the elements. • I used the standard calculation and did a model of a 2M Copper Cactus. The SWR was probably within acceptable limits. • I then added some bolts and added some length (antenna too short). The first attempt proved the bolts are a good addition.

  6. SWR – built to formula SWR – used adjustment bolts (first try)

  7. Wire J-Poles • You can also make J-Poles out of wire. • Most are made from twinlead (flat TV cable) or ladder line. • Common Ladder Line comes in 300 or 450 Ohm. • You can use your standard formula for ladder line, but you have to use the velocity factor to get the final calculations.

  8. 300 ohm flat twinlead J-Pole

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