That's not really a J-Pole. A J-Pole generally has a 1/2 wave vertical
section, not a 1/4 wave. Since the end of a half wave is high
impedance, the ladder line is used to get a match. If you only have a
1/4 wave vertical you don't need any ladder line to feed it ... a single
wire of the proper length as a counterpoise works fine.
73,
Dave AB7E
On 10/20/2020 9:58 PM, maflukey@gmail.com wrote:
You can also feed a 1/4 wave wire with the feed point grounded to one leg of a
piece of 450 ohm window line and then short the bottom end of the window line
at the appropriate length to make an elevated J-pole. Leave the top of the
other leg of the window line open. Essentially unity gain, much like a
vertical dipole, but easy enough to hoist up into tall trees.
Matt
KM5VI
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