Thanks Dave - you are correct these were 1/2 wave radiators not 1/4 wave. I
did not describe the feed point details correctly either... memory here is not
what it used to be 😊 For 10m I used 16.5 ft #14 radiator fed from one leg of
a 7'-10" segment of 450 ohm window line that hung below the radiator. Tap the
coax into the window line about 6" or so off the lower end (adjust tap point
for best match) with the coax ground connected to the feed side leg and the
center conductor connected to the open side leg. Add a shorting strap to the
bottom of the window line. Choke the coax at the feed point, tape it up and
it's ready to go. Scale all the dimensions as desired for other bands.
73
Matt
KM5VI
-----Original Message-----
From: TowerTalk <towertalk-bounces@contesting.com> On Behalf Of David Gilbert
Sent: Wednesday, October 21, 2020 12:12 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] FW: Vertical dipole other choices?
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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