[AMRadio] Antenna/Coax


Donald Sanders w4bws at comcast.net
Sun Dec 31 13:18:41 EST 2006


The half wave dipole is 73 ohms at 1 wavelength above actual ground. At
normal heights, 30 to 60 feet, the antenna impedance is usually lower at
resonance. That being said, I use RG6U to feed a 80 meter dipole and have
less than 1.5:1 SWR in the phone band at resonance and a 200 KHz band width
for 2:1. So it is not all that critical in actual use, in my opinion.

Healthfully yours,
                          Don W4BWS
----- Original Message ----- 
From: "Jack Schmidling" <jack at schmidling.com>
To: "Discussion of AM Radio in the Amateur Service"
<amradio at mailman.qth.net>
Sent: Saturday, December 30, 2006 10:45 PM
Subject: [AMRadio] Antenna/Coax


> The more I read, the confusder I get.
>
> If a half wave dipole has a center feedpoint impedance of 73 ohms, why
> am I using 50 ohm coax.
>
> I just put my new EZ hang to use today and discovered that my coax is
> not long enough to take advantage of the much higher ends and is pulling
> the center down.
>
> I was going to buy a roll of RG8X but then learned that RG58U is good to
> over 430W so I might as well stick with this as weight is an issue.
>
> In the process of hunting up a source for coax I stumbled into this
> quandary.  Every source I look at says 73 ohms for a dipole.
>
> What am I missing?
>
> JACK K9ACT
>
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