[TenTec] What makes the 238 good or any other tuner good?

[Michael Tope]

----- Original Message ----- 
From: "Robert & Linda McGraw K4TAX" <RMcGraw at Blomand.Net>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Friday, January 20, 2006 5:00 PM
Subject: Re: [TenTec] What makes the 238 good or any other tuner good?


> Based on average antenna heights above ground for the average ham 
> location,
> for a 1/2 wave antenna operated on an even harmonic, the feed Z is 
> typically
> in the order of 1000 to 1500 ohms.  In theory, in free space, yes it is 
> much
> higher.  In practice, it isn't as high as one would imagine.  With 50 ohm
> coax the line SWR is ~30:1 while with some value of open wire line it is
> ~3.3:1.
>

I am curious, what are you basing that on, Bob? My
computer modeling suggests otherwise, but I am using
the NEC-2 engine, so I don't know how valid my data
is. The ARRL antenna book mentions that input R for
a 1 lambda dipole is a strong function of conductor
diameter, but it doesn't say much about height above
ground. In EZNEC (NEC-2 version), a 100ft long
dipole at 50 ft models out to about 6000 ohms input R
at the 1 lambda resonance. If you make the conductor
2" diameter it drops to about 2700 ohms. Droping the
antenna close to the ground shifted the resonant frequency,
but it didn't seem to low the input R significantly, but
I don't put strong faith in NEC-2 in this regime, so
perhaps there is more of an effect in the reality.

Mike, W4EF...............................................