First, please change the subject line when you change the topic. It's a
real PITA to keep track of what to read.
On Mon, 14 Nov 2005 19:11:45 -0600, Robert Chudek wrote:
>I have two questions:
>a) Where in the spectrum is this 248 foot hunk of wire resonant
anyway!?
> iv) can't be determined from the data,
It can't be determined from the limited data you've put in your email.
Remember my dissertation a few weeks ago about Smith charts. You can
measure Z, R, X, and VSWR at the end of the coax, but the coax
transforms that impedance. You said X was zero, but that is only the
definition of resonance AT THE ANTENNA. You've measured at the
transmitter end of the feedline, so that's not a meaningful result
unless the feedline is precisely a half wave long. What Z did you
measure at that low VSWR point? Was it within 25% of 50 ohms? If so,
that's probably the resonance of the antenna.
In general, for a dipole connected to coax, resonance is generally
pretty close to the minimum VSWR frequency.
>b) What will provide the best "performance" for this wire at 1830 KHz?
> i) Build a 2:1 matching device for the feedpoint,
> ii) Trim the legs shorter to move the minimum vswr to 1830 KHz,
> iii) Adjust the coax length to move the minimum vswr,
You first need to answer your first question, then move the resonance
to 1830, then measure Z. If Z is within about 50% of 50 ohms, a decent
antenna tuner ought to be able to handle it. If the VSWR relative to 50
ohms is below about 1.5 or 2:1, you may not need a tuner.
73,
Jim Brown K9YC
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