[Elecraft] KX1 Antenna Issues

[George, W5YR]

Sorry to rain on the parade, but while it is true that 30-j40 ohms is an
impedance with a magnitude of 50 ohms, it is a complex impedance. Referred
to 50 ohms resistive - which the transmitter requires -  it represents an
SWR of 3:1, not 1:1.

A few minutes with TLDetails, any t-lines program or a Smith Chart will show
this . . .

With that complex load, any transmission line will transform the impedance
to some other value Any line loss will reduce the SWR reading at the input.
A half-wave line section would repeat the impedance at its input, but the
SWR, referred to 50 ohms resistive, would still be 3:1.

This is a common shortcoming with instrumentation that can only measure the
magnitude of impedance, such as the early MFJ meters and noise bridges.

73, George W5YR
Fairview, TX
w5yr@att.net
http://www.w5yr.com


----- Original Message ----- 
From: "Pierre Desjardins" <ve2pid@sympatico.ca>
To: <elecraft@mailman.qth.net>
Sent: Wednesday, May 05, 2004 1:10 PM
Subject: [Elecraft] KX1 Antenna Issues


> **Correction on earlier posting..
>
> ...Lets say for instance that the load consists of a resistive part of 30
> ohms and a capacitive reactance of 40 ohms, or any right triangle
> combination giving the 50 ohms impedance matching (the case of an
improperly
> tuned vertical... or a wire near the ground or the extreme case of a dummy
> load).
> In each case, you will get a standing wave ratio of 1:1. So, that SWR
> reading of 1:1 often leads to false conclusions. By using a field strength
> meter you could find answers to your question.
>
> 72 de Pierre VE2PID
> (KX1 #442 working wonderfully with a random wire a few feet above ground
and
> a single radial)