>Date: Fri, 15 Apr 2005 06:14:50 -0500
>From: "Grant Youngman" <nq5t@comcast.net>
>Subject: Re: [TenTec] LDG AT-100 Pro
>To: "'Discussion of Ten-Tec Equipment'"
><tentec@contesting.com>
> As I said to their rep, "How can one even accurately
measure
> 25 watts into an unknown antenna impedance?"
>There is certainly no problem measuring low power
>into any antenna Z.
Grant,
OK, I'll bite....
How does one accurately measure RF power into an
unknown impedance using the typical wattmeter either
internal or external to the rig?
All RF wattmeters that I know of are calibrated using
50 ohms as the standard impedance. As you deviate from
that 50 ohms, the calibration becomes meaningless.
Back when I worked in broadcasting, we calibrated
transmitter power by first using a common point
impedance bridge to measure the antenna system's
impedance, from that point on we could, of course,
calculate RF power.
The average ham doesn't have access to an impedance
bridge.
Doug/WA1TUT
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