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Re: [Amps] About LP100A

Subject: Re: [Amps] About LP100A
From: "Roger (K8RI)" <>
Date: Mon, 19 Jun 2017 04:36:43 -0400
List-post: <>
Be careful of the scope across a known load. Accuracy depends on the precision of the resistor and on many bands may require compensation. If you have a good dummy load, there is the calibration of the load.My DL5K requires compensation above 40 meters. It's great on 160, 75, and 40, but the SWR goes up in a hurry from there.

73, Roger (K8RI)

On 6/18/2017 Sunday 9:36 PM, Jim Brown wrote:
Hi Jim,

You've pointed out the obvious problem -- man who has more than one watch never knows what time it is. :)

My LP100A came from the estate of an SK, with one coupler. I sent the LP100A and the coupler to Larry to cal for me, and to cal the second coupler that I bought. So I know it's calibrated. For the LP100A, the cables between the coupler and the unit are part of the calibration, and they're labeled.

Your MB-1 calibration using the scope across a known load is pretty good, as good as the calibration of the scope and the load.. :) It really does come down to using the tools and instrumentation in our own personal labs to get as close as practical to the fundamentals of what we're measuring.

73, Jim K9YC

On Sun,6/18/2017 5:28 PM, MU 4CX250B wrote:
I have an LP100A wattmeter and like it very much. But how do any of
you know how accurate it really is? The only way to know is with a
calibration standard, and RF power is notoriously difficult to measure
accurately. I've compared the LP100A to the Alpha 4510, and a
MeterBuilder MB-1, and by measuring the RMS RF voltage (with a
calibrated Tek oscilloscope) across a 50 ohm dummy load. There's no
obvious consistency among these wattmeters. The readings vary from one
another with frequency and power level, by as much as five percent. My
guess is that the MB-1 is likely the most accurate, based on the
calibration curves and methodology supplied by the manufacturer. But
that is still just a guess.

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