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Re: [Amps] About LP100A

To: "Roger (K8RI)" <>
Subject: Re: [Amps] About LP100A
From: MU 4CX250B <>
Date: Mon, 19 Jun 2017 08:10:50 -0600
List-post: <>
I used a Bird dummy load, rated to above 1 GHz. The Scope was a
recently calibrated Tek 2465B. I'd estimate overall measurement
accuracy to about 3%.
Jim w8zr

Sent from my iPhone

> On Jun 19, 2017, at 2:37 AM, Roger (K8RI) <> wrote:
> 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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