[Amps] About LP100A

[Jim Brown]

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.