[TowerTalk] Measurement errors and power line taps. Was, AL-80 Power Taps...

[Jim Jarvis]

TT:

Have privately commented to AD1L that I would go to the
middle tap, to start.  The 240v tap is the most aggressive,
resulting in the highest Ep & Eg.  

While this isn't relevant to antennas, the discussion IS relevant 
to measurement, and there is a comment that bears making.

The DMM he's using probably has an AC accuracy of +/- 3-5%.
That is, +/- 7-12V error @ 240V.  We're discussing power grid variations
of between 0.8 and 3%....  Anybody see a disconnect here?

My recommendation was to pick the mid-tap, and only make changes
if the amp voltages suggested it was necessary.  You're dependent
on the accuracy of the DC meters in the amp, in any case.  If they
don't look wierd, you won't make a change.  If they mis-read, you
won't know any better!  But they're probably ok to 2% or so. 
Fortunately, tubes are fairly forgiving. 

The relevant point to towers and antennas?  If you're going to 
make a data-driven decision, you need to know the accuracy of
your data, whether it's physical loading, vswr, f/b, gain, or
Vac.  

Now, which way is true North?

N2EA
Jim Jarvis, President
The Morse Group, LLC
We create high-performance organizations.
jimjarvis at themorsegroup.net
www.themorsegroup.net