=  NOW 30 WPM  =  TEXT IS FROM FEBRAURY 2023  QST  PAGE 34 =

RMS IS MEASURED, THE PEAK VOLTAGE WILL BE 14R14 V.  SELECTING THE PROPER
RESISTANCE WILL RESULT IN A 4R14 V DROP, AND 10 V WOULD BE MEASURED BY THE
INSTRUMENT.  THIS ACTS AS A VOLTAGE DIVIDER WITH THE PROBE AS ONE RESISTOR,
AND THE INPUT RESISTANCE OF THE MEASUREMENT DEVICE AS THE OTHER RESISTOR.
I NEEDED TO MEASURE HIGHER VOLTAGES, SO I ADDED ANOTHER PROBE SEE FIGURE 1
THAT WAS SWITCHABLE FOR 1X OR 10X.  THE 10X ALLOWS ME TO MEASURE VOLTAGES
UP TO 200 V.  USE CARBON COMPOSITION OR NON INDUCTIVE RESISTORS FOR THE
DIVIDER.  MEASUREMENT DEVICES I OPTED TO BUILD MY OWN MEASUREMENT HEADS
WITH INPUT RESISTANCES OF 10 M.  I BUILT AN ANALOG METER AND A MORE
ACCURATE DIGITAL READOUT METER.  BOTH ARE PORTABLE, AND EACH CAN USE A
STANDARD 9 V BATTERY OR A WALL WART.  THE ANALOG DC METER CIRCUIT SEE WWW.
ARRL. ORG/ QST IN DEPTH IS BASED ON AN ANALOG 0 TO 1 MA METER SEE FIGURE 2.
MY METER HAD A SCALE THAT WAS ALREADY LABELED WITH 0 TO 15 V.  I USED AN
LM324 QUAD OP AMP BECAUSE IT IS DESIGNED FOR OPERATION AT LOWER SUPPLY
VOLTAGES, AND IT HAS FOUR INDEPENDENT OP AMPS.  ONE SECTION OF THE OP AMP
IS CONFIGURED AS AN INVERTING AMPLIFIER.  THE GAIN IS SET AT 0R1 BY THE 10
=  END OF 30 WPM TEXT  =  QST DE W1AW  <