22 March 2015
BUILD IT YOURSELF
Frequency counters have been around for many years as a standard piece of test
equipment in both commercial and hobby labs. It has evolved to remarkable levels of
accuracy that are several orders of magnitude higher than most hobbyists could ever
use. For example, I borrowed an Agilent 53131 counter to test the design of this
project. The 53131 displays up to 10/11 digits of frequency that translates to reading
a 10 MHz signal to .001 Hz! Counters of this type use advanced circuits called
interpolators that correct the ±1 count tolerance normally stated in spec sheets. My
design target for this project was seven digits, so a 10 MHz input signal could be
accurate to 1 Hz, and a 10 Hz signal be accurate to .00001 Hz using a one second
measurement time (without an interpolator).
BUILD A FREQUENCY
COUNTER
By Jim Teixeira
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