#741 PLJ-1601 Frequency Counter

Testing the PLJ-1601-C 0.1MHz-1.2GHz Frequency counter.

Build

Notes

I bought the “PLJ-1601-C 0.1MHz-1.2GHz Frequency counter” back in 2015 for SGD$15.99 but haven’t used it much beyond an unboxing test. IIRC, it didn’t seem that accurate or useful so it got put aside…

I just dug it out again, and finally figured out some of the “magic settings” required to get it to work properly. It is not so bad after all! Now it just needs a case or base…

Long story short, the two settings I made to get it working well:

disable the filter for signals below 3MHz
make sure the reference is set to 13 MHz internal benchmark. It seems that by default it was set for 12.8 MHz external benchmark.

And two important things to note:

the signal input ground line is actually connected to power ground, so be careful when interconnecting equipment.
the JST connector for the input signal is wired the reverse of the more common convention, so beware of accidentally shorting to ground.

Product Specs

The original seller listing is long gone, but I’ve seen it listed recently on amazon and alibaba:

It seems the PLJ-1601 has since been superseded by the PLJ-0802-E e.g. https://www.aliexpress.com/item/1005008750872275.html

I found some manuals for the PLJ-1601 on the 2e0dfu blog: https://2e0dfu.wordpress.com/2016/10/09/plj-1601-c-frequency-counter-manual-english-language-version/. these were invaluable for getting the device working effectively. For posterity, I’ve mirrored the manuals here:

Test Circuit

For testing, I’m using an FY3200S signal generator set for a 0.4V peak-peak sine wave through a simple attenuation circuit as follows:

schematic

Tests

My first tests were not great. Measured values are noticeably off. For example, a 6 MHz sine measuring 5.9 MHz:

test01a

The scope shows the signal source is really bang-on 6 MHz:

test-signal

Making Adjustments

After reading the manual, I switched the reference to 13 MHz internal benchmark (through the on-screen menu). It seems that by default it was set for 12.8 MHz external benchmark.

And now … oh, my: measurements are spot on:

test01b

Going below 3 MHz, it is necessary to turn off the filter (through the on-screen menu).

test01c

At the upper end of the signal generator range (24 MHz), measurements are starting to get a little off:

test01d

Project Notes