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Project Notes

#466 VC3165

All about the Victor VC3165 frequency counter.



I’ve been using the Victor VC3165 frequency counter for some time, and it’s proven a very reliable bit of kit. I’ve used it mainly for signals from DC to a few hundred MHz, though it’s range does extend to 2.4GHz.

I purchased mine from Instruments World Store on aliexpress.

What follows is an overview of the operation and a bit of a look at the internals of the unit.


The instrument uses a standard enclosure. Front and rear panels are well layed out, although the gate control knob below the channel inputs can be inconvenient to get to with leads attached.

The unit I received had some button labels only in Chinese, so I’ve stuck on my own labels in English. A manual is available electronically in English which helped!



A look inside the case:


Function and Counter Modes

The function key selects between 3 modes. The input channel used depends on the mode:

Function Coupling Freq. Range Gate time min Gate time max. Channel
1 AC 1GHz-2.4GHz 1kHz 100Hz B
1 AC 50MHz-1GHz 1kHz 10Hz B
2 AC 2MHz-50MHz 1kHz 10Hz A
3 AC 100Hz-2MHz 10Hz 0.1Hz A
3 DC 0.01Hz-100Hz 0.001Hz 0.001Hz A

AC/DC Switch

In mode 3, the AC/DC switch selects between low frequency AC signals and verl low frequncy DC signals (DC measurement is required for anything under 100Hz).

Gate Control

The gate control knob adjusts the gate time (range depends on the mode). This can be important for correctly locking on to a signal with the required accuracy.

  • short gate time: faster measurement, but resolution is lower
  • longer gate time: slower measurement, but higher resolution

Power Supply

The VC3165 has a low noise linear power supply. Mains power is stepped-down with a transformer with primary windings switchable for 220V/110V.

The approximately 9V AC is regulated to 5V with a KA78R05 low-dropout voltage regulator.

Main Board

I haven’t traced out the circuit, but interesting to note that it appears to be a version of a conventional CMOS counter design, with an AT89C4051 microprocessor in control.

The main clock source is in a shielded housing. This may even be a temperature-controlled “crystal oven” but I’m not sure. There’s been some thought put to providing good shielding:

  • top cover is lined with a ground plane
  • each input front end circuit is in it’s own shielded housing

IC listing:

  • AT89C4051 CMOS 8-bit microcontroller with 4KB of flash
  • 74F74PC dual D positive edge triggered flip-flop, asynchronous preset and clear
  • 74LS373N octal transparent latch
  • 74HC393N dual 4-bit binary counter
  • 74HC153N dual 4-line to 1-line data selector/multiplexer, non-inverting outputs
  • 7555 CMOS 555 timer
  • LM393 Dual Differential Comparator
  • KA78R05 5V low-dropout voltage regulator


The front display board has a Microchip CF775-04/P (I think a PIC variant) specialised for display control.

Credits and References

Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.