RF Frequency Counter | Microwave Frequency Counter

This page covers RF Frequency counter basics with block diagram. It describes down conversion techniques used in microwave frequency counter. The vendors and manufacturers of RF Microwave frequency counters are also mentioned.

As we know frequency of repetitive or periodic signal is defined by number of cycles per unit of time . If total n cycles appear in t time interval, then frequency is expressed as follows.
Frequency = n/t

Frequency is measured in Hertz or cycles/second. It can also be represented as ppm (or parts per million). The ppm and Hz are related as per following equation.
Frequency (Hz) = { Frequency (ppm) x RF Carrier Frequency (Hz)} x 10^-6

The figure-1 depicts block diagram of conventional frequency counter. As shown in the figure, total number of pulses counted by counting register in a pre-defined gate time gives frequency of input signal to be measured. In this block diagram open and close condition of main gate which is logical AND gate is controlled using oscillator. Mostly crystal oscillator of value 1 MHz or 5 MHz or 10 MHz is used here.

The calculated value of frequency is displayed on the numerical display.
For example, counting register value is 60,000 and gate time is 1 second. The frequency of signal is 60,000 Hz.

Down conversion techniques used in Microwave Frequency Counter

As we know frequency counter is a digital instrument and hence its frequency range is limited due to speed of logic circuits used. With current research in IC technologies, it is possible to have frequency counters upto 500 MHz or 1 GHz.

In order to have frequency counter above 1 GHz, different down conversion techniques are employed. Following are the techniques used in such microwave frequency counters.
➨Prescaling: Counters upto 1.5 GHz can be developed.
➨Heterodyne converter: Frequency counters upto 20 GHz can be developed.
➨Transfer Oscillator: Frequency counters upto 23 GHz can have this technique in its design.
➨Harmonic Heterodyne Converter: It is combination of both heterodyne and transfer oscillator. Frequency counters upto 40 GHz can be designed and developed using this technique.

Generic specifications of RF frequency counter

Following are the generic specifications of RF Frequency counter to be considered while selecting the right one for your need.
• Number of channels supported
• Frequency range of operation
• Input signal bandwidth supported
• Number of digits of resolution
• AC Coupled, DC Coupled or both
• Voltage input range and its sensitivity
• Accuracy of measuremnts
• Speed of measurements
• FM tolerance and AM tolerance
• External interface such as GPIB or IP connectivity
• Storage for measurements required for future comparisons

Vendors or Manufacturers of RF and Microwave Frequency Counter

Following table mentions RF and Microwave Frequency Counter Vendors or Manufacturers. Figure-2 depicts RF frequency counter model 53181A from Keysight technologies. The figure is used for representative purpose only, refer keysight website for more information on the product with detailed technical specifications and dimension.

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