What is a Frequency Counter

A frequency counter is an electronic instrument that measures the frequency of an input signal. Frequency is defined as the number of cycles per second of a periodic signal and is measured in hertz (Hz).

Traditionally Electronic Counters have been divided into 4 sub categories:

• Frequency-only counters with 1 standard input channel measuring frequency and related parameters (Period)
• Timer/Counters or Universal Frequency Counters with 2 standard input channels measuring frequency, plus time interval (start-stop) between the 2 channels, and related parameters (Period, Pulse Width, Rise/Fall Time, Duty Cycle)
• Microwave Counters measuring frequency in the microwave or millimeter wave frequency range
• Time Interval Analyzers focusing on high resolution & high speed gap-free time Interval measurements. These instruments are mainly PCI or PXI boards needing a special main frame

Modern counter categories from the 2000s are:

• Graphical Timer/Counter/Analyzers which are advanced timer/counters with a high-speed internal result memory, and graphical display of modulation and trend (“Frequencyscope”)
• Multi-channel Frequency Analyzers, which are a combination of Graphical Counter/Analyzers and Time Interval Analyzers, with multiple parallel independent input channels performing high-resolution and high-speed gap-free measurements.

 Applications

• Calibration Laboratories: Used to calibrate frequency sources and for precise comparisons of atomic clocks
• Aerospace and Defense industry: Used to verify critical performance of e.g. radars in development and production test
• Defense organizations: Used as field calibration tools for military electronic equipment, and as time and frequency calibration tool in calibration labs
• Science and Research: Used in various scientific research fields where precise timing and frequency measurements are necessary.
• Electronics Industry: Used in laboratories, production test, and fieldwork to develop and test electronic devices, modules and components
• Communications: Ensures accurate frequency in transmitters and receivers, critical for proper communication.

What is resolution?

Resolution – Resolution is the measurement instrument’s ability to discern between measurement results that are close to each other. The higher the resolution, the smaller differences between individual values can be detected. Compare a church clock (resolution = 1 minute) with an electronic stop watch capable of registering 1/1000 of a second (1 millisecond).
In a Frequency Counter Analyzer, the time interval resolution is normally given as “ps (rms)”, and calculated as the standard deviation of a large number of samples of a fixed time interval, e.g. a cable delay in constant temperature.

What is accuracy?

Accuracy – Accuracy is the deviation from the “true value”, the calibration standard. Accuracy is often, but not always, correlated to resolution. A high resolution digital clock with a poor crystal oscillator may show a time that is ten minutes or more off after a year. A church clock could be more accurate (but however the resolution is bad)

What is traceable calibration?

Calibration – Calibration is the process of measuring the uncertainty of an instrument by comparison with a calibration standard. The purpose is to find out the deviation of the instrument to be able to correct measured values. Note that Calibration is only about finding the deviation to the “true value” (= the calibration standard). If you also want to correct your instrument, to minimize the deviation, then you are doing an Adjustment.

A calibration can be traceable, if the calibration standards used have been compared (calibrated) to international standards. A traceable calibration means that you know how accurate your used standards are

Why is synchronization important?

Synchronization – Synchronization can be described as “perfect timing” of signals. E.g. the receiving end of a communications link must have exactly the same clock frequency as the transmitting end. Imagine bringing together the best musicians in the world, without calling in a conductor to synchronize (conducting) the ensemble. You would never get the best out of the musicians. And a communications network consisting of the best network elements in the world would never have the optimal performance characteristics without synchronization of the signals.

Synchronization can mean Frequency synchronization, where you synchronize all elements in a network to run at the same frequency, for example classical telecom networks, SDH, SONET, PDH, and wireless GSM, 3G, 4G, 5G.

It could sometimes also mean Time synchronization, where you want network elements to act at the same time, for example time-stamping of financial transactions, or delivering a time scale to a remote location, for example IRIG time codes, PTP, NTP.

What is frequency hopping?

Frequency Hopping – Hopping frequencies can be described as a dynamic frequency change where an information-bearing signal is being forced to change its carrier frequency on a regular basis (Several times per second). This is to avoid unauthorized signal capture, and is used by e.g. the military. It is also used to make communication safer, by avoiding shadow effect at certain frequencies, and is used in e.g. GSM, some older wireless LAN:s, etc.

What is modulation?

Modulation – Modulation is the process where some characteristics of a wave (the carrier wave) is made to vary in accordance with an information-bearing signal wave (the modulating wave). If the amplitude of the carrier wave varies in accordance to the modulating wave it is called amplitude modulation, or AM. If the frequency of the carrier varies instead, it is called frequency modulation or FM. If the phase of the carrier varies, it is called phase modulation, or PM (M).

Why is the trend display in CNT-90 so “unstable”. A very stable constant frequency fills the whole display.

Trend display – In CNT-90 the graphics trend display (frequency vs. time) is auto-scaled, meaning the display window will always be “filled from top to bottom”. The highest and lowest value during the capture determines the display area, even if the frequency is extremely stable.
To set the display range manually, use the Limits function to define the Y-scale in Trend mode (and the X-scale in Histogram mode)

What is jitter?

Jitter – Jitter is a “faster” form of wander. Jitter variations occur over a period of time less than 0.1s (10 Hz). Jitter may cause bit errors, and retransmission of data. Jitter can be defined as the variations of phase compared to an “ideal clock”, or as cycle to cycle jitter, irrespective of the “ideal” position of the signal edges. In both cases jitter is measured as either “peak-peak” or “rms”, meaning the standard deviation of the deviations.

What is wander?

Wander – Wander is slow beatings or irregularities in time. Wander variations occur over a period greater than 0.1s (10 Hz). Wander of the synchronization clock means that the clock is out of phase, and is the main cause for synchronization problems in the transport networks. Wander, which only partly can be filtered out in the network nodes, accumulates in the network and may even cause a total loss of synchronization. Incorrect synchronization in transport networks may cause severe transmission problems. Voice calls (fixed or cellular) will be lost, fax machines will misprint, and data will be lost or frequently re-transmitted. The network operator may lose customers (=money).