Fundamental Measurement Techniques: Signal Generation
Part three of our new occasional series around ‘fundamental measurement techniques’ takes a look at the basics of signal generation.
We will review the basics of signal and modulation type.
It is worth re-iterating that we are looking at the basics and not state of the art measurements. If the basic measurement is performed and understood correctly then similar advances and adaptations can be achieved.
In any case many signal generators of varying complexity of measurement capability are available from MCS Test Equipment.
So what are the basic needs for creating test signals? They are everywhere, communications, cinema, defence, surveillance, manufacturing and R&D. Everywhere.
Signals can be generated as pure or modulated.
The sine wave is the basic, non-modulated signal. It is useful for stimulus/response testing of linear components.
Modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted.
- Important Characteristics for Amplitude Modulation include Modulation frequency (rate), Depth of modulation (Mod Index), Linear AM (%), Log AM (dB), Sensitivity (depth/volt), Distortion %.
- Important measurements include Amplitude, Voltage, Time, Carrier
- Important Characteristics for Frequency Modulation include Frequency Deviation and Modulation Frequency.
- Important measurements include Accuracy, Resolution, Distortion, Sensitivity (dev/volt)
- Frequency modulated signals are common in FM Radio, Aviation Flight systems, Radar and many other applications
- Important Characteristics for Phase Modulation include Phase deviation, Modulation Rate, Accuracy, Resolution, Distortion, Sensitivity
- Phase Modulated signals are commonly used in Radar applications and communications.
- Important Characteristics for Pulse Modulation include Pulse width, Pulse period, On/Off ratio, Rise time
- Pulse Modulated signals are commonly used in Radar, High Power Stimulus/Response and Communications
In contrast to Analogue Modulation, Composite Modulation is the simultaneous modulation of two or more Modulation Types. Here Vector signals are measured using a polar display of amplitude and phase where magnitude is an absolute value and phase is relative to a reference signal (0 degrees).
Next time we’ll look at signal simulation.