Technical Overviews
Introduction
Analog Demodulation Measurement Application
Available on all Keysight Technologies, Inc. X-Series signal analyzers, the analog demodulation measurement application transforms the X-Series into an easy-to-use transmitter tester for analog modulated signals, including AM, FM, PM, and FM stereo. By adding fast, one-button measurements, the analog demodulation measurement application helps you design, evaluate, and manufacture your analog devices quickly and accurately. Even in the modern digital world, the analog demodulation measurement application helps you to troubleshoot distortions due to unintentional, analog modulation from digitally modulated transmitters—allowing you to stay on the leading edge of your design and manufacturing challenges.
The analog demodulation measurement application is just one in a common library of more than 25 measurement applications in the Keysight X-Series, an evolutionary approach to signal analysis that spans instrumentation, measurements, and software. The X-Series analyzers, with upgradeable CPU, memory, solid-state drives, and I/O ports, enable you to keep your test assets current and extend instrument longevity. Proven algorithms, 100% code-compatibility, and a common UI across the X-Series create a consistent measurement framework for signal analysis that ensures repeatable results and measurement integrity so you can leverage your test system software through all phases of product development. In addition to fixed, perpetual licenses for our X-Series measurement applications, we also offer transportable licenses which can increase the value of your investment by allowing to you transport the application to multiple X-Series instruments.
Analog Modulation and Demodulation Overview
Modulation is the process of translating some low-frequency or baseband signal (such as voice, music, or data) to a higher frequency (carrier signal). The primary reasons for modulation include allowing the simultaneous transmission of two or more baseband signals by translating them to different frequencies, and to take advantage of the greater efficiency and smaller size of higher-frequency antennae.
Analog modulation is the most fundamental modulation method. In analog modulation, the variations to the carrier are applied continuously in response to the analog information signal. By definition, the analog signal is continuous in time and amplitude, as opposed to a digital or discrete signal.
A high-frequency carrier signal commonly has sinusoidal form. There are two properties of a carrier signal that can be altered: 1) the amplitude (A) and 2) the angular position. Thus, there are amplitude modulation (AM) and angle modulation. Angle modulation can be further characterized as either frequency modulation (FM) or phase modulation (PM).
FM stereo is an enhancement to FM that uses stereo multiplexing. An FM stereo signal carries stereophonic programs in which signals are transmitted for L (left) and R (right) audio channels. Radio data system (RDS) consists of the text information such as traffic, weather, and radio station information carried in the FM signals. This information can be displayed on the screen of the end-user's device. RBDS is the United States version of RDS.
Analog demodulation is a reverse process of the analog modulation. It offers quantitative assessments for analog modulation qualities. Analog demodulation is not only essential in testing FM or AM transmitters, but is also a powerful troubleshooting tool for analyzing unintentional signals from digitally modulated transmitters such as 2G/3G cellular phones, and wireless LAN and WiMAX™ devices. The FM demodulation measurement is also an excellent alternative for high-volume manufacturing of low-price digital wireless devices, such as Bluetooth®, where test throughput and manufacturing costs are critical.
The analog demodulation measurement application runs on the Keysight X-Series signal analyzers and provides fast, complete, and easy-to-use measurements of AM, FM, PM, or FM stereo/RDS signals.
The primary targeted markets and use cases for the analog demodulation measurement application include:
Analog Demodulation Measurements
With the analog demodulation measurement application, you can perform analog modulation analysis on various radio transmitting devices. The analysis includes:
Measurement details
RF spectrum of the modulated signal
This is the most traditional spectrum analyzer measurement viewing the modulated carrier signal power in frequency domain. Prior to being modulated, the signal power of a sinusoidal carrier concentrates at the carrier frequency. By contrast, modulation causes sidebands indicating the power redistribution over frequencies. The pattern of the sidebands depends upon the modulation format.
Demod waveform
This measurement retrieves the baseband signal from the modulated signal via the demodulation process, and displays the baseband signal in a pattern of modulation depth/deviation versus time. Since the modulation depth/deviation is directly proportional to the instantaneous amplitude of the baseband signal, the measurement result helps to intuitively evaluate the quality of the baseband signal.
AF spectrum
By applying the fast Fourier transform (FFT) to the baseband waveform, this measurement demonstrates the baseband signal behaviors in frequency domain graphically. The AF spectrum reveals the distortion of the baseband signal clearly just as the RF spectrum does for the RF signal.
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