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Analog Demodulation X-Series Measurement Application N9063A & W9063A

Technical Overviews

Introduction

  • Demodulate AM, FM, or PM
  • Quad view, simultaneously displays RF spectrum, demodulated waveform, AF spectrum, demod metrics, and transient events such as attack/release time
  • Analyze FM stereo signals for MPX, mono, stereo, channel characterization, and RDS/RBDS decoding
  • Most complete set of post-demod filters
  • Speaker out (tune and listen) and analog output
  • Smooth migration from 8901A/B modulation analyzers

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:

  • Radio transmitter tests
  • Signal generator calibration
  • FM stereo transmitter tests
  • HP/Keysight 8901A/B replacement
  • Incidental modulation analysis (such as AM to PM, AM to FM, etc.)
  • Transient events and signal settling time analysis

Analog Demodulation Measurements

With the analog demodulation measurement application, you can perform analog modulation analysis on various radio transmitting devices. The analysis includes:

  • RF spectrum of the modulated signal
  • Demod waveform (time-domain view of the baseband signal). FM stereo can view MPX, mono, stereo, left or right demod waveforms.
  • AF spectrum (i.e., frequency-domain view of the baseband signal). FM stereo can view MPX, mono, stereo, left or right AF spectrum.
  • Modulation metrics
  • AM depth
  • FM deviation
  • Phase deviation
  • Carrier power
  • Carrier frequency error (FM and PM only)
  • Modulation rate
  • Distortion/total Vrms
  • Signal to noise and distortion ratio (SINAD)
  • Total harmonic distortion (THD)
  • Left to right ratio
  • Mono to stereo ratio
  • 38 kHz pilot frequency error and phase error
  • RDS/RBDS decoding (including  BLER, basic tuning and switching info, radio text, program item number and slow labeling codes, clock time, and date)

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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