Data Communication Equipment and Tests

This page covers data communication equipment used for testing, and dives into the common tests performed. We’ll look at pattern generators, BER (Bit Error Rate) testers, TDR testers (also known as LAN meters or cable analyzers), protocol analyzers, and more. We’ll also cover tests like eye diagrams, noise margin analysis, and BER/PER measurements.

Introduction

Modern wireless communication technologies like LTE, LTE-Advanced, and 5G are pushing the boundaries due to complex data modulation techniques. While standard RF and wireless equipment suffice for basic modulation schemes (ASK, FSK, PSK), more advanced techniques require in-depth analysis of binary signals to truly understand their behavior.

Baseband Data Signals

Data Communication Tests

Here’s a rundown of common data communication tests used to verify devices:

Eye Diagrams

Eye diagrams are a common method for analyzing the quality of binary data. They’re created by overlapping individual bits on top of one another. The resulting signal resembles an open “eye.” The shape of this pattern, and how open the eye is, directly correlates with the transmission quality.

Figure 1 (not included here, see baseband signal image above) depicts baseband data signals traveling through a medium like coaxial or twisted-pair cable.

Figure 2 (see eye diagram image below) illustrates eye diagrams for signals with good bandwidth, limited bandwidth, and severely limited bandwidth with noise. Notice the varying amplitude of the signals due to different noise levels along the transmission path.

Noise Margin

Noise margin is expressed as a percentage, calculated by dividing the noise margin level ‘a’ by the maximum peak-to-peak value of the eye ‘A’. A smaller noise margin indicates higher noise and a greater Bit Error Rate (BER).

Noise margin = (a/A) x 100

Bit Error Rate (BER)

This test compares transmitted bits with received bits. It tracks the total number of bits transmitted and the number of bits received in error. It’s calculated as follows:

BER (%) = (Number of bits received in error / total number of bits transmitted) x 100

Eye Diagrams

Data Communication Equipments

Let’s explore the key equipment used for data communication testing:

Pattern Generator

A pattern generator produces fixed binary bit patterns in serial form. It serves as a test signal generator. It can generate repeating ASCII code or any desired binary stream of 1s and 0s. These generators are available as dedicated equipment, or they can be simulated in software for testing purposes.

Oscilloscope

The oscilloscope is a time-domain instrument used to analyze the time-domain behavior of binary signals, including the creation and analysis of eye diagrams.

BER Tester

This tool measures the Bit Error Rate (BER) of a communication chain, both standalone and end-to-end, providing a vital metric of system performance.

TDR Tester

Also known as a cable analyzer or LAN analyzer, this equipment connects to coaxial or twisted-pair cables for testing and measurement. TDR stands for Time Domain Reflectometry.

Some of the tests performed by a TDR analyzer include:

• Open circuit test
• Short circuit test
• Impedance anomalies on cables (coaxial, twisted pair)
• Cable length measurement
• Capacitance measurement
• Loop resistance measurement
• Cable attenuation measurement
• Cable miswiring

Protocol Analyzer

A protocol analyzer captures and analyzes data transmitted in real-time without disrupting the normal functioning of the communication chain or system.

Data communication systems transmit data in specific packet and/or frame formats. This includes sync bits, source/destination addresses, headers, error correction bytes, the payload, and more. The protocol analyzer segregates all these frame/packet information fields and displays them, making analysis possible.

Protocol analyzers are used to examine data communication protocols such as HDLC, SDLC, BISYNC, Ethernet, SONET, etc.