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Agilent Technologies March 2000 Issue 20 U.S. Edition Agilent Technologies and Communications: Six Decades of Measurement Contributions Contents 3 Agilent Technologies and Communications: Six Decades of Measurement Contributions 4 The early days 5 Cable multiplex communications 6 Pulse-coded modulation 7 Logic test and the digital revolution 8 Datacom testing 9 Digital transmission testers 10 Broadband communications 11 Terrestrial microwave communications 13 Satellite communications 15 Mobile-radio communications 16 Modern wireless communications 17 LMDS in the last mile 18 Military communications 21 Environmental testing 22 Broadcast communications 24 Cable television 25 Lightwave communications 27 RF and microwave component design 30 General communications applications 31 General technology contributions 33 Superstars 36 Agilent’s products today 2 Agilent Technologies and communications Agilent Technologies and Communications: Six Decades of Measurement Contributions It can be reasonably argued that Agilent Technologies—which incor- porates the former test and mea- surement sector of Hewlett-Packard Company—has been making measurement contributions to the communications industry ever since Dave Packard and Bill Hewlett assembled their first product, an audio oscillator, in 1939 in a Palo Alto, California, garage. That product was the HP 200A audio oscillator, and its most famous sale was to the Walt Disney Company for use in making the movie Fantasia. But it also was used widely in the design of trans- mission components, including amplifiers, transformers, and fil- ters, for the twisted-pair wireline telephony systems of that era. With the outbreak of World War II, communications technology became the focus of intense R&D efforts as Bill Hewlett and Dave Packard. a strategy for winning the war. In this document, we’ll take a The results of those efforts revolu- journey through the development of tionized the world. Agilent, through 20th century communications and its HP heritage, has played a signifi- Agilent’s test and measurement cant and continuing role in the contributions. Although we discuss communications revolution, making technologies up to the end of the hundreds of test and measurement century, our focus is on the histori- contributions in nearly every sector cal achievements rather than pre- of the industry. sent-day trends. 3 The early days In the earliest analog telephone Proceedings of technology, open-wire telephone 1939, the oscilla- lines dominated the outside plant. tor caught the Then came twisted-pair wires attention of the bundled into underground cables. Chief Engineer at In the U.S., these formed the back- Walt Disney bone of the communications system Company, who well into the 1940s. Some of us still needed a number have images of telephone poles of audio sources along country roads, with multiple for sound effects cross-arms and dozens of green-glass in Fantasia. The insulators supporting open wires competing oscilla- that went on for hundreds of miles. tor of the day was The 200A audio oscillator was Hewlett-Packard’s first commercial success. The technology of communicating a “beat-frequency” in those days was heroic, and it oscillator that cost seemed that the only way to let ten times as much. Disney’s Chief a common 7.5 watt lamp bulb—into more people communicate was Engineer bought eight of the the cathode circuit of the oscillator through brute force design, by HP models. vacuum tube. adding more wires over head or more cables under ground. The clever circuitry of the 200A With the introduction of the 300A audio oscillator was the subject audio analyzer (ca. 1941), engineers Hewlett-Packard’s original audio of Bill Hewlett’s Electronic could analyze signal distortion in oscillator, used with the 400A Engineering thesis at Stanford the audio components used in tele- vacuum tube voltmeter (ca. 1941) University. In a slim document of phony. Testing was still in its early that boasted a 1 megacycle band- less than 20 pages, he presented days. One HP engineer recalled as width, allowed the characterization a circuitry that was the essence of a college student being assigned to of frequency-response parameters of simplicity. It used a tunable resis- arrive at the engineering lab early a variety of system components, tance-capacitance network to pro- in the morning to turn on the including amplifiers, transformers, vide the 180-degree feedback phase instrument so that its vacuum-tube filters, line-loading components, shift needed for oscillation; an inex- drift would stabilize for lab use later and switches. One of Hewlett and pensive tunable radio capacitor for in the day. Packard’s objectives was to provide the two ganged capacitors; switched “inexpensive quality,” and the audio resistors to achieve the tuning In the telecommunications infra- oscillator was a good example. range; and an innovative amplitude- structure, the underground wire-pair Originally advertised for $71.50 in stabilizing function made by insert- plant served local distribution needs the Institute of Radio Engineer’s ing a positive-coefficient resistance— for decades, and HP continued to introduce new test products to improve its efficiency. In 1959, the 302A wave analyzer (20 Hz – 50 kHz) brought powerful low-frequency (LF) spectrum analysis to component and signal design. This analyzer was just the second HP product with an all-transistor design—the first being 1958’s 721A power supply. In 1962, HP introduced the 3550A portable frequency response test set for installation qualification and troubleshooting of twisted pair cables. This product was followed by the 3555A telephone test set. These instruments were called Transmission Measuring Sets (TMS), distinguishing them from the famil- The 3550A frequency response test set could qualify and troubleshoot twisted-pair cables. iar Transmission Impairment Measuring Sets (TIMS) of today. 4 Agilent Technologies and communications Cable multiplex communications As the 1940s’ wireline technology the 3745A selective level measuring reached its limits, particularly in the set (ca. 1975) offered system engi- underground cabling of twisted pairs neers following the CCITT-standards of wires that served urban areas, precise measurements of FDM tele- new technology was needed. One phone equipment with as many as answer was to exploit the broadband 3600 channels. This 25 MHz super- carrying capacity of coaxial cable, heterodyne receiver measured down and as a result, AT&T’s research labs as low as -125 dBm with synthesizer rolled out their first cable multiplex precision. In 1978, the 90 MHz systems, the L-1 through L-5. 3747A selective level measuring set was targeted at the new genera- Cable multiplexing grouped dozens tion of 60 MHz cable that handled of individual telephone conversations 13,000 channels. together using a technology called frequency domain multiplex (FDM). The 312A wave analyzer and 313A tracking The 3586A/B/C selective level Each conversation occupied 3 kHz of oscillator were diagnostic tools for multi- meters followed in 1980 for FDM channel width and was spaced 1 kHz plexed cable. applications to 32.5 MHz. And com- from its neighbors. Twelve audio chan- panion 3336A/B/C synthesizer/level nels were single-sideband-modulated As cable multiplex technology generators teamed with the selective into a group; five groups were com- progressed, AT&T added more and level meter products to characterize bined to form a super group; and ten broader channels to their cables, transmission components for super groups were combined into a pushing the technology to its limits both North American and CCITT master group. The key to this technol- by installing an underground cable signal formats. ogy was perfect linearity in the ampli- system across the U.S. from New fication and all other circuitry. Slight York to Los Angeles. Cable systems non-linearities showed up as inter- also began to provide the broadband modulation, which resulted in degrad- links required between the 7000 ed background noise and cross-talk. telephone central offices around the country. The AT&T L-systems Amplitude flatness across the many ultimately reached 65 MHz per cable. multiplexed channels was measured over the 1.5 MHz band by HP’s 310A The 312A wave analyzer (ca. 1966) wave analyzer (ca. 1963). A wave was a powerful diagnostic tool for analyzer is essentially a calibrated multiplexed cable because it cov- superheterodyne receiver, and this ered the 18 MHz range, was fully one featured a selectable output programmable, and featured many bandwidth, which allowed the detect- user improvements such as automatic ed audio modulation to be measured. frequency control. Outside the U.S., 5 Pulse-coded modulation In a real sense, most of the spectac- Now AT&T developed their T-systems, HP’s digital instrumentation devel- ular communication technologies of with a hierarchy of data rates up to oped across a broad front to help the late 20th century were based on T-4 (274 Mbit/s), running over coaxial speed the digital revolution. The a simple analog-to-digital concept. cable. Similar standards were devel- 4940A transmission impairment In the 1960s, when it became eco- oped outside the U.S., where the measuring set (ca. 1974) met an nomically and technically feasible CCITT hierarchy packed 30 voice urgent need as telephone companies to digitize analog waveforms on a channels into a 2.048 Mbit stream. began widespread installation of massive scale, everything in com- data modems to send data over munications got better. Using a The digital data streams revolution- voice circuits. This TIMS was well-known sampling theory and an ized telephone voice quality. As designed to measure the analog 8-bit digital word to express ampli- transmission distances had parameters of wire lines that affect tude samples taken at 8 kHz, each increased, the analog signals were data transmission, and it was used 3 kHz audio voice bandwidth was subject to gradually increasing widely as a verification tool for line converted into a 64 kb/s digital data noise.

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