The 704 remains locked in the cable industry’s memory.

Stewart SchleyFor devotees of Apple, the Macintosh computer stands out as the breakthrough invention that changed the world and defined the company. For AT&T – the old AT&T – a switchboard for routing calls represents the iconic image of a communications revolution. And in television, NBC’s peacock signified a breathtaking leap forward into a new era of color images.

In cable, the cable modem and the television converter loom large as signatures of technological advancement. But industry historians point to a far less notorious device as the innovation that propelled the industry from its tenuous origins to an echelon reserved for the truly game-changing. It was a signal meter.

Specifically, the long-lived Jerrold Electronics 704 Field Strength Meter, a measurement tool so essential to cable’s early growth that an industry fraternal organization, The Loyal Order of the 704, is organized around the product’s identifying part number.

The significance of the Jerrold 704 is rooted in the fundamental engineering challenge that confronted the barely born U.S. cable industry in the early 1950s, when the founder of Jerrold Electronics, Milton Shapp, made a bet that there was a business to be made out of supplying components to the scrappy collective of entrepreneurs who were building cable systems in rural America.

The challenge involved getting acceptable television signals to appear on TV sets located miles away from signal origination points. The prevailing architecture, insisted on by Shapp’s engineering and installation teams, depended on a cascade of booster amplifiers placed along a transmission cable to elevate signal strength that inevitably faded as a function of distance. Knowing whether the signal was adequate at any given point was essential. The alternative was to find only at the point of a customer installation that reception was either suitable or poor.

A portable field meter could solve the problem by providing technicians with a handy way to measure signal quality along the cascade without actually having to view pictures on a TV set. In 1951, the Jerrold inventor, Ken Simons, began working to adapt attributes of an RCA low-frequency meter for use in a cable TV environment. Simons, a former RCA engineer, knew that cable installers needed a highly dependable device that could be calibrated quickly to tune to the frequencies used by cable transmission systems. On an educated hunch, he insisted on accommodating mid-band frequencies, which were not then used for cable channels but might have been in the future. The 704 also was ambidextrous: It measured not just signal strength, but field intensity of broadcast signals, for help in determining antenna locations.

Simons’ original mock-up was hardly aesthetic. In an oral history interview conducted for The Cable Center before his death in 2004, Simons noted the original prototype used a fabric strap to cradle a 6-volt battery. “I had built the 704, the original prototype model, with the sheet copper chassis, rather badly bent. I didn't even have a metal-bending brake. It was bent with pliers, it used a Dumont tuner and it was battery-operated; it had a vibrator power supply with a 6-volt battery, regular size storage battery, which was slung underneath with a webbing strap. You could hardly lift the whole affair, but it worked,” Simons said.

But Jerrold’s product design group refashioned the assemblage into a sturdy, rectangular unit technicians could tote by gripping an attached strap.

It’s a testament to Jerrold’s foresight that the 704 remained in use for more than 20 years until it finally was supplanted by a successor meter. In that time, the cable industry grew from a smallish afterthought in the U.S. telecommunications market into a competitor meaningful enough to attract the attention – and the opposition – of powerful interests in broadcasting and telephony.

Unlike the TV channel converter that came to symbolize the presence of “cable TV” in a customer home, Jerrold’s 704 was invisible to the consumer market. In its entire history, only about 8,000 units were sold. But that was enough to propel a young industry past its toddler era into an economic adolescence.

Behind the scenes, and with every calibration, the 704 came to represent the cable industry’s determination to become something bigger. A generation of engineers grew up with the device. And although the 704 field strength meter would never be featured in an iconic TV commercial, like Apple’s Macintosh, it remains locked in the cable industry’s memory with a reverence that’s just as enduring.