Workhorse to Icon
The 704 Jerrold Field Strength Meter
By Graham Stubbs, Principal, Graham Stubbs Associates
The 704B Jerrold Field Strength Meter
The history of the Jerrold 704 Field Strength Meter spans practically the entire life of the cable television industry. Conceived in 1951, shortly after the original seeds of the industry were planted in 1948-50 in Oregon, Arkansas and Pennsylvania, the 704 became the workhorse of the industry and remained so until the 1970’s. Manufacturing of the 704 started in 1953 and continued until 1967 or so, when it was phased out in favor of the Jerrold 727 meter. During the manufacturing run of the 704/A/B meters, more than eight thousand were produced.
Today, the 704 is regarded as an icon, representing the engineers and technicians, upon whose technical accomplishments today’s broadband business was built. The 704 model name survives in the name of the Loyal Order of the 704, an industry group of engineers with long memories… and tall stories.
The people behind the 704 In 1950, Milton Jerrold Shapp’s company Jerrold Electronics Corp., which had been supplying signal boosters for TV showrooms and apartment buildings, began to supply modified signal boosters to be used in cascaded cable systems. Shapp instituted a policy of having Jerrold engineers design systems and install the equipment. The critical need for accurate measurement of signal strength would have been driven home to the Jerrold engineers responsible for field operations. Milt Shapp had assembled an outstanding engineering team for Jerrold Electronics. The technical staff covered the whole gamut from original R&D, to product design for quantity production, to field operations.
Ken Simons Starting in the 1930, Ken Simons worked for a number of years for RCA, with a stint as station engineer for WCAU. About 1950 Simons had been talked into going from his home, in the Philadelphia suburbs, to Buffalo, NY, to work for Colonial Radio (Sylvania). He worked there in advanced development, and one of his assignments was evaluating tuners. Among other tuners that he checked was the Dumont Inductuner, which used a Mallory design. Upon his return to Philadelphia a year later, he started working for Milt Shapp as a consulting engineer. One of his first assignments was to address the need for a piece of equipment with which to make reliable measurements of signal levels
Simons was certain that, in the long run, cable was not going to be satisfied with just the two VHF bands–low band and high band. It was almost inevitable the midband would show up, although it was pretty well in the future. Any kind of a switched tuner was out of the question. He determined that the Mallory Inductuner was the best basis for a field strength meter because (a) it could tune continuously to any frequency within its range (b) it was good electrically. Simons wanted to build an instrument that was dependable, covered the frequency range, but also it had to be calibratable
In his earlier job, as general engineer for WCAU, one of Simons’ tasks was measuring field strength, and he had experience with an RCA low frequency field strength meter, which used an oscillator with a standard output level for calibration. He didn’t want to go to that expense so he made his circuits mechanically very stable and also all of the gain controlling was done defined by tremendous DC feedback in the tube cathode circuits. For best linearity, Simons went with a high level detector circuit DC current was very stable, regardless of line voltage, and as a result, the 704 was very dependable.
Mike Jeffers with an original 704, circa 1950s.
An early member of the technical team was Mike Jeffers, who went on to a long and distinguished career with Jerrold and its successor G.I. A young Mike Jeffers is seen here (right, holding the antenna) in an illustration to a 1959 Jerrold publication, with an original 704 in the foreground.
Simons worked on projects for Shapp in his laboratory near his home in Bryn Athyn, PA. Caywood Cooley, another employee of Jerrold, had been brought in to supervise field installation of Jerrold gear, and from time to time he was at the Bryn Athyn lab.
In 2001, Simons wrote about the 704 project: “One day Caywood Cooley came into the Bryn Athyn lab with a Philco television receiver which he had modified. He had connected a DC meter to the video detector so that he could measure signal strength on a cable system. The lights came on and the bells started ringing! I knew that viewing the picture was not essential. A smaller, lighter unit, designed only to measure the strength of the carriers would be very useful. Thus the 704 Field-Strength meter was born!
Fortunately, part of my former job at Sylvania had been to evaluate various makes of TV tuners. I knew that I like the Mallory Inductuner, as used by Dumont. This unit tuned continuously from channel 2 to channel 13, using a sliding contact which progressively shorted out turns on a spirally wound inductor. This idea doesn’t sound practical. One always expects trouble with movable electrical contacts. The Inductuner did, however, work beautifully. Although several thousands instruments were built, I don’t know of any problems due to the use of this tuner.
After the tuner, the rest of the design was quite straightforward. There were three IF stages, a detector, and a DC amplifier to drive the meter. Gain was set to calibrated points by variable resistors in the cathode circuit of each IF amplifier tube. The supply voltage was held at 150 volts by a VR150 gas discharge tube. My notebook shows only ten entries relating to the Field Strength meter, so I suspect there were no major design problems.
It’s a shame that we don’t have a time machine. I would love to be able to show off the 704 as I delivered it to Arbeiter. The tuner assembly was mounted on roofing copper, with no proper right-angle bends. The unit was powered by a storage battery, which was slung underneath, being held by a cloth strap. It’s a tribute to Henry’s ability that he redesigned this into a neat-looking, producible unit.”
A vibrator power supply with a 6-volt regular size storage battery was slung underneath his prototype with a webbing strap. It was heavy, but the whole affair worked. Simons’ laboratory notebook places his design work on the prototype 704 between November 1951 and April 1952. Simons’ recollection was that that it took less than three years to design and get the 704 into production, which commenced in 1953.
Generations of cable engineers are familiar with Ken Simons name, having been brought up on the Simons “Technical handbook for CATV Systems” published by Jerrold Electronics Corp. Simons passed away in May, 2004. At age 90, still active in electronics R&D, Ken Simons was the honored guest at the June 2003 meeting of the Loyal Order of the 704 at SCTE EXPO in Philadelphia.
Hank Arbeiter
Jerrold’s first employee was Hank Arbeiter, who was hired by Milt Shapp from a job as an instructor at the television training Institute in Philadelphia. Arbeiter’s expertise was to make products into a reproducible form, that could pass muster in the field, and that could be maintained by customers.
It was to Arbeiter that Simons took his prototype field strength meter to turn it into a product. What Simons gave Arbeiter was essentially the schematic and a working lash-up; Arbeiter did everything else. He did the production design of most of Jerrold’s test equipment, including the famous sweep generators
Arbeiter’s wartime radio equipment experience in the service may have played a part in his choice of a mechanical design. One of the best-known pieces of radio test gear during WWII was the BC221 frequency meter, used for frequency calibration of radio receivers. The housing was a vertical cabinet, with a horizontal divider shelf. The heterodyne crystal frequency meter was located in the upper half, and a battery pack or a power supply in the lower half. A hinged cover protected the panel and controls; on the back of the hinged cover were calibration charts. Looking back on it, it doesn’t seem a huge leap to the familiar 704 design!
Arbeiter continued at Jerrold until his retirement in 1985 ; he did the production design of most of Jerrold’s test equipment, including the famous sweep generators. Hank Arbeiter died in 1986.
Why Field Strength Meter
Although an obvious application was measurement of signal levels in cable plant, it should be remembered that selection of receive antenna sites and installation of antennas were important parts of the cable engineer’s job. The 704B manual provides details of dipole antenna construction, and the use of the 704B as a field intensity meter. Hence the name Field Strength Meter rather than just signal strength meter..
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Graham,
You alluded to a picture of Mike Jeffer’s holding an antenna, with a 704 meter in the foreground. I have that picture in my office, although it wasn’t attached to you story. Can you tell me who the other person in the picture is, using the 704?
Thanks,
John Martin