The 704 Jerrold Field Strength Meter

Workhorse to Icon

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 704B continued until 1967 or so, when it was phased out in favor of the Jerrold 727 meter, which was lighter, rechargeable battery operated, and could be supplied with a plug-in adapter to tune the superband frequencies then coming into use. The pioneering engineers building cable plant determined early that amplifier signal levels had to be controlled accurately, and a reliable, field portable, signal strength meter was going to be key. In 1950, Milt 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.

Today, the 704 is an icon representing the technical efforts upon which today’s broadband business was built.  For a number of seasoned cable folks, a venerable 704 meter is now a proud possession and reminder of their history. Cable engineers will not soon forget the fundamental RF nature of the signals delivered to cable subscribers, and the continuing need to make accurate measurements of RF signal levels.   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

Ken Simons

Staring in the 1930, Ken Simons worked for a number of years for RCA, with a stint as an engineer for WCAU. About 1950 Ken 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. On his return to Philadelphia a year later, he started working for Milton J. Shapp, the founder of Jerrold, 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 says that he actually built a field strength meter in 1940 while working for RCA. It was supposed to be truck portable. A standard 9 inch TV receiver, then called a TRK-9, with a 110 volt power supply, was used. The whole arrangement was mounted in two boxes. On the top of the receiver box there was a meter to measure the voltage across the video detector.  Although it wasn’t calibrated in micro-volts, Simons says that this was his first field strength meter design.

For field use, there was obvious need for a small and portable device for measuring signal levels. So one of his Simons first projects, working for Shapp, was to design a field strength meter.  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, although it was pretty well in the future. It was almost inevitable the midband would show up. So any kind of a switched tuner was out of the question. So he determined that the Mallory Inductuner as was the best basis for a field strength meter because (a) you could tune it to any frequency you like and (b) it was good electrically. Simons still regards the Mallory Inductuner as an amazing job of design. 

Simons wanted to build an instrument that was dependable, covered the frequency range, but also it had to be calibratable. In an 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 calibration. Simons 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.

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.

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 recollection is 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. 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. Prior to joining the institute, Arbeiter had served in the US Army from 1942 to 1945, spending time in Europe with the radio division of the Tactical Air Command. 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. Simons recounts that he will never forget the condition in which I took it down to Hank Arbeiter at the location on North Sixth Street, in Philadelphia.  In a back room there were four girls putting things together; in the front room there was a secretary and Milt Shapp, and in the side room there was Hank Arbeiter and his engineering department.

A prototype, clad in roofing copper, was what Simons gave to Hank Arbeiter and this is where the 704 came from. What Simons gave Arbeiter was essentially the schematic and a working lash-up; Arbeiter did everything else. 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!

Hank Arbeiter died in 1986. His sister-in-law, Jean Douglass and her husband Ralph Douglass continue today the family involvement in the cable industry with PECA Incorporated, providing engineering, prototyping and manufacturing services to the industry since 1967.

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