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First-Hand:War-Time Production and Design at Wheeler Labs, Mine Detection and IFF Radar

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Submitted by Harold Alden Wheeler

Then came World War II (1941-45) and the military requirements superseded the broadcast manufacturing. Starting just before United States declared war, we undertook a few small projects for the Signal Corps, none of which went into service. Then we were selected by a committee of NDRC (National Defense Research Council) to develop a "mine detector" for buried metallic mines. I was put in charge of this project and it became one of my specialties for a few years.

Under the committee's guidance, we built on the idea of an exploring coil that was used for "treasure finders." I invented a feature of concentric coils which made that idea practical. Our first complete design was flown to North Africa in time for the Allied invasion. It was used to clear buried mines ahead of a column of advancing tanks. Our design was manufactured by another company selected by the Signal Corps in a phony competition. It was designated the SCR-625 and hundreds were used by the Allied forces.

At the same time, we were introduced to radar by the Signal Corps at Fort Monmouth, New Jersey. They engaged our company to design some equipment for a new system which was an adjunct to the latest tracking radar. It was the IFF (Identity Friend or Foe) invented in Great Britain. They had negotiated for U.S. to assume the responsibility for production design and large-scale manufacture. It was extremely urgent. We made preliminary designs for all components and delivered them to the Signal Corps. The Army and Navy "weren't speaking to each other" so the Navy came to us separately.

The Mark III IFF system comprised an "interrogator-responsor" (IR) associated with a tracking radar, and a "transponder" on every aircraft or ship that might be a target. The IR was an adjunct to the tracking radar. It transmitted and received a pulse in synchronism with the radar pulse. The transponder received this transmitted pulse and responded with a coded pulse that was displayed on the radar screen beside the pulse reflected from the target.

The British circuit for the transponder was an Armstrong superregenerative pulse receiver. This served also as a transmitter of the coded reply pulse. This pulse was displayed on the radar scope beside the echo pulse to identify a friendly target (so don't shoot). I had to develop the first complete theory of superregeneration, so we could make valid tests.

The Mark III IFF was in the highest frequency band we had experienced (VHF 157- 187 MHz). This required new types of antennas and transmission-line circuits, so these also became my next specialty. One was a vertical monopole, dubbed the "life-saver" antenna in view of its wheel base, which was carried by every Allied surface vessel. It carried a tuned circuit in the base for impedance matching with a 50-ohm line over the wide frequency band. One "line stretcher" I designed was a strip between dielectric slabs between shield planes, a forerunner of the printed strip lines that were to become common after the war.

A by-product of the Mark III IFF was the first transponder beacon to be used as a landing aid for aircraft. In the air war over the Pacific, many of our aircraft had to land on the Aleutian Islands, which had very low visibility, so many were lost. We received an extremely urgent order to develop and deliver the "YH beacon" based on the Mark III transponder for use on landing strips on the Aleutians. The first complete unit was delivered with our design engineer for immediate installation. It revolutionized the practices of aircraft rendezvous and landing. We contracted for the manufacture and delivery of many units for installation at Army airfields. I enjoyed the privilege of working with the Wheeler Laboratory group of young engineers which were a carry-over from my company. As president of Wheeler Labs, I was in management but I was largely relieved of the problems of management by our contractors and my staff.

In general, I enjoyed much freedom and remarkable appreciation of my work. I was mostly self-propelled, beyond the call of duty, because I enjoyed my work. It was a challenge to respond to my opportunities and to keep up with my ambitious and talented staff. I sometimes wonder if I should have provided them with more direct encouragement and freedom. In retrospect, I find myself more critical of my deficiencies than those of my superiors and subordinates. In Wheeler Laboratories, of course, my only "superiors" were the groups who were steering our work to meet their objectives. There my experience was very gratifying.

Before the war, we never had time cards. Later generations of engineers cannot imagine the freedom we used to enjoy in my company. It was not so in the larger companies, especially in the telephone company that was subject to regulation.

There were few occasions when my proposals were not welcomed, usually for sound reasons. My more vivid recollections relate to the few occasions when I rejected a sound proposal by a member of my staff. In such cases, I tended to be short-sighted, not appreciating the opportunities that should be expected with progress.

I joined IRE in 1927 (at age twenty-four) as soon as I became aware of it. Professor Hazeltine was one of the leading members of IRE at the time and our Chief Engineer was a member. However, they did not urge me to join as soon as I should have. In college, my professors had leaned towards the American Physical Society since I was involved in the physics curriculum.

Later I joined the older society, AlEE (American Institute of Electrical Engineers, established 1884) which in 1964 was merged with IRE to form IEEE.

Before World War II, the IRE grew at a healthy but not spectacular rate. It was fun. I attended most of the conventions and was acquainted with most of the leaders. Then, all topics were basically covered in Proceedings.

After the war, all that changed. The explosive growth led to more reliance on local sections. Publications had to be separated by Professional Groups (now Societies). Then the merger with AlEE further enlarged the bureaucracy.

Big is not beautiful. My local Section (Santa Barbara, CA) has nearly one thousand members but the attendance at a typical Section meeting is only thirty (three percent). In the United States, I suspect that only one half of the eligible engineering graduates are joining IEEE. With all the Society Transactions, there is insufficient space for all the papers submit, even after condensed. I query whether the rate of growth of IEEE can continue, or even whether I want it to. Mostly I like its activities but I feel "lost in the shuffle."