The Invention of the K-55, SpeedGun, and Others

In another e-mail, the designer of the K-55 radar gun, Bob Patterson, wrote to me:


Please feel free to use this story any way you like. There is really a lot more detail but it’s probably not pertinent to the big picture.

When we formed MPH I wanted to call it Xecar (Seek car), but McCoy and Sergent quickly squelched that (bad) idea and suggested MPH ! I agreed quickly and had my old friend, Jose Conde, from my Vendo days, design the MPH logo, which, as far as I know, is still in use.

Some of the ideas for the K55 came from my experience in designing telephone EKG equipment for transmitting heart EKG’s to specialists. This was done with a 1300 Hz signal FM’d +/- 250 Hz. It worked well, till the phone line became noisy so I added a phase locked loop filter that worked so well that it would record when the signals were barely audible at all! Naturally, when the K-55 was rolling over in my mind, it became apparent that phase locked loops would play a major part. As it turned out, phase locked loops provided both the verification (validly) and was the basis for the tracking filter! The tracking filter alone was responsible for a 13 db signal to noise improvement.

The original choice of op amps turned out to be a problem, so comparators and better op amps with smaller offsets resolved that issue. Another goal of the K55 was to have real time subtraction. As it turned out this solved any perceived problem of closing speed and own speed not occurring , (ugh). Again, the double edge subtractor turned out to be the simplest solution, as well. The subtractor and the tracking filter was an original design. The verification phase locked loop is straight out of the RCA handbook. The fixed active filters underwent improvement as op amps and techniques improved.
By the time MPH went into business, several manufactures had Gunn oscillators. We used them all at one time or another.

It seemed that no one could produce a good consistent unit, so we hopped from one to another. I decided to see if we could build our own oscillator, so I contracted John Brassfield to do this, The Brassfield oscillator worked well, was small and low noise and had $8.00 in parts as opposed to a $34-$40 GE or Microwave Associates package. Getting consistent mixer diodes was always a problem, too. We’d go for months with no problems, then they would all go sour and the manufactures would just shrug!

An interesting sideline, early on, was GE’s insistence on testing my voltage regulator before guaranteeing their oscillators. The PNP low drop out regulator was original, too. That same circuit is used in my buddy’s cap tester and monitor test pattern generator, today. A slight mod on the circuit made it an electronic circuit breaker, protecting it from shorts and overloads. I sure could have used a cap tester when I was doing medical equipment. Early small electrolytics were not what they are today. One piece of medical equipment that we sold would be inspected for the presence of Cornell Dublier electrolytics, if any were present, they were replaced! The failure was almost always in ESR, not capacitance. I did have a problem with some IT&T tantalum caps that would explode! There were all red, and we advised that any red “bomb” be replaced.
All this brings back a lot of forgotten incidences…no wonder I ramble so badly…I’ll later tell you some of the K15 and S80 stories.

Bob Patterson