Interesting story behind the MILES cable and MSP development if folks are interested.
It is very interesting. Tell me, please.
Well the early cable development is second hand as we weren't part of this, and likely transpired in the late 60s. The cable was originally developed to detect magnetic type intruders, personnel with weapons, tanks, cars, and vehicles which it did, but the developers noticed that it could detect magnetically "clean" intruders and realized this was due to the cable's magnetostrictive effect. They set about to enhance this feature using proprietary cable cores which became the MILES cable and develop a more sensitive signal processor/detector which became the MAID.
The MAID Signal Processor worked well but did have issues with false alarms, especially during storms, and a replacement development program was started. We got involved in 76~77 as a consultant, later hired and developed the algorithms and circuits, a colleague conceived the unique preamp idea discussed later. The requirements were difficult as the entire signal processor needed to fit in a 150mm cube, have built in batter backup, consume less than 50mw and pass full military requirements including conducted and radiated susceptibility. The program we had was known to Sandia Labs and a group of researchers from major universities working with a new algorithm based around a Adaptive Recursive Filter (ARF), they were also working on a program but we didn't initially know, and they were given all our reports and design details. If you've ever worked on USG programs you'll recognize this as we were supposed to fail and Sandia Labs would be the design of choice for the future production.
Early in the design we realized/discovered to achieve the enormous dynamic range required that by pushing the signal integration right up to the front end was the best possible architecture and this also compensated for the natural rate sensitivity of the magnetic sensor which was proportional to rate of change of the earth's magnetic field which is locally disturbed by a magnetic type intruder, and also by the rate of change of ground pressure due to the magnetostrictive cable effect. Since the cable impedance was very low, pushing an integrator to the input requires a very large feedback capacitance, we used a large wet-slug tantalum selected for low leakage. The amp inside the integrator was a low noise selected dual transistor from National and a selected low power op-amp, and overall called a Rate Compensated Preamp. The transistor was biased for optimum low frequency noise and the base bias current was allowed to flow thru the cable, this created a means to detect a cable disconnect, degradation or cut. BTW this push the integrator right upon the input signal was used decades later at RF/MW in the PolyPhase Mixer which is one reason why it has such good NF & DR. After the integrated signal various frequency bands were selected by active filters with various characteristics, and the energy within these bands and various ratios used to detect and classify target intrusions.
We sent some folks out to collect MILES cable data from various USG facilities around NA to get typical signatures for different terrains, nearby railroads, various aircraft flying end of runway, sonic booms, thunder storms, winds, frozen ground and so on, even setting up a special field site at our facility for long term recordings (false alarms).
Some false alarms did show up and always about 6am. The field had signs to Keep Out, so we set up a camera to be triggered by the alarm and discovered a guy walking his dog across one of the cables. Left him a friendly reminder, and no more alarms!! Local HS kids were hired to try and run, jump, crawl, pole vault, anything they could do to get past the cable, even showed them where the cables were buried and they couldn't defeat the system!!
We were informed about Sandia and the various university efforts based upon the Adaptive Recurrsive Filter just before our 1st field test at Eglan AFB, Florida during "Smoke Week". Sandia Labs showed up with a large Grumman van (like UPS uses), with a diesel generator running a VAX 11780 and a large Igloo size metal box, we had our little analog 150mm cube box, and a couple chart recorders!!!
When asked about the size and power requirements we were imposed with, Sandia folks said they'll shrink everything into a series of custom chips and such...sure!!!
We beat or equalled every test parameter during the test, most importantly the probability of detection and false alarm rates were much better overall and the Sandia/University folks were not happy!!
Later the 2nd test was conducted at Rome AFB in late January for the frozen ground tests, same result. Honestly believe the single most important reason we were successfully was the Rate Compensated Preamp, which was the integrator right at the front end. The system had 146dBV gain available and the ratio of various energy band levels acts as a dynamic AGC giving the system the best possible chance of detecting an intruder while keep the false alarm rate very low. The Sandia & Universities ARF was very clever, but without the advantages of our preamp, they were at a signal disadvantage right from the start.
Anyway, we equaled or beat the ARF in every measurement category with our little analog 150mm cube with the Rate Compensated Preamp, and later this system was selected for production and replaced the MAIDs in the field
Sorry for the long note, maybe the moderators want to move this, unless its OK with other folks.
Best,
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