[Milsurplus] inductive loops

[Ralph Cameron]

HUE:

The inductive loop was actually tuned. We would wire the perimeter of a roof, such as a rubber company, in one instance, using no. 6 rubber covered wire. The loop could be several hundred feet long. 

The equipment was made by N.V.Nira of Holland and consisted of a couple of 12AT7s in a multivibrator acting as an oscillator and another one or two as isolation and amplifier. It was quite low powered, on the order of a watt or two. 

There were banks of high quality capacitors which were strapped into the circuit to provide a certain load to the final amp. My recollection is a bit sketchy but there were about ten frequencies ranging from about 10Khz - 30Khz. 

The signal was definitely NSS which I assumed incorrectly issued from Jim Creek. It sounded like mcw to me and endlessly sent "V-V-V de NSS, NSS,NSS" similar to a channel occupier.16Khz was the only frequency received and the receivers just had a built in ferrite antenna, much like today's pocket pagers. 

I installed a loop set up in George's Spaghetti House in downtown Toronto and the cooks used it to page the waiters/waitresses when the stuff was ready. The waiters carried paging receivers that had an illuminated light that lit up so patrons weren't disturbed. Of course, using bakelite PCB construction in a hot and humid kitchen caused many outages and to work in there on a saturday night was hell on earth, but interesting. 

Ralph 
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