There's an excellent article about load coils and bridge taps, provided by USMILSCOM, at
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Neal McLain
***** Moderator's Note *****My first introduction to loading coils was as a ham radio operator: we used them to make the "Terminal Units" that converted radio signals into the Baudot code used by Model 15 teletypes. The TU's were modems, made with two audio filters, one each for mark and space signals.
This was, of course, before the computer age: making a filter for 2975 Hz required a _lot_ of inductance, and 88 mh toroids filled the bill.
Bill Horne Temporary Moderator