Wednesday, April 13, 2011

Bels and Nepers - BSTJ 1929

Today's ARRL Contest Update mentions the on-line availability of all the issues of the Bell System Technical Journal. That's a wonderful thing, because so much of the cutting edge electronic and technical developments of the era 1922-1983 were written up there.  It is a spectacular testament to the value of AT&T's Bell Laboratories.  It is so sad that Bell Labs (and other private research labs like IBM's) no longer have the prominence in fundamental research they once did.

So anyway, enough sentimentality.  I thought I would open up a BSTJ article at random.  Sure enough, it was very interesting.  The first article in the Jan., 1929, issue was Decibel--The Name for the Transmission Unit, by W.H. Martin, wherein the "db" was introduced to the technical public!

Why do we always use "db" instead of bels? AT&T had been using the "transmission unit" for some time, which indicated a ratio of 10**0.1 -- which was identical to the new decibel.  It's a handy unit, too, because it is just about the minimum loudness ratio a person can detect in favorable conditions.

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