Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Parpp807-at-aol-dot-com> Hi Bert , The only reference is the one given in the article: Goldsmith, Alfred N., Radio Telephony, The Wireless Press, NY, 1918. I'll get back on the Glowbugs reflector to see if any more info is available. Regards, Ralph