The transmitting station SAQ in Sweden regularly puts their big transmitter on the air at 17 kHz. The "transmitter" is an Alexanderson Alternator - a fascinating mechanical beast that did an excellent job generating pure CW back in the days when most stations were running spark. Google will turn up a wealth of information and photos of it.
Of course electromagnetic waves are not sound waves. You can't hear them with only your ears even at such low frequencies. Back in the early days of "radio" the consensus among the experts was that the longer the wavelength (the lower the frequency) the longer the range, so much effort was put into very low frequency systems that operated in the same frequency range in which we hear sounds. And electromagnetic waves at those frequencies do penetrate earth and water better (Navies still use them to communicate with submerged submarines). It was that flawed thinking that got us Hams pushed onto the "useless" Short Wave bands were the experts were certain we'd never "get out of our own backyards" running only a kilowatt or less. Ron AC7AC -----Original Message----- The receiving setup is a large 4' diameter loop of many turns (maybe 30-50) of copper wire (salvaged from old transformers) connected to a diode detector and high gain audio amplifier. Essentially an audio frequency crystal set followed by a high gain audio amplifier. I hung the loop vertically in the attic. It was possible to hear "whistlers" from storm centers long before you could hear the thunder. Whistlers appear to be electromagnetic waves that fall within the the audio frequency spectrum, but they cannot be detected directly by the ear. Back to Elecraft topics hi Jim VE3CI ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
