Tesla's Tuning Plan - It Assures Secrecy

An Advance in Wireless Telegraphy — Meddling Impossible.

Any one who has ever tried to persuade Mr. Tesla to talk for publication about his experiments and projects knows how firm and courteous are his refusals. Nevertheless, one source of information about his inventions is open to the public. His patents are matters of record. Any one may obtain copies by proceeding in the right manner, though familiarity with legal phraseology and electricity is necessary fully to understand them. Two patents, almost identical in tenor, were recently issued to Mr. Tesla. The invention which they cover seems to constitute a distinct improvement in wireless telegraphy, and its character and purpose are perfectly intelligible. 

Almost from the first it has been apparent that that system of communication would have a limited application unless secrecy could be insured. Hence, several of the most conspicuous workers in this field have been studying how to attain such a result. While their methods differ in detail, they all agree that the problem is to be solved by "tuning." By that phrase electricians mean a regulation or adjustment of the transmitter which makes it send out waves of a certain frequency — say 500,000 a second — and a treatment of the receiving apparatus which renders the latter more susceptible to that number than to any other. It has been assumed, rashly perhaps, that unless a piratically disposed outsider either knew what frequency was being used, or hit upon it by accident, he could not adjust his instruments so that he could steal a message where "tuning" had been employed. Of course, where no attempt was made to insure such agreement, wireless communications would not be private. In some kinds of service, indeed — as between steamships meeting at sea — no harm would result from overhearing.

In his patent specification Mr. Tesla points out a difficulty which is experienced in the operation just described, and which he has sought to evade. A phenomenon is observed in the generation of electric waves which, parallels one in music. If a given tone is produced by a violin string, several others, less audible, will also be emitted. If that tone be the one which is caused by one hundred vibrations a second, the additional but fainter sounds will be those resulting from 200, 300 and other frequencies. Such extra tones, or "harmonics," represent exact multiples of the number of vibrations requisite to the lowest, or fundamental, one, and there are usually six of them. When a Hertz wave generator is put in operation, that, too. produces "harmonics." Besides the one principal frequency which the operator aims to employ, his apparatus will also give out multiples. Mr. Tesla declares that a receiver which has been regulated to respond to one frequency is likely to pick up waves which are given off anywhere from exactly twice to exactly seven times as often. Hence it might receive messages not intended for that station. That system of tuning, therefore, seems less secure than is desirable.

Mr. Tesla's plan certainly appears distinctly superior to this. What he proposes to do is to generate two or more sets of waves at once, and employ them all simultaneously in sending. These might have frequencies proportioned to each other in some such fashion as 13 and 17, or 37 and 43, or 73, 80 and 101. Only a receiver which had been tuned to respond to two or three selected rates of vibration, when all were in use, would be able to pick up a message thus sent. It will be seen at a glance that this scheme differs from the other very much as the many notched Yale key differs from an ordinary latch key. Though Mr. Tesla thinks that only two frequencies would usually be enough, the system admits of considerable multiplicates. More- over, it may be taken for granted that the mechanism used would admit of a quick alteration of the selected frequencies, like that of the numbers of a combination for a bank safe lock.

Another advantage may result from this invention besides that of secrecy. It may avert mischievous interference. Some years ago, when preparations had been made for reporting the international yacht races off Sandy Hook, the following incident occurred: A press boat went down the Bay, a day or two in advance, to test its apparatus, and began sending messages to land. Persons on another boat, with similar apparatus, sent out signals at the same moment. In consequence, there was a confusing jumble of letters at the receiving station. One message overlapped the other. A few weeks ago, while Dr. Fleming was giving a lecture in London to prove how beautifully the Marconi "tuning" system worked, Nevil Maskelyne sent in "Rats!" and other inappropriate remarks from a point outside, and the speaker's instruments recorded them, much to his embarrassment.

Only last week Dr. Slaby, the author of one of the German systems of wireless telegraphy, openly avowed his belief in the propriety of interfering with the receipt of Marconi messages in England by sending out a continuous stream of signals with a powerful transmitter on the German coast. Finally, it is interesting to speculate for about ten seconds as to what would happen at Cape Cod if, while Marconi was trying to send thither from Poldhu, Mr. Tesla were to start up his generators at Wardenclyffe. The South Wellfleet receiving operator's hair would probably turn gray with perplexity in the effort to decipher the communications that actuated his instruments.

Quite aside from the morality of such conduct (which might depend on circumstances not known to the public), it seems to be entirely feasible. Apparently, too, a receiver which has been adjusted to respond to Mr. Tesla's combination would be immune against any amount of outside interference. Time only can tell the full value of his latest patents, but an unprejudiced judge can easily see immense possibilities in the idea.