SECRET WIRELESS.

Hawera Star, Volume XLV, 10 December 1925, Page 8

SECRET WIRELESS.

AMERICAN INVESTOR'S CI/AJMS

NEW YORK, Nov. 15. A! demonstration of the simultaneous transmission of eight or more wireless messages from one transmitting valve on. the same ten metre wave length, jjptl their reception on a single instrument, was made .two weeks ago by the inventor, Mr. J. H. Hammond, jun., before officials of the Navy Department, who luave now permitted the announcement of a detailed account ol this system of “selective” secret radio transmission. Prime importance it attached to the utilisation of short wave lengths in view of Hie fact that virtually all the available wave lengths have already been allotted to broadcasting stations. Air. Hammond’s system permits the commercial utilisation of low wave* without disturbance from interferences.

The general principle ol the system is tlie projection of a short 'length carrier wave at the rate of, say, 30,000.000 vibrations per second, into which are impressed one or more “modulatory” waves at the rate ol’ 27 ,000 vibrations per second and upwards. These modulatory waves produce periodic changes of intensity in the carrier wave. The Hammond receiver i« designed to separate the frequencies of the complex incoming wave, having one circuit sensitive to the carrier wave and the other circuits .sensitive to the frequencies of the modulatory waves. Only an operator knowing the frequencies' which are being used can pick out i nooming messages.