Historical article:
STARS CONTROL WAVE-LENGTH;
USED TO CHECK TUNING FORK
An interesting development in checking the frequencies of broadcasting stations is announced by the A.W.A. Research Laboratory
THE stars in the heavens have been harnessed to prevent overlapping among broadcasting stations. By their aid, complaints of interference between any of the 121 stations in Australia have been practically eliminated.
To test whether a station is on its wave-length, the scientific staff at the A.W.A. Research Laboratory, Ashfield, employs a tuning fork of high-grade Elinvar steel. This fork, when vibrating, has a natural frequency of 1000 cycles per second, and when its frequency is compared with the frequency of a broadcast station or control equipment in course of manufacture, the slightest variation from an allotted frequency or wave-length is detected.
The paramount consideration regarding the tuning fork, therefore, is either that it must be correct, or, if it is not absolutely correct, that its degree of error should be known to a very precise figure.
Here is where the stars are invoked.
First, the fork must be kept at a very precise temperature and pressure. This is accomplished by enclosing it in a sealed metal cylinder around which are wound automatically-controlled heating elements. At the set temperature, the fork’s natural frequency is theoretically exactly 1000 cycles, although actually it might be 999,999 cycles. When vibrated, its pulsations are recorded on a tape. Parallel with this graph another record is made of time signals astronomically controlled, and received by wireless from the great observatories of the world. Any minute deviation of the tuning fork’s Impulses with those of sidereal time can be measured at leisure, so that the precise error—if any—of the tuning fork at any particular moment is known. The fork thus becomes an infallible measure, and so can reveal any divergence from accuracy on the part of a station under test. In this way, the A. W. A. laboratory is in a position to place any station on its frequency within a minute tolerance.
Note: A.W.A. is the “Amalgamated Wireless Australasia Ltd”.
