AUTOMATIC RELAYS

Evening Star, Issue 22460, 3 October 1936, Page 4

AUTOMATIC RELAYS

NEW YORK-PHILADELPHiA CIRCUIT Features of a new ultra-short-wave circuit between New York and Philadelphia are automatic relay stations, and the transmission of drawings, type mutter, handwriting, and other facsimile material, simultaneously with the operation of automatic typewriters and of telegraph keyboards. At tho demonstration on June 11, David Sarnoff, president of the R.C.A., said: “Having developed a technique of operation for the three-metre wavelengths, we find in that region a medium of transmission unlike anything we have ever known. . . . We can not only send messages in facsimile as fast as present equipment will allow, bub We can send two pictures simultaneously, and on tho same radio wave we can also add two automatic typewriter channels and a telegraph channel. Of course, this means we can do all those things in both directions at the same time. . . . If we were concerned only with communication on a word basis, we could with increased power and filter systems, operate enough automatic typewriters to carry a total of 12,000 words per minute in both directions between New York and Philadelphia. . . . Now that we have the circuit, we shall turn again to tho laboratory to find out how best to make use of it. Of course, radio wants its share of telegraphic traffic, but it looks also at tho much bulkier mail bags.” There are automatic repeater stations between New York and Philadelphia, at Now Brunswick, New Jersey, and Ar ney’s Mount, near Trenton, New Jersey,, because “ the range of threemetro radio waves is virtually limited to line-of-sight ”; each of these repeater stations has two different transmitting wavelengths, one for each direction, and the terminal stations each use a sending wavelength, making six wavelengths for the circuit. If the service were _ extended to another city, the same six wavelengths could be used again in the same sequence, because the line-of-sight limit would prevent interference. This is how the circuit works:—

“ When it is desired to make tho circuit ready for traffic, New York or Philadelphia starts up its transmitter and sends a certain musical note which the receiving circuits are pre-set to ‘ recognise.’ At the unattended receiver at New Brunswick the tone passes through electrical filters somewhat like a key passed through the tumblers of a lock. Electrical circuits ‘ accept ’ the tone, and relays are actuated, turning on the power for the ‘ south ’ transmitter, which, when in operation, passes the tone on by radio to the Arney’s Alount station. There the operation is repeated. When the tone signal reaches the Philadelphia station the transmitter at that city is also automatically turned on, and the tone starts on its return journey, back to New York. Operators in New York know that when the tone comes back to them from the ‘ north ’ transmitter at New Brunswick, the entire circuit is in full operation and heady for traffic. The constant presence of the tone keeps the relays closed, and the circuit in an operating condition. When the tone is withdrawn from tho circuit, relays click in tho same succession over tho round trip to Philadelphia, and one by one the transmitters are automatically turned off. Philadelphia has the same control over tho circuit as New York.” The new instruments are said to look strange. Aerials are called “Christmas Trees ” and “ Turnstiles ” ; parts of the receivers look like “ small steam engines,” and the transmitters “ might be taken for hot-water boilers engineers explaining that this is because of the principle of “ resonant lines,” which also eliminates crystal control. There is also the “ shoe-button ” or “ acorn” valve specially designed for micro-wave service.