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Engineers Describe Television’s Microwave Relay System as Simple

November 17, 1953

Spokane Daily Chronicle

Television engineers and technicians will tell you that there’s nothing complex about the microwave-radio relay system that soon will be beaming live network TV programs into Spokane.

But the layman trying to grasp some of the fundamentals of that system’s operation is likely to find it anything but simple and uncomplicated.

To build the 247-mile-long network linking Yakima and Spokane, the Pacific Telephone and Telegraph Company not only had to install transmission and receiving equipment at the system’s two terminals; it also had to erect six repeater stations.

Installation Costly

Total cost of the entire installation has been set right around $3,000,000, Warren Green, the company’s chief technical man in Spokane, said today. Each of the repeater stations alone required an expenditure of about $275,000.

Some misconceptions exist about these repeater stations, he said. For example, he continued, many people think a high tower is situated at each of them.

“It’s true that microwaves need a straight, unobstructed path, or ‘line of sight,’ between the one point and the next to which they’re beamed,” he said. “So repeater stations usually are placed on high ground to clear any obstacles.”

But a tower isn’t necessarily required, especially if the ground is high enough—and only one tower had to be built along the Yakima-Spokane route.

It’s a 162-foot-high structure at Sprague, the repeater station from which the television-transmitting microwaves are beamed to Browne’s Mountain, then across the final, short seven-and-one-half mile lap to antennas atop the main PT&T structure at W301 Second.

From Yakima, terminal point of a coaxial cable over which television is transmitted from Seattle, the microwaves are beamed to successive stations at Blue Light in the Horse Heaven Hills, Kennewick Hill, Clyde (50 miles north of Walla Walla), Benge—then to Sprague and Browne’s Mountain.

Each station is in itself a self-sustaining, unmanned marvel of modern technical achievement. Through a complex alarm system linking each to a control station in Pasco, any trouble developing at any of the stations immediately can be pinpointed.

“That alarm system will identify as many as 40 different types of failures, ranging from any type of mechanical breakdown to an effort by some unauthorized person to break into one of the units,” Green said.

Amplifying equipment at each of the stations sustains and “builds up” the strength of the microwaves, he said.

Antennas Receive

When the microwaves at last reach Spokane—a fraction of a second after they leave Yakima—one of the two antennas atop the PT&T building will be “lined up” to receive them and channel them through the last pieces of equipment before they are sent on to one of the city’s two TV stations.

The other antenna, Green explained, will be for transmission purposes—but it will not be ready for use until some time next year.

Built of aluminum, each antenna weighs about 2200 pounds. Each has a 10-foot-square lens constructed of plastic foam and aluminum strips. Each tapers back to join a hollow, plastic-covered copper tube.

Down this tube, Green said, the microwaves will be channeled to a transmitter receiver bay on the building’s seventh floor, where the final processing starts.

The hollow tube is filled with compressed air and TV impulses now are transmitted in this manner rather than through copper wire.

Frequencies High

“Television frequencies are so high they couldn’t be transmitted any distance on copper wire without being lost,” Green said. “That’s why the hollow pipes are used. The pipes just guide the microwave to the receiving equipment.”

Some of this equipment is located on the PT&T Building’s seventh floor, some on the eighth.

On what is called a frequency modulation receiver, the TV picture can be seen for the first time since it left Yakima, Green said. The gadget is equipped with a small seven-inch TV screen.

“The picture quality can be checked by technicians at this point,” he went on. Another device, known as an oscilloscope, shows the pattern of the microwave, and that pattern can be checked against the picture.

And if the picture shows impairments, it then can be checked against the wave pattern and the flaws detected and corrected, Green emphasized.

Impulses Ready

Finally, he said, the TV impulses will be ready for transmission to Spokane’s two television stations—by microwave to KHQ and by coaxial cable to KXLY.

Throughout this entire process, he said, picture and sound travel separately, the picture beamed by microwave and the sound carried over regular Bell system circuits. They are joined at last in the telephone building’s TV operating center.

For weeks now, Green said, a crew of about 25 men has been carefully checking over the entire Yakima-Spokane microwave-radio relay system, getting it ready to go into service.

When the system isn’t in use transmitting television, it can carry long-distance telephone conversations, he said.

The system is set up to handle six television channels. Each channel can transmit either a single TV “picture” or as many as 600 long-distance telephone conversations, Green added.

Tuesday, November 17, 1953


From → KHQ, KXLY

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