Radio age research, manufacturing, communications, broadcasting, television (1941)

The system is also capable of sending coJe signals such as those used in teletype Furthermore, the system can, when desired, carr)' a number of conversations at the same time and unscr.imble them at the receiving point. The new microwave facilities provide the Turnpike Adininistration at New Brunswick with a means of in- stantaneous communication with all state troopers, m.iin- tenance trucks, and toll gates along the road. The dial phones and teletype link the police divisions along the turnpike with one another and with the State Police Headquarters at Trenton. Each pohce car is furnished with dual-frequency two- way radio equipment operating in the 152 to 174 mega- cycle band. The cars transmit on one of their two frequencies and receive on the other. The ver)' high fre- quency b.ise stations at the microwave towers operate on the same frequencies as the cars, reversed as to send- ing and receiving. That is, they receive on the frequency on which the cars send, and transmit on the other fre- quency. Hence, the normal path for a message trans- mitted from a car is to the nearest base station, from which it is retransmitted to other cars in the vicinity and to toll gates. At the same time, the VHF receiver at the base station feeds the message into the microwave sys- tem, where it is relayed to all other base stations and retransmitted by them. System Has Extra Features Several unusual "extra-feature" provisions make the system one of the most flexible and foolproof ever installed. In most cases, two base stations will be able to re- ceive a direct transmission from a single car. A special "sensing" and lock-out device has been provided, there- fore, to select the base station receiving the strongest signal as the one to feed the microwave system at the same time locking out the other station. The rejected station, as well as the other remaining base stations, re- ceive the message through the microwave system. If an officer in one police car wishes to talk directly to one in a nearby police car without entering the micro- wave system, he may do so by throwing a .switch which changes his transmitter to the receiver frequencies. This feature prevents local communications from tying up the entire turnpike communication system. Base station antennas are two-element arrays de- signed to concentrate a high proportion of the radiated signal along the turnpike. This insures a strong signal on the highway with a minimum {xjssibility of interfer- ence to and from adjacent communities. The radiations from two consecutive base stations RADIO AGE U necessarily overlap, and there is an area where signals from both stations are of approximately equal strength and reception would normally be distorted. To prevent this, dual antennas are mounted on the roofs of the police cars. A switch selects directional reception char- acteristic favoring the chosen base station. At the New Brunswick Turnpike headquarters, a switching arrangement permits separation of the system into two, three, or four sections. This arrangement in- creases both the flexibility and the message capacity of the system. When tied end-to-end, the system is essen- tially one large parry line. If serious vehicle traflic de- velops in any one region, the New Brunswick head- quarters can isolate that section of the communication system, leaving it free to handle its local affairs without tying up calls for the rest of the turnpike. However, headquarters is still in a position to monitor messages exchanged in the area, and can, by a throw of the switch, bring it back into the overall system. More than $100,000 has been spent on the new com- munications facilities. Towers up to 150 feet in height have been erected in or near Swedesboro, Moorestown, Bordentown, Trenton, New Brunswick, and Newark, with two near the latter city. The base stations employ 60-watt RCA radio transmitter-receiver units. In addi- tion, 15-watt fixed station transmitters are located at interchanges, maintenance buildings, and other points. More than 50 police and maintenance vehicles have been equipped with 15-watt RCA Carfone mobile units. The microwave relay equipment is RCA's latest Type CW-5B 960-megacycle equipment. Microwave relay station near Bordentown, N. J.