To determine the effect of improved equalization on the performance of TD‐2 radio relay systems, an experimental adjustable transversal equalizer has been developed. The equalizer is based on the echo principle as used in transversal filters, and operates in the 60‐ to 80‐mc frequency band. Seven pairs of adjustable leading and lagging echo terms provide flexibility for simultaneous gain and delay equalization. Directional couplers are used for tapping and controlling the echo voltages. Field experiments have shown that system equalization can be improved appreciably by the use of such equalizers.

L multiplex terminals provide the several stages of modulation required to translate telephone channels into the broad basebands which can be transmitted. on long‐haul systems. The group and supergroup equipment has been redesigned incorporating many new features. Pilot‐controlled regulators are provided to improve performance. Plug‐in modules and automated monitoring facilitate maintenance. The equipment is arranged to reduce office cabling and installation cost. By the use of transistors and other newly developed devices and components, a size reduction of 10 to 1 has been achieved and the required power greatly reduced.

Television terminals are required at circuit ends of the L3 coaxial system; at the transmitting end to condition video signals for carrier transmission and at the receiving end to detect the transmitted signals. Special signal characteristics, e.g., a degree of modulation which exceeds the value commonly referred to as 100 per cent modulation, require departures from standard modulating and detecting processes. The high degree of modulation requires both careful control of transmitted wave form and at the receiver product demodulation with phase synchronous carrier (homodyne detection). Carrier regeneration requirements result in the choice of one step frequency translation from the video frequency spectrum to the allocated vestigial sideband carrier spectrum. The one step process using a single modulator results in unusual balance requirements for the modulator itself and an unusual circuit configuration. Transmission quality objectives for the terminals are such as to permit six pairs of television terminals to operate in tandem in a transcontinental circuit. This permits a degree of interconnecting flexibility in operation with other systems, e.g., L1 coaxial or microwave systems. These objectives place severe requirements upon the transmission stability of various fillers and other circuits within the terminals. New network techniques both in design and fabrication are brought to bear in the effort to achieve required performance. The transmitting and receiving terminals are described, illustrating the functional operation and mechanical and electrical arrangements of the equipment.

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