Technical Digests: Ship Sets for Harbor Ship-to-Shore Service

must permit operation by non-technical personnel and require a minimum of power for their proper functioning. The striking similarity between these conditions and those already encountered in the furnishing of radio telephone equipment to aircraft permitted the use with small modification of a radio system already proved by years of use on this country's major airlines. The ship transmitter, coded the 13-A, has an output of 50 watts. Its size is 13f" X 181" X 10", its weight about 34 pounds. The tube complement comprises a 5-watt audio-frequency amplifier tube, a 5-watt oscillator tube which is controlled by a quartz crystal oscillating at one-half the desired frequency and connected to the grid circuit of the oscillator tube, and a 50-watt screen grid tube as a first radio-frequency amplifier. The coupling from the oscillator is supplied by a radio-frequency transformer which freely passes the first harmonic of the quartz plate to drive the first radio-frequency amplifier. The output stage consists of two similar tubes in parallel to form a second radio-frequency amplifier. The two radio-frequency amplifier stages are coupled by a transformer which also acts as a band-pass filter and freely passes the output frequency. The two radio-frequency transformers are mounted in a single plug-in unit. The audio amplifier modulates the screen bias on the first and second radio-frequency amplifiers, giving substantially one hundred per cent modulation. The filament of each of the three radio-frequency amplifier tubes is in series with a ballast tube to protect them from fluctuations in the power supply.