Ship Sets for Harbor Ship-to-Shore Service * 



By H. N. WILLETS 



A STUDY of conditions on board fishing trawlers and harbor craft 

 indicates that the radio units must be small in size, rugged in 

 construction and adaptable to remote control. Further, the units 

 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 18|" 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 trans- 

 formers 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. 



The quartz crystal oscillator has the recently developed low tem- 

 perature coefficient cut and the crystal holder is arranged with a heater 

 which operates only should the temperature drop below zero Centi- 

 grade. The transmitter is arranged for one, two or three carrier 

 frequencies, each requiring a separate crystal. If more than one fre- 

 quency is provided, change from one to another is accomplished by a 



* Digest of discussion prepared for Pacific Coast Convention, A. I. E.E., August, 1935. 



713 



