DESIGN OF SYSTEM — NORTH ATLANTIC LINK 



47 



TRANSMITTING 

 AMPLIFIER 



TEMP 

 EQ 



TRANS 

 EQ 



LOW 

 PASS 

 FILTER 



DEVIATION 

 EQUALIZER 



TO INPUT 

 OF CABLE 



Fig. 4 — Transmitting equalizers — block schematic. 



A portion of the transmitting terminal is shown in block schematic 

 form in Fig. 4. All of the equalizers are constant resistance, 135 ohm un- 

 balanced bridged-T structures. Their functions are as follows: 



Transmitting Temperature Equalizer — It was estimated that the cable 

 loss change from temperature variations would not exceed ±5 db at the 

 top of the transmitted band. The change in cable loss versus frequency 

 due to temperature variations is approximately the same as if the cable 

 were made slightly longer or shorter, and so the temperature equalizer 

 was designed to match cable shape. Temperature equalizers are used 

 both in the transmitting and receiving terminals to minimize the signal- 

 to-noise degradation caused by temperature misalignment. Each equal- 

 izer provides a range of about ±5 db at the top of the band, the loss 

 being adjustable in steps of 0.5 db by means of keys. See Fig. 5. 



This range might appear to be more than necessary, but it must be 

 borne in mind that the sea bottom temperature data left much to be 

 desired in precise knowledge of both average and range. 



Transmittiiig Equalizer — The transmitting equalizer was so designed 

 that with the temperature equalizer set at mid-range and with repeaters 

 that match the cable loss, the signal level on the grid of the output tube 

 of the first repeater would be flat with frequency. The loss-frequency 

 characteristic is shown on Fig. 6. 



L.P. Filter — This filter transmits signals up to 164 kc and suppresses 

 by 25 db or more, signals in the frequency range from 165 to 175 kc. Its 

 purpose is to prevent an accidentally applied test tone from overloading 

 the deep sea repeaters should such a tone coincide with the resonance 



Fig. 5 — Transmitting temperature equalizer. 



