The total range to target is controlled by the number of one mile incre- 

 ments set by switch positions on the range unit. This operation is initiated at 

 the Precision Ranging Unit, which introduces a delayed sweep trigger on the radar 

 display. For example, if the delay switch were set at 1 mile, the portion of the 

 sweep around the target would be linearly expanded so that a one -mile range 

 would cover the full radius of the radar display. This magnification reduces 

 the error associated with visual alignment of the target and the variable range 

 marker. 



b. Remote Electrical Track Plotter 



The Model 429 Precision Remote Electrical Plotter utilizes a pair of 

 synchro-controlled ball bearing mount screw boxes which change the length and 

 thus the position of the apex unit at the head of a set of precision lead screw rods . 

 The apex unit is caused to follow and mark the hydrographic or navigational track 

 by the operator as he follows target range changes at the ranging unit. The lead 

 screw boxes are set over and pivoted around points on the area chart which are 

 chosen as the operating targets . A solenoid -operated pointer automatically 

 marks the chart at a preset rate or may be manually operated. 



c . Radar Transponding Beacon 



The Model 427 Radar Transponding Beacon is designed primarily for 

 use as a precision radar target and operates in conjunction with a precision 

 radar surveying system . Because of its small size and low power consumption, 

 it is useful as a remote radar navigational beacon and aid, surface buoy trans- 

 ponder, etc. The transponder is capable of operating with any single pulsed 

 radar operating in the frequency band of 9300-9400 mc with a pulse repetition 

 rate of up to 2000 pulses per second. 



In the quiescent mode of operation, the transponder operates in a 

 listening condition only. That is, the receiver is on and available to amplify 

 signals . In this mode the receiver draws 1/4 watt from the 12 -volt dc supply. 



Upon receipt of an X-band signal from an interrogating radar, a relay 

 circuit turns on the magnetron filaments . After a suitable warm-up time, 

 coded pulses are transmitted at a preset rate. After radar interrogation ceases ^ 

 a time delay holds the transponder in an active condition for approximately 2 

 minutes and then allows the transponder to return to the quiescent condition. 



A horizontally polarized omnidirectional antenna is used for both the 

 transmit and receive functions . A ferrite three -part circulator isolates the 

 transmitting and the receiving circuits . 



139 



attbtir 31.1tittlf,I(nr. 



