Chapter 7 — COMMUNICATIONS EQUIPMENT AND OPERATIONAL PROCEDURES 



34.15 

 Figure 7-11. — Radio Receiver R-390A/URR. 



R-1051/URR 



The R-1051/URR (fig. 7-12) is one of the 

 newest radio receivers. It is a versatile super- 

 heterodyne receiver capable of receiving any 

 type of radio signal in the frequency range of 

 2 to 30 MHz. It can be used as an independent 

 receiver, or, in conjunction with a transmitter, 

 to form a transmitter-receiver combination. 



Basically a crystal-controlled equipment, the 

 R-1051/URR employs a digital tuning scheme 

 for automatic tuning to any one of 56,000 op- 

 erating channels. A display window directly 

 above each control provides a readout of the 

 digits to which the controls are set. The 

 R-1051/URR has 0.5 kHz tuning whereas the 

 R-1051B/URR tunes in 0.1 kHz increments or 

 2 to 30 MHz with continuous vernier tuning 

 between 1 kHz increments. 



This receiver is designated as standard equip- 

 ment for use aboard all ships. 



Receiver Tuning 



The operating characteristics of the R-390A/ 

 URR Radio Receiver were discussed earlier. 

 The R-390A/URR being a representative receiver 

 will be covered here for receiver tuning. 



Haphazard operation or improper setting of 

 receiver controls can result in poor reception. 



It is important, therefore, to know the function 

 of every control. Although much of the Navy's 

 communication equipment is set up or tuned 

 automatically, an operator must still do a lot 

 to obtain proper performance from the equip- 

 ment. (Most mechanical or electrical equipment 

 is only good as the person operating it.) Refer 

 to figure 7-13 when studying the following de- 

 scriptions of switches and controls. 



FUNCTION SWITCH. — The function switch 

 serves several purposes. It has a number of 

 positions, each of which is discussed. Its OFF 

 position (self-explanatory) simply turns off power 

 to the receiver. 



When the function switch is in the STANDBY 

 position, the tubes are heated to operating tem- 

 peratures but are not operating. This condition 

 readies the receiver for instant use without a 

 long warmup time. 



The abbreviation AGC stands for automatic 

 gain control. Placing the function switch in the 

 AGC position activates the circuitry, which auto- 

 matically adjusts the RF and IF amplifier gain 

 to compensate for variations in the strength 

 of the incoming signal. In connection with the 

 AGC function, notice that the AGC switch at 

 the top of the panel has three positions marked 

 SLOW, MEDIUM, and FAST. This AGC switch 

 adjusts the rate at which the AGC circuitry 

 responds to a change in the signal strength. 

 The correct position of the AGC switch depends 

 on the type of signal received. 



The abbreviation MGC stands for manual 

 gain control. When the function switch is in 

 the MGC position, the AGC circuitry is not 

 activated, and the gain is controlled manually 

 by means of the RF GAIN control. 



When the function switch is in the calibrate 

 (CAL) position, a stable crystal oscillator in- 

 troduces a signal at the imput circuitry of the 

 receiver. This signal allows the operator to 

 calibrate his receiver; that is, to ascertain that 

 the reading of the tuning dial corresponds to 

 the frequency received. The calibration circuitry 

 of the R-390A permits the operator to calibrate 

 the receiver at each 100-kHz point throughout 

 the tuning range of the receiver. In connection 

 with calibration, notice the ZERO ADJ knob 

 near the frequency dial. When turned clockwise, 

 this knob disengages the frequency indicator 

 from the KILOCYCLE CHANGE tuning control. 



133 



