AEROGRAPHER'S MATE 3 & 2 



INDICATORS. — Three indicators are mounted 

 on the front panel of the R-390A. The fre- 

 quency indicator dial indicates the frequency 

 to which the receiver is tuned. This dial is of 

 the digital- counter type, which perm its frequency 

 to be read directly with little chance of mis- 

 reading. 



The CARRIER LEVEL indicator — a meter — 

 measures the level of the RF signal appearing 

 at the input of the receiver. The operator will 

 find this meter valuable in tuning to the exact 

 frequency that gives the strongest signal. It 

 is also used to indicate proper adjustment of 

 the antenna trimmer. The indicator labeled LINE 

 LEVEL monitors the level of the line audio 

 output used to drive the terminal equipment. 

 This meter is placed across the output circuit 

 by the LINE METER switch. The three avail- 

 able values of meter sensitivity (voltage re- 

 quired for full-scale deflection) are determined 

 by the setting of the LINE METER switch. This 

 meter is valuable in maintaining the proper 

 output level when making tape recordings. 



COMPARATOR-CONVERTER GROUPS 

 AN/URA-8( ) AND AN/URA-17( ) 



Converters are an integral part of every 

 radioteletype system. In some instances, the 

 keyer is built into the radio transmitter, but 

 the converter is a separate piece of equip- 

 ment. 



The AN/URA-8( ) and AN/URA-17( ) fre- 

 quency carrier shift converter-comparator 

 groups (fig. 7-14 and 7-15) are used for diversity 

 reception of Frequency Shifted Radio Teletype 

 signals. They are most commonly used on ship- 

 to-shore or ship-to-ship circuits. 



For either space diversity or frequency di- 

 versity reception, two standard Navy receiv- 

 ers are employed in conjunction with the 

 converter-comparator group. In space diversity 

 operation, the two receivers are tuned to the 

 same carrier frequency, but their receiving 

 antennas are spaced some distance apart. Be- 

 cause of the required spacing between anten- 

 nas, space diversity is usually limited to shore 





FREQUENCY 



SHIFT 

 CONVERTER 



COMPARATOR 



FREQUENCY 



SHIFT 

 CONVERTER 



RACK 



1.235 



Figure 7-14. — Converter-Comparator Group AN/URA-8 ( ). 



136 



