TM 1-1510-218-10 3A-24 (4)   GYRO SLAVE / FREE Switch.  Controls system mode of operation. (a)   SLAVE.      Places   system   in   SLAVE mode. (b)   FREE.        Places    system    in    FREE mode. (5)   INCREASE / DECREASE Switch.   Provides manual fast synchronization for the system. (a)   INCREASE.    Causes  gyro  heading output to increase. (b)   DECREASE.    Causes  gyro  heading output to decrease. 3A-22.  VOR RECEIVERS (VIR-30). a.   Description. Two     VOR     receivers     are provided.  VOR No. 2 is identical in operation to VOR No.   1   except   that   no   marker   beacon   section   is provided   in   VOR   No.   2.   The   unit   is   an   airborne navigation-communications  radio  whose  function  is  to receive and interpret VOR and localizer (LOC) signals in   the   frequency   range   of   108.00   to   117.95   MHz, glideslope signals in the frequency range of 329.15 to 335.00  MHz,  and  marker  beacon  signals  to  75  MHz.   Signal  reception  is  limited  to  line-of-sight  and  by  the power of the transmitter with a maximum range of 120 miles.      The   VOR   receivers   are   protected   by   two 2-ampere  circuit  breakers,  placarded   VOR   #  1  and VOR   #   2,   located   on   the   overhead   circuit   breaker panel. b.  Associated Controls and Functions.   Refer to Figure 2-17, Sheet 1. (1)   Pilot's  VOR  1 /  VOR  2 Switch.  Controls course select and display circuits of the pilot's HSI. (a)   VOR   1.      Circuits   are   connected   to VOR No. 1 receiver. (b)   VOR   2.      Circuits   are   connected   to VOR No. 2 receiver. (2)   Copilot's     VOR     1     /     VOR     2     Switch.   Controls   course   select   and   display   circuits   of   the copilot's HSI. (a)   VOR   1.      Circuits   are   connected   to VOR No. 1 receiver. (b)   VOR   2.      Circuits   are   connected   to VOR No. 2 receiver. NOTE If  the  pilot's  and  copilot's  VOR  1  /  VOR  2 switches are in the same position, the pilot has  control  of  the  course  select  circuits  of the  selected  receiver  and  the  copilot  can only   monitor   deviation   information   from the   selected   receiver.      A   PILOT   SELECT indicator will illuminate to notify the copilot that  he  has  selected  the  same  receiver  as the pilot. (3)   A   Indicator.      Illuminates   when   passing over airways marker station. (4)   O   Indicator.      Illuminates   when   passing over outer marker station.   (5)   M   Indicator.      Illuminates   when   passing over middle marker station. NOTE Refer to Figure 3A-1  for  items  (6),  (7),  and (8). (6)   AUDIO VOR Switch.  Applies VOR audio to respective headsets. (7)   MKR    BCN    HI-LO    Switch.        Controls sensitivity of marker beacon receiver. (8)   MKR BCN VOL Control.  Adjusts volume of received signal. c.   Controls  and  Functions.    Refer  to  Figure 3A-14. (1)   Frequency Indicator.  Indicates operating frequency of set. (2)   Frequency     Control.          Selects     desired operating frequency. (3)   NAV TEST Push Button.   When pressed, the following indications are presented: (a)   RMI Single needle indicates 5°. (b)   HSI   Lateral   deviation   to   the   right. Glideslope deviation down. (4)   VOL  /  OFF  Control.    Turns  set  on  and adjusts volume.