indicators   in   the   following   text.   Each   number corresponds to a pointer in figure 1-8. 1.  Preset  channel  selector  switch–Selects  anyone of  20  preset  channels. 2. CHAN indicator–Indicates channel selected by the preset channel selector. 3. SET switch–Sets anyone of the available 7000 normal  mode  frequencies. 4.  MEMORY  read  display–Displays  the  fre- quency that has been selected by preset channel selector. 5.  Memory  READ  switch–Allows  selected  fre- quency to be displayed. 6.   Manual   frequency   selector   switch–Selects hundredth and thousandth’s digit of the desired manual frequency in steps of 25 (00, 25, 50, or 75). 7.  Manual  frequency  selector  switch–Selects  the tenth’s  digit  of  desired  manual  frequency  (0  through  9). 8.   Manual   frequency   selector   switch–Selects unit’s digit of the desired manual frequency (0 through 9). 9.   Manual   frequency   selector   switch–Selects ten’s digit of the desired manual frequency (0 through 9). 10.  Manual  frequency  selector  switch–Selects hundred’s  digit  of  the  desired  manual  frequency  (either 2 or 3). In the A position, the radio set in an anti- jamming mode. In the T position, the radio set is enabled for  transmission  and  reception  for  one  minute. 11.  Function  selector  switch–Selects  operating modes. a.  OFF–Shuts  down  the  radio  set. b.  T/R–Enables  main  receiver  and  transmitter. c.  T/R+G–Enables  main  receiver,  transmitter, and guard receiver. d. ADF–Sets the receiver transmitter to the AM mode   for   automatic   direction   finding operations. e. SATCOM–Allows Satellite Communications by setting the receiver transmitter to the SATCOM  mode. 12.  FAULT  status  indicator–Steady  illumination indicates an RT fault, a slow flash (1/sec) indicates an interface fault, and a fast flash (4/sec) indicates a control box  fault. 13.  TONE  switch–Enables  transmission  of  an audible  tone  on  the  selected  frequency. 14.   SONOBUOY   COMMAND/MANUAL/ PRESET/GUARD–This  switch  selects  the  mode  of frequency  selection. a. b. c. d. SONOBUOY  COMMAND–This  position causes the radio set control to deliver a serial data  stream  corresponding  to  a  preset frequency in the controls memory. MANUAL–In this position the frequency is manually selected using the five manual frequency  selector  switches. PRESET–The frequency is selected using the  preset  channel  selector  switch.  This position is also used for programming the 20 preset channels. GUARD–This  automatically  tunes  the  main receiver   and   transmitter   to   the   guard frequency and disables the guard receiver. 15.   SQUELCH   ON-OFF   switch–Enables   and disables the squelch circuits of the main receiver. UHF-2 Antenna Select Panel The  UHF-2  antenna  select  panel  (fig.  1-9)  selects which antenna the UHF-2 radio set will use during operation.  There  is  one  two-position  switchlight  on  this panel. The switchlight is marked UP ANT and LOW ANT. When the upper tailcap antenna is selected, the UP ANT  portion  of  the  switchlight  will  be  illuminated amber. When the lower antenna is selected, the LOW ANT portion will be amber. UHF MODES OF OPERATION Figure 1-10 shows a simplified block diagram of the UHF  system. The UHF-1 radio set provides the following modes of operation: plain voice, cipher voice, ADF navigation, plain  voice  guard,  cipher  voice  guard,  and  secure SATCOM.  The  UHF-2  radio  set  provides  plain  voice, cipher voice, sonobuoy command, wide-band audio, plain voice guard, cipher voice guard, link 11 plain data, link 11 cipher data, TTY plain data, TTY cipher data, and IACS data. Operation of these radio sets is supported by various equipment on board the aircraft. Mode selection for UHF-1 is accomplished by the control box and the A344 voice   selector.   Mode   selection   for   UHF-2   is 1-14