• Plug and play module https://www.sv1afn.com/dra818.html
• Datasheet: dra818v-datasheet.pdf
• VHF Schematic: dra818-vhf-schematic.pdf

DRA818 VHF Voice Transceiver Module

DRA818 VHF Module connected to Raspberry Pi

• Modify if needed:

  #!/usr/bin/python3
  
  import serial
  
  serport = '/dev/ttyAMA0'
  baud = '9600'
  
  channelspace = '0'      # 0=12.5kHz, 1=25kHz
  
  rxfreq = '144.8000'     # TX frequency
  txfreq = rxfreq         # Same as rx freq.
  
  squelch = '1'           # 0-8 (0 = open)
  
  txcxcss = '0000'        # CTCSS / CDCSS
  rxcxcss = txcxcss       # CTCSS / CDCSS
  
  
  ser = serial.Serial(serport, baud, timeout=2)
  print('Opening port: ' + ser.name) 
  
  print ('\r\nConnecting...')
  ser.write(b'AT+DMOCONNECT\r\n')
  
  output = ser.readline()
  print ('reply: ' + output.decode("utf-8"))
  
  print ('\r\nConfiguring radio...')
  config = 'AT+DMOSETGROUP={},{},{},{},{},{}\r\n'.format(channelspace, txfreq, rxfreq, txcxcss, squelch, rxcxcss)
  ser.write(config.encode())
  output = ser.readline()
  print ('reply: ' + output.decode("utf-8"))
  
  print ('\r\nDisabling filters...')
  ser.write(b'AT+SETFILTER=0,0,0\r\n')
  output = ser.readline()
  print ('reply: ' + output.decode("utf-8"))
  
  print ('\r\nSetting volume...')
  ser.write(b'AT+DMOSETVOLUME=1\r\n')
  output = ser.readline()
  print ('reply: ' + output.decode("utf-8"))

Dire Wolf is a software “soundcard” modem/TNC and APRS encoder/decoder. Source code: https://github.com/wb2osz/direwolf

• Create ~/.asoundrc:

  pcm.!default {
          type plug
          slave {
                  pcm "hw:1,0"
          }
  }
  
  ctl.!default {
          type hw
          card 1
  }

• Mixer settings:

  # Set Microphone levels, mute loopback
  amixer -c1 sset Mic playback 0% cap mute
  amixer -c1 sset Mic capture 75% cap mute
  
  # Set Headphone level
  amixer -c1 sset Headphone playback 70% cap unmute
  
  # Disable auto gain control
  amixer -c1 sset 'Auto Gain Control' cap mute

• direwolf.conf:

  MYCALL <callsign>
  MODEM 1200 E+ /3
  TXDELAY 20
  PTT GPIO -4         #RPI GPIO 4

Configure the radio with pre/de-emphasis and filters, see script above.

• Text-to-speech example:

  # Set pin 4 as output
  raspi-gpio set 4 op
  
  # Transmit
  raspi-gpio set 4 dl
  
  echo "<callsign>" | cwwav -f 700 -w 20 -o morse.wav && aplay morse.wav
  
  /home/pi/.local/bin/google_speech -l nl "Dit is <callsign>, met een testuitzending."
  
  # Receive
  raspi-gpio set 4 dh