Audio Modem

Basic Settings

• Connection Name: Display name of the connection
• Auto-start: Automatically start this connection when QTH starts up
• Audio Output: Select the audio output device that is connected to your radio’s audio input or mic
• Audio Output Volume: Adjust the output volume of the selected device
• Audio Input: Select the audio input device that is connected to your radio’s audio output or speaker
• 6dB Emphasis Filter: For many transcievers, speaker audio is “de-emphasized” to attenuate the higher frequencies. Enabling this option adds a filter to the incoming audio that compensates for this.
  • If you are connecting to the radio’s speaker out, it is recommended to keep this selected.
  • If you are connecting to the radio’s discriminator audio output, deselect this option
• Audio Input Volume: Adjust the input volume of the selected device.

PTT Settings

Choose the mechanism used to trigger the Push-to-Talk (PTT) on the radio connected to the audio interface.

• None: No PTT will be used. Generally, you would use this if your audio interface is using VOX to trigger the PTT or has dedicated audio detection circuitry, like a SignaLink.
• Hamlib: Use Hamlib to control the PTT on the radio over a serial control connection.
• Serial: QTH will send a signal to the specified serial port pin, either the Ready to Send (RTS) or Data Terminal Ready (DTR). Some audio interfaces can use this signal to trigger the PTT on the radio.
• Audio Channel: When this mode is selected, a sine wave of the specified hertz will be generated on the right channel of the audio output, with the data signal on the left channel. Some audio interfaces have circuitry to detect the signal and trigger the PTT on the radio.

Advanced Settings

• Callsign: Override the callsign for this connection. If not specified, the global Callsign selected in Preferences - Station will be used. Please note: If this callsign does not match your licensed callsign, your callsign will be automatically appended to the comment field. This is to both support tactical callsigns and ensure proper on-air identification
• SSID: Enter the SSID of this connection. If not specified, the global SSID in Preferences - Station will be used
• Path Preset: Select a path preset or enter your own.
• TX Delay: Time between keying the radio and sending data, in milliseconds. The default start-up value is 50 (i.e., 500 ms).
• Persistence: The persistence parameter, p, scaled to the range 0 - 255 with the following formula: P = p * 256 - 1. See KISS Protocol for a longer explanation.
• Slot Time: Slot interval in 10 ms units.
• TX Tail: Time to hold up the TX after the FCS has been sent, in 10 ms units. This command is obsolete, and is included here only for compatibility with some existing implementations.
• Fill Duplex: Can this connection transmit and receive simultaneously.