This method is instead of buying a RigBlaster type device.
- PSK31 or other digital modes: 1.0µF series capacitance for TX audio.
- voice modes such as Echolink: 0.001µF series capacitance for TX audio.
The 0.001 µF series capacitor provides a high-pass filter to pre-emphasize the audio into the flat TNC 10Kohm audio input. Otherwise, the audio will sound like a broadcast radio with the Tone control turned fully counterclockwise (overly bassy audio).
The 1.0µF shunt capacitor provides a low-pass filter to de-emphasize the audio into the flat computer input for RX voice audio. Otherwise the audio may sound tinny (like Tone control turned fully clockwise).
PC-Radio interface: Squelch Control
You could use VOX to control the squelch open/closing, but it is much preferable to have a hardwired connection for smooth operation when linking repeaters etc. This interface can be readily built with simple parts and shielded audio cable (or use cords from old mice/keyboards).
It assumes that your radio has a TNC port, with 3..15V “shorted to ground” to transmit. Connect transmit audio from the PC Line out into the radio’s TNC port “Data In” pin, and the computer Line In to the radio’s TNC port “1200 baud Data Out” port.
Radio w/o TNC port
It is also possible to use the microphone jack and speaker audio if no TNC port exists. Using the microphone jack for Line Out audio requires you to check to be sure there is no DC voltage on the mic pin! You might damage your radio otherwise. Use a 1.0 µF capacitor to block the DC.
Using the speaker jack for Line In audio is undesirable, since volume control changes upset audio levels, but sometimes that’s the only recourse. In some cases, you may have too high an audio level. Consider then constructing a voltage divider, with a 10000 ohm series and 1000 ohm shunt resistor.