Hi, Described here is a circuit setup for interfacing PC soundcard with radio equipment for transferring digital as well as analog base band signal in audio frequency range. Requires modem software for modulation and demodulation of baseband signal.
Figure 1 Schematic Diagram
It uses three isolation transformers, of which one dedicated to PTT engages PTT logic of rig by using the right channel 1 KHz signal generated by software during each data transmission as a routine once configured.
Isolation Transformer Core Details
Isolation transformer uses MnZn ferrite toroid used in switching power supply and RF suppression ferrite bed’s, also found applicable for frequencies up to 1MHz including audio range. One can recycle toroid from old CFL’s as well as Electronic florescent lamp chokes. Toroid tested and used in this circuit is from ferrite manufacturer “Mahindra Hinoday” form VU land with mix type MSB-5S and part number –T10.
Figure 2 Frequency vs. Permeability of toroid MSB-5S
Transformer winding Details
Primary and secondary are maintaining 1:1 ratio in all three transformers. Each transformer consists of 150 bifilar turns of (39-42) SWG wire serving primary and secondary. One can also try separate individual windings instead of bifilar.
Figure 3 Toroid winding and Dimension
Software configuration involves configuring windows audio setup as well as modem software. Here fldigi is the software modem used. Following settings gave me optimum result.
Windows Audio Settings
Figure 4 Setting the Right and Left Channel speaker gain
Figure 5 Microphone gain setting
Modem Software Settings
Figure 6 Check the parameter PTT tone on Right channel
|Figure 7 Also check the PTT on right audio channel under Hardware PTT|
PCB & Circuit: Download Link
|PC-Rig interface (my prototype on dot board)|