Build your own PC interface

Posted on Feb 5, 2014

TNC and Modems ruled the world of digital communications until recently. With the advent of high speed computing and digital signal processing (DSP) all this has changed. If you own a home computer (PC) with a sound card, all you need to do is download software and obtain an interface between the PC and your radio. The interface provides the audio

Build your own PC interface
Click here to download the full size of the above Circuit.

and digital signal level translation between the computer and the radio. Due to lack of locally available interfaces many hams imported them for large sums of money. It occurred to me that I could build an interface easily. Typically being lazy, I needed a push to get started. A swift kick in the rear would be a more appropriate term. This was provided by Miku, VU2WAP. He offered me his Rigblaster Nomic for reverse engineering. Looking inside I found a 600 ohm 1:1 audio isolation transformer for PC to transceiver mic input and presets for level control An optocoupler was used for PTT keying. On the outside there was an 8 pin mic connector or RJ45 optionally. Stereo earphone (EP) sockets for soundcard connections. A DB9 connector for RS232 PC COM port connection. To adapt to various brands they provided internal jumpers. The isolation transformer was the most critical part of the equipment. It was the hot topic of discussion with my friends on 14. 130Mhz including Zal VU2DK, VU2DAD Dev VU2NTT Neeraj, VU2WAP Miku. This transformer is not commercially available in the electronics market. Initially I used one salvaged from modem cards but this was not acceptable if many units were to be made. I designed one taking many parameters into consideration and had it fabricated locally. If you want to make your own it is simple, buy a driver transformer used in 6V L type transistor radio plate. Dissemble and strip its windings. Wind...

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