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 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.
Looking inside Rahul 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.
Make the VU version.. The isolation transformer was the most critical part of the equipment. Initially he used one salvaged from modem cards but this was not acceptable if many units were to be made and 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 1500 turns primary and 1500 turns secondary with 44 SWG wire. Assemble it back. Purist may also add a layer between the two windings and ground one end to make a Faraday shield.
The next item was the opto coupler 4N33 with Darlington pair transistors in its output. (The 4N35 is more commonly available, it can be used with an additional 2N2222 to boost the output current and gain.) He used commercially available 6 x RCA sockets used in VCD players. The 8 pin Mic connector was replaced with a more readily available PC keyboard connector 5 pin DIN. The 9 pin D shell is common so he retained it. Instead of PCB jumpers, he left it to the home brewer to hardwire the connections with shielded wire. i.e.
1. Mic and Ground.
2. PTT and Ground.
With shield going to respective grounds. As he felt this method is simpler and every home brewer will at least have this much information about his rig. Do not be tempted in using keyboard lead with 5 pin DIN connector molded , these are prone to Hum pickup. Use two lengths of single core shielded wire for respective connections.
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