My 1st Homebrew Digital Interface

Do you recognize this PC card ?




Yes, it is a PC Fax/Modem card from a scrapped PC.

It contains most of the electronic components needed to build a digital interface for your radio for digital mode communication. In the above picture there is the 1:1 transformer ( 600 Ohm:600 Ohm. Has the marking Atech ), below it on the right a single pole relay (CP xxxx), below that a 4C35 optocoupler, some diodes and transistors. There is also an audio circuit for a low watt speaker. Google search of stamped component numbers yields a lot of information.

By carefully removing the required components with a soldering iron and solder wick / solder sucker you can build a board that looks like the one in the photo below. 

A very simple circuit. A RS232 computer signal controlling an optocoupler so as to key the PTT circuit when in transmit mode, the audio transformer with variable resistor providing the "reduced" microphone signal.  Works well for me !!!  



All that I needed to purchase was the 9 pin female plug for the RS232 cable, the microphone connector to fit into the microphone socket of the radio and a 3.5mm speaker plug for the audio cable from the PC. 

The variable resistor, led resistor and LED were taken off other scrapped electronic boards. The board that was used to mount the electronic components was cut from a very old PC development system which used "wire-wrap" IC sockets. Total cost about R30.00

The JT65 digital software is available for free from a number of internet websites.