Building the Digital interface

 


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Click on the links below for detailed information:

Digital Interface
Computer Serial Port Cable
Computer Audio Cables
Radio to interface cable and testing
Install the board in it's case
Optional reed relay version

Introduction

This is a simple interface that will provide great digital mode communications.  The interface features a few interesting features. This is a project of the Chester County Radio club Aug 2009 meeting.

  • The computer serial port voltage can vary all over as laptops can have very low RS-232 voltages. To get around this potential problem we are using a lower résistance LED dropping resistor.

  • All connections between the computer and radio are completely electrically isolated. This is accomplished with the use of isolation transformers and an opto-isolator.  This should cut down on potential ground loops and hum.  Not to mention the possibility of differences in voltages taking out the radio or computer.

  • The audio to the radio is DC isolated with a capacitor because some radios have a phantom voltage needed for the microphone.

  • Also the radio 'audio in' is adjustable with the on-board potentiometer. This will help when the computer doesn't have an audio out jack and you will have to use the speaker jack and its level can be way too high for the radio.  A center setting of the pot will be a good ball park setting.


The Club Website will have the latest version of these directions. 
Take a look at http://w4fhu.org/digital  or contact me at joel@cyberbest.com