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 Introduction to Sound Card Interface & Radio Modems:


SC1: Simple Sound Card Interface (Discontinued)

SC1: New Project

SC2: Advanced, Sound Card & Echo Link Interface

 SC1: Discontinued


New SC1 Sound Card Interface Project is here


For many radio amateurs, talking & chit-chatting on-the-air is of no interest. They rather like to "Silently" work on their bench with hobby projects & communicate with fellow amateur by way of a PC and a modem connected to wireless set.

There are lots of ideas & radio modems available to fill this requirements. I have gone thru this 15 years back when I first bought a Kentronics all mode TNC and later a 1200baud VHF TNC. 

Here I have presented two such "Modems" which are not really modems but give us the same results at a fraction of cost.

The first is called "Hamcom" a PC software (DOS) written by  . It has a very simple interface to PC com port containing a ua741 and few components. Most work of a "TNC" is done by the software.

You get a simple, economical & fast way to start digital communication on amateur bands with this kit & a free software. With Hamcom you can receive & transmit RTTY & CW.

Similarly, PC's soundcard is nothing more than a modem itself. Using soundcard capabilities for Digital Communication has attracted many hams to use a simple interface to isolate PC & Radio to achieve clean signals & reject noise and spurious frequencies.

Sound card Interface detailed below does this.

 Sound Card Interface for Amateur Radio Stations:
As discussed above, PC's sound card is nothing but a modem, a term defined as "modulator" and "Demodulator". In short, it converts digital zeros & ones to sound tones and again, sound tones to digital levels.

The soundcard interface detailed here is not different from many made by amateurs and available commercially.

However, I have made it simple to construct and easy to use. On this interface, you have a 5pin DIN connector where you can connect your microphone and use a shielded cable to connect Mic, Mic ground & PTT to your radio's Mic Connector.

A push switch is provided to change over from digital mode to microphone. And another push switch is provided to monitor Rig (Radio) Speaker output. (requires a speaker connected on this switch, not included in kit)

You have choice to use this interface with or without DC Power. It will work equally well in both situations. Great for your Portable Rigs. 

Since most people do not require a PTT relay, Reed Relay may be ordered as an option. 

Two reed relay options are available: 5V and 12V.

5V reed relay is required where supply voltages are below 12V. 12V Reed Relay is standard with most desktop supply source of 12-13.8VDC. 

If 5V reed relay is used, a series resistor would be required, which may be placed instead of Diode D6 (1N4001).

Picture of the Assembled SC1 Sound Card Interface:
                   Top View  of the Assembled Sound Card Interface

Click the photo to enlarge


 Technical Details & Schematic:
Sound Card Interface Document
Schematic & Parts List



Make your own PCBs. Gerber files for PTH PCB

Component Data Sheets

 Project Component Datasheets

With sound Card Interface, you can use many software available either as a freeware or shareware. Please go thru following links & find one suitable to your communication requirements.
Collection of Digital Communication Software
More Digital Communication Software links
Look under "Digital Communication" and Packet, Amtor, CW, Pactor etc.


 Free Software Utilities Download
Wave Generator
PCBs for this project may be available from our shop at foxdelta.net: 

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