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HamComm Interface for ham or shortwave.

This is the small easy to build interface that will allow you to receive most all the digital modes on you shortwave radio. Remember, the set must have a BFO, or USB, LSB setting as the data is sent in tones as you would hear on a modem speaker. The BFO, or SSB setting will convert signals to tone and then go to the interface, and then to the serial port of the computer to be analyzed. This interface is the most widely used and 100's of programs used this interface. If you do not want to use this interface, you will have too look for software that will allow a direct hookup from your headphone jack of the reciever directly into the line in, or mic input of your soundcard.

HamComm Interface schematic

This design is made up from three parts: The receive section, the transmit section and the PTT section.
The heart of the unit (receive section) is based around a common op-amp I.C which acts as a comparator. Audio taken from your receiver is fed to the input and the output is squared before entering the computer port.

Output from the RS-232 port, pin-3 (TXD) is fed through the resistor/capacitor network before entering your transceiver. Some constructors may wish to omit the two back-to-back diodes. These tend to 'square' the wave form of audio and omitting these will give a more 'rounded' wave similar to a sine waveform.
The 10K variable resister attenuates the signal.

The PTT circuit is taken from pin-7 (RTS) and fed to the NPN transistor. When the base pin is taken "high" the collector goes "low" thus switching the PTT circuit in your rig.

No external supply is needed as the circuit is self-powered from the computer.

HamComm Interface schematic

HamComm Interface schematic


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