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TECH TIPS |
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A Simple Interface for PSK31 or SSTV |
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This project started when I sent away to a well known supplier for an interface. This was required for a club project. The cost, around £40. It was fitted into a little 9 pin plug for a com port on the computer. Being a tight sort of person the brain went into gear. I searched the web and found various ideas. The help files supplied in the software for Digipan were the main circuit ideas for this project. Receive To receive signals and decode them you just need to connect the line out from the rig to the line in on the sound card of your computer. That is it as simple as that. If your rig haven't a line out connecter, then use the audio out jack. The advantage of line out supply is that the output is not altered by the volume control and the level matches the input level of the sound card, (1 volt p p). Transmit The circuit is split into two parts. The transmit audio and the actual transmit line (PTT). The transmit audio enters the circuit board and is attenuated to about 10mv to supply the microphone input. Some rigs have an audio input at the rear of the rig, my Yaesu FT-840 does not. The PTT line is controlled by the output of the computer com port. Depending on the software used, the pins used to control the PTT line differs. This interface detects the pins in use. |
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You will notice from the circuit diagram below that the output from the com port is selected by the diodes, D1 & D2. The transistor is turned on by the appropriate line. This in turn grounds the trasmit line on the rig. |
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This interface can also be used with Hand Held units for Packet, SSTV and PSK 31 on the 2m band. Give it a go. There are a lot of good web sites out there on the subject of interfacing your rig. If you do have trouble, feel free to e-mail me at the club. barc@radio-club.fsnet.co.uk Good luck and happy Digital. |
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My FT-840 wired ready to go (I will have to tidy up the cables) |
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Diodes 1N4148 Resistor 10K 1/8 w Transistor BC337 |
