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Sound Card PSK31 and other Digital Modes InterfacingHardware Setup (basic interfacing) Use shielded leads. Connect the audio output from the radio to the line or mic input of the sound card. Connect the output of the sound card to the microphone, aux microphone, or data input of the radio. Attenuation The second step is the one that causes problems. You should insert an attenuator in the sound card output line to reduce the audio level or you may overdrive the audio stage of your transmitter. Some transmitters already have an attenuator or voltage divider, but even these often operate well with even more signal reduction in the line between the sound card output and the radio mic or audio input. Here is a picture of a 100:1 voltage divider to use as an attenuator. You can replace one or both resistors with potentiometers for more adjustment, but usually a 100:1 works fine.
Depending on your individual setup, you may want to add ferrite beads to the input and output leads, and possibly decoupling capacitors. Of course, these might be needed even without the attenuator. More Detailed Info on Interfacing by WM2U Keying InterfacesSome of his example connections for keying the transmitter are below. I recommend using the following type of interface to key your transmitter using the RTS line using a COM port. All of the software available allows you to control TX and RX via a spare port. This interface will reduce the probability of a ground loop problem. You cand use one or both of these schematics They use an Opto Isolator to switch the circuit. The Opto Isolator is a 4N25, 4N29, ECG 3084, PS2601 or equivalent from Digi-Key, Newark or Radio Shack, I used a TIL111.
There are lots of already built interfaces available from MFJ, Mountain Radio, BuxComm, and other companies. |
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Dick Cullen, PO Box 15053, Colo. Springs, CO 80935 All material Copyrighted by Blarney Manx and R&R Enterprises
Last Updated - 07/04/04
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