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Poor Ham's Signalink Project - VA3KOT John - 2020-02-25
Here is a simple maker project for a computer/radio interface for digital modes. You can buy a Signalink for a little over a hundred bucks or you can build a much simplified version that will cost around $10 which will work just fine.
Components (all available at Sayal Electronics or mail order):
1 USB soundcard
2 600 ohm 1:1 audio transformers
1 metal project box
1 USB extension cable
1 USB-A to USB-B cable (often used on older printers)
1 PS-2 extension cable
This simple circuit provides an isolated ground interface between a radio and a computer. The USB soundcard ensures that system sounds on the computer do not interfere with transmission of data. A separate USB-A to USB-B cable provides for CAT control of the radio. This cable works with my Yaesu FT-891; other radios may need a different cable. If your radio does not have a USB jack for CAT control you may need a TTL/Serial converter cable (e.g. Yaesu CT-62). If your radio does not have any kind of CAT jack you will need to provide another arrangement for PTT control (e.g. by setting VOX in your radio).
Construction takes only a couple of hours. The simplest way to connect the USB soundcard to your computer is with a USB-A male to USB-A female extension cable. The data cable between your radio's 6-pin data jack and this circuit is a PS-2 extension cable that has been cut in half. Just make sure that the required conductors (see diagram) are available. Both cables can be made at home but you will need appropriate connectors, good eyes and a steady soldering hand. If your cables are not adequately screened add a ferrite EMI suppression core at the radio and computer ends. A metal project box is recommended to avoid RF interference.
This circuit works for most digital modes but will not allow CW transmission. For that you will also need a "QSK" circuit which is another simple maker project. Note that there is no hardware signal level control in this circuit. I use software level control in my PC. In Linux systems you can set audio levels with "Alsamixer" from a terminal command. I quit Windows many years ago but I believe it has a similar sound level control app.
Attached is a picture of my Poor Ham's Signalink. The Hammond aluminum project box has been re-used from a previous version that used a serial port for PTT control so it looks a little scruffy. If you decide to build your own and need help just let me know.
John, VA3KOT