PSK31 interface

MØKGK Amateur Radio Pages

PSK31 Interface, last updated 2018-11-13

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PSK31 Interface

This mode is something I've taken an interest in recently, the ability to get good distances with low power is one of the features of this digital mode. In summary PSK31 is a phase shifted (0°/180°) carrier to convey the 1's and 0's of digital information at a rate of 31.25 baud. There are extra tweaks so that commonly used characters occupy shorter sequence lengths. It's possible to fit dozens of QSO's into the space occupied by a single SSB transmission.

If you have a PC near to the operating position, one of the painless ways to get on PSK31 is to interface a PC to the transceiver and use one of the multitude of free and shareware packages out there to perform the encoding and decoding functions. Here's a simple interface I built for the PC based on one built by my father GM4KGK.

	This is the circuit diagram, you will need to click on the picture to see a full size version. It uses cheap audio transformers to isolated the PC sound card input and output from the transceiver. The Icom 735 has a handy accessory socket on the back into which this all plugs. RTS and DTR from the serial port turn the transmitter on and off using opto isolators - I've added a facility to key the morse input if I decide to use the PC keyboard in future to generate CW.
	The whole lot goes into a plastic box, visible are the two audio transformers and sockets for the opto isolators placed on a small piece of stripboard. It should be kept well away from RF and mains, this one sits on the top of the PC case.
	A much more pleasant view of the level controls and the two leds which indicate the activity of the unit.
	Setup in the makeshift shack, the PSK31 interface can just be seen on the top of the PC case. Software in use is Digipan which works well. The scope doesn't normally live under the screen, but was handy for setting the unit up!

It should be fairly cheap to knock up something like this. Even the pots are optional if you want to tweak the levels through the soundcard controls.

In addition to PSK31, the unit has been successfully used to receive SSTV transmissions. I'll try it out on RTTY and a few other modes - will update the page when I have the results...

UPDATE: After only a week of use, this little box has worked 22 DXCC countries on PSK31, PSK63 and QPSK. I plan to make a new one with everything on a proper PCB and will amend it to make use of the CAT facilities of the Icom 735 for frequency control in addition to controlling audio, TX/RX and the CW key input.