PSK31 A Basic Application By James C. Hall WB4YDL Reelfoot Amateur Radio Club April 22, 2004
PSK31 Background Developed by Peter Martinez, G3PLX The fastest growing digital mode worldwide Similar to RTTY – keyboard to keyboard QSO’s Bit rate is the same as bandwidth – 31.25 Hz Well suited to sound card 8 kHz sampling –8000 Hz ÷ 256
PSK31 Concepts Frequency Shift Keying (FSK) used in RTTY where the ‘mark’ (1) and ‘space’ (0) are different frequencies Space Mark
PSK31 Concepts Phase Shift Keying (PSK) defines a zero (space) as a 180° phase reversal and a one (mark) as in phase with a reference frequency
PSK31 Concepts Keeping the Bandwidth Narrow The problem with phase reversal is broadband splatter Solution: Gradually reduce the signal amplitude to zero at phase reversal No need to reduce amplitude without phase reversal
PSK31 Concepts Performance RTTY uses ASCII 8 bits with start and stop bits for each character PSK31 Brightness For SSB, 100 watts in a 3 kHz bandwidth = 30 mwatts/Hz For PSK31, 100 watts in a 31 Hz bandwidth = 3200 mw/Hz This is > 100 times brighter (or 20 dB) than SSB Much less power needed in PSK31 for the same S/N ratio PSK31 is ideal for QRP with cross-country QSO’s common with 1 watt ! High S/N ratio = less bit error PSK31 use Varicode Variable coding Most common characters use the fewest bits Average number of bits per character is about 6.5 Improves data rate for the same bandwidth
Sound Card Digital Modes Connecting your Radio to your Computer CW PSK31 RTTY PACKET APRS FSK411 JT44 EME You can purchase an interface to connect your transceiver to your computer, OR you can make your own for a few $.
Sound Card Digital Modes Connecting your Radio to your Computer Receive Audio Connection: CW PSK31 RTTY PACKET APRS FSK411 JT44 EME Connect an audio cable between the transceiver audio output and the soundcard LINE IN jack.
Sound Card Digital Modes Connecting your Radio to your Computer Transmit Audio Connection: CW PSK31 RTTY PACKET APRS FSK411 JT44 EME Connect a shielded audio cable between the transceiver MIC input and the soundcard LINE OUT jack through a 40 db attenuator. If your transceiver has a LINE input, no attenuation is required. (eliminate the 2 resistors)
Sound Card Digital Modes Connecting your Radio to your Computer T/R Connection: CW PSK31 RTTY PACKET APRS FSK411 JT44 EME PTT is controlled via the RTS and/or DTR outputs of the computer’s RS-232 serial port.
Basic PSK31 Station HF Transceiver Computer Sound Card COM Port PSK31 Application Speaker Out Line In Line Out Mic Input DTR or RTS of COM n Antenna
PSK31 Conclusions PSK31 is great for you if … You want to try a new mode without a big investment Enjoy digital modes Enjoy ragchewing Enjoy chasing DX Enjoy software and computers Enjoy QRP Enjoy kit building Have a marginal antenna, low power, or poor location Want to stay on the cutting edge 73 de Jamie WB4YDL