PSK31PSK31A Basic ApplicationA Basic Application

By James C. Hall WB4YDL

Reelfoot Amateur Radio ClubReelfoot Amateur Radio Club

April 22, 2004

PSK31 BackgroundPSK31 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 ConceptsPSK31 Concepts

Frequency Shift Keying (FSK) used in RTTY where the ‘mark’ (1) and ‘space’ (0) are

different frequencies

Space

Mark

PSK31 ConceptsPSK31 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 ConceptsPSK31 ConceptsKeeping the Bandwidth NarrowKeeping 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 ConceptsPSK31 ConceptsPerformancePerformance

• 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 ModesSound Card Digital Modes

Connecting your Radio to your ComputerCW

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 ModesSound Card Digital Modes

Connecting your Radio to your ComputerCW

PSK31

RTTY

PACKET

APRS

FSK411

JT44

EME

The KK7UQ sound card interface kit packaged in an Altoids© tin

Sound Card Digital ModesSound 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 ModesSound Card Digital ModesConnecting your Radio to your

ComputerTransmit 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 ModesSound Card Digital ModesConnecting 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 PTT is controlled via the RTS and/or DTR outputs of the computer’s RS-232 serial port.computer’s RS-232 serial port.

Basic PSK31 StationBasic 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 ConclusionsPSK31 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