Transcript PSK31 - Reelfoot ARC

Reelfoot Amateur Radio Club
PSK31
A Basic Application
By James C. Hall WB4YDL
April 22, 2004
PSK31 Background
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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
Mark
Space
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
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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
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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
• 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
Sound Card Digital Modes
CW
Connecting your Radio to your
Computer
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
CW
PSK31
RTTY
PACKET
APRS
FSK411
JT44
EME
The KK7UQ sound card interface kit packaged in an Altoids© tin
Sound Card Digital Modes
CW
PSK31
Connecting your Radio to your
Computer
Receive Audio Connection:
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
CW
PSK31
Connecting your Radio to your
Computer
Transmit Audio Connection:
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
CW
PSK31
Connecting your Radio to your
Computer
T/R Connection:
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
Speaker
Out
Computer
Line In
Sound Card
Line Out
Antenna
COM Port
PSK31
Application
DTR or RTS of COM n
Mic
Input
HF Transceiver
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