Prepared by Carl Ferguson, W4UOA January 2001

PSK31

Prepared by Carl Ferguson, W4UOA January 2001

PSK31Background

• Digital mode designed by Peter Martinez, G3PLX, • based on the RTTY mode of operation, and• intended for live keyboard to keyboard QSOs.• Offers an effective speed of 50wpm, and• exceptionally well suited to QRP.• PSK31 will not make Pactor, Pactor-2, Clover-II or

Gtor obsolete.• PSK31 does not offer error free communications.

Prepared by Carl Ferguson, W4UOA January 2001

PSK31 ConceptsIntroduction

• The 128 ASCII character set is digitally Varicoded.

• Like Morse Code, varicodes allocates the shorter codes to the more-common characters.

Prepared by Carl Ferguson, W4UOA January 2001

PSK31 ConceptsVaricodes

32 (SP) 1a 1011e 11i 1101o 111u 11011

ASCII Varicode

Prepared by Carl Ferguson, W4UOA January 2001

PSK31 ConceptsSpeed and Bandwidth

• With an average of 6.5 bits per character, a bit rate of about 32 bps to transmit at about 50 words per minute requires.

• Martinez chose 31.25 bps because it can be easily derived from the 8-KHz sample-rate used in many DSP systems.

• In theory, a bandwidth of only 31.25 bps would be required.

Prepared by Carl Ferguson, W4UOA January 2001

PSK ConceptsModulation

Instead of frequency-shifting the carrier, which is wasteful of spectrum, or turning the carrier on and off, which is wasteful of transmitter power capability, the dots of the code are signaled by reversing the polarity of the carrier. The method is thought to have been first used by SP9VRC.

PSK31: A New Radio-Teletype Mode, Peter Martinez, G3PLX, QEX, July/August 1999

Prepared by Carl Ferguson, W4UOA January 2001

PSK ConceptsBinary Phase-Shift Keying

G3PLX called this polarity-reversal keying, saying,

“You can think of this as equivalent to transposing the wires to your antenna feeder. This uses the transmitted signal more efficiently since we are comparing a positive signal before the reversal to a negative signal after it, rather than comparing the signal present in the dot to no-signal in the gap.”

PSK31: A New Radio-Teletype Mode, Peter Martinez, G3PLX, QEX, July/August 1999

Prepared by Carl Ferguson, W4UOA January 2001

PSK ConceptsDemodulation

The phase transitions of a BPSK-modulated signal are easy to recognize – even when they are deep in the noise – because the demodulator knows when to expect them. The receiving station synchronizes with a short idle string of 0s sent at the beginning of every transmission. Varicode phase transitions are also mathematically predictable, so much so that the PSK31 software can quickly synchronize itself when you tune in during the middle of a transmission, or after you momentarily lose the signal.

Prepared by Carl Ferguson, W4UOA January 2001

The Sounds of PSK31

This is a PSK signal sending CQ.

Prepared by Carl Ferguson, W4UOA January 2001

PSK OperationSplatter

The fading lines to the right and left of the primary signal areintermod – splatter – usually the result of over-driving the sound card or transmitter.

Sound output and mike gain interact. As a general rule, set the mike where you would normally operate and then adjust the computer sound output until you see no ALC activity.

Prepared by Carl Ferguson, W4UOA January 2001

BPSK Signal

Prepared by Carl Ferguson, W4UOA January 2001

PSK31 vs AMTOR/PACTOR

Prepared by Carl Ferguson, W4UOA January 2001

PSK31 Links

• http://aintel.bi.ehu.es/psk31.html “PSK31 Official Homepage”an excellent source for background information

• http://www.qsl.net/wm2u/psk31.htmla good source of additional information and links to most of the free PSK31 application software

Prepared by Carl Ferguson, W4UOA January 2001

PSK31 Links

• http://www.arrl.org/tis/info/psk31.htmlgood reference material and links

• http://www.smallwonderlabs.com/good source for kits and technical information

Prepared by Carl Ferguson, W4UOA January 2001

PSK31 Links

• http://members.home.net/hteller/digipan/Howard (Skip) Teller’s DigiPan Home Page

• http://members-proxy-3.mmbrprxy.home.net/hteller/psk31pictures/

pictures via PSK31

Prepared by Carl Ferguson, W4UOA January 2001

Marker

Prepared by Carl Ferguson, W4UOA January 2001

The over

Idle

Note the clean edges of the signal.

Prepared by Carl Ferguson, W4UOA January 2001

Offset from base frequency

Note offset of 1,100 Hz

Prepared by Carl Ferguson, W4UOA January 2001

Look at the number of QSOs between 1,000 and 2,000 Hz?

Prepared by Carl Ferguson, W4UOA January 2001

Notice the markers now show actual frequency, not offset.

Prepared by Carl Ferguson, W4UOA January 2001

An exchange with PA3ENH. I may have had the audio gain too high. Notice blue background in the waterfall. His signal was VERY weak.

Prepared by Carl Ferguson, W4UOA January 2001

Prepared by Carl Ferguson, W4UOA January 2001

Prepared by Carl Ferguson, W4UOA January 2001

Prepared by Carl Ferguson, W4UOA January 2001

Prepared by Carl Ferguson, W4UOA January 2001

Prepared by Carl Ferguson, W4UOA January 2001

Prepared by Carl Ferguson, W4UOA January 2001

Prepared by Carl Ferguson, W4UOA January 2001

Prepared by Carl Ferguson, W4UOA January 2001

Prepared by Carl Ferguson, W4UOA January 2001

Prepared by Carl Ferguson, W4UOA January 2001

Good example of splatter!

Prepared by Carl Ferguson, W4UOA January 2001

Simple Phone Patch Hookup

Transceiver

Patch-In Patch-Out

Sound Card

Line-In Line-Out

•Download and install software, e.g. DigiPan or Zakanaka

•Cable phone patch to sound card

•Setup the transceiver for VOX

•Start with RF gain at maximum and AF gain at minimum

•Set line-in and line-out audio controls at the center position

•Configure software and code macros of your choice