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Digital Communications

Digital Communications. El Paso Amateur Radio Club August 22, 2003 Tom, WB5QLR. Repeat Offender – 8/9/00. Digital Modes. RTTY PSK31 PSK63 MFSK WSJT. Computer Based. Hardware requirements SoundBlaster compatible sound card PC capable of running Win95/98 PTT switching mechanism.

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Digital Communications

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  1. Digital Communications • El Paso Amateur Radio Club • August 22, 2003 • Tom, WB5QLR

  2. Repeat Offender – 8/9/00

  3. Digital Modes • RTTY • PSK31 • PSK63 • MFSK • WSJT

  4. Computer Based • Hardware requirements • SoundBlaster compatible sound card • PC capable of running Win95/98 • PTT switching mechanism

  5. Computer Based • Software • Software for mode of operation • Might have multiple mode in same program

  6. What is NOT Necessary • Heavy teletype • TNC • Special tuning scopes

  7. Main Point #1 • Digital modes can be implemented totally with: • Computer • Sound Card • Software • Simple PTT circuit from serial port

  8. Connections • Receiver audio out into Computer line in • Preferable if audio out is independent of AF gain • Could also run through a 1:1 audio transformer to help isolate grounds

  9. Connections • Computer speaker in Transmitter audio • Use a resistor and 1:1 audio transformer • Optional trimmer pot to control audio level

  10. Audio Connection

  11. Connections • Computer serial port to Transmitter PTT • Circuit includes: • 1 resistor • 2 diodes • 1 transistor • Optional DPST to switch between 2 inputs from serial port

  12. PTT Connection

  13. RigBlaster Interface

  14. RigBlaster Interface - Back

  15. RTTY • Convention is LSB • Been around for a long time

  16. RTTY

  17. PSK and sound • Convention is USB • Most around 14.070 MHz and up • Phase shifted • Variable code – combination of Baudot and Morse • Band width is 31.25 cycles wide • Efficiency ranks with CW • Implemented completely with sound card and software

  18. PSK Tuning – Old Style

  19. PSK Tuning – New Style

  20. PSK Tuning – New Style

  21. PSK Frequencies • 3.580 MHz • 7.080 MHz • 10.140 MHz • 14.070 MHz • 18.100 MHz • 21.080 MHz • 28.120 MHz

  22. PSK 63 • 100 wpm character transmission speed for contest exchanges and macro transmission versus RTTY at 60 wpm • Only 1/5 the bandwidth of RTTY - capable of displaying 24 signals simultaneously on a waterfall or spectrum display • Capable of color thumbnail portrait transmission in less than 2 minutes • Faster sync recovery than RTTY, resulting in fewer errors

  23. PSK 63 • Requires much less power than RTTY for the same communications performance • Identical to PSK31 except for a wider bandwidth of 63 Hz • Improved polar path performance compared to PSK31 • Works with any soundcard-equipped Windows computer and SSB transceiver • High-speed transmission of macros and brag files

  24. MFSK – Mutiple Frequency Shift Keying • A Weak signal digital mode • Advantages • High rejection of pulse and broadband noise due to narrow receiver bandwidth per tone • Low baud rate for sensitivity and multi-path rejection - data bit rate higher than symbol baud rate • Constant transmitter power • Tolerance of ionospheric effects such as doppler, fading and multi-path

  25. MFSK • Disadvantages • Narrow spacing and narrow bandwidth of the individual tone detectors • Drift can be a problem and accurate tuning is essential.

  26. WSJT – Weak Signal by W1JT • Four Modes • FSK441 – Meteor Scatter • JT6M – Meteor Scatter for 6M • JT44 – Tropo and EME • EME Echo – Listening to your EME return • Competitive with 50 watts and 10-11 element beam

  27. Bandpass Comparisons

  28. Resources • RTTY/PSK software • TrueTTY - www.dxsoft.com • 3KHz band pass • On RTTY, both FSK and AFSK • RigBlaster Interface • www.westmountainradio.com/RIGblaster.htm

  29. Resources • PSK Home Page • www.aintel.bi.ehu.es/psk31.html • PSK only software • DigiPan – www.digipan.net • WinPSKse - www.winpskse.com • Other Sites • Great overview - www.qsl.net/kk7lk/psk31.htm • Interface details - www.w5bbr.com/psk31.html

  30. Resources • MSFK • http://www.qsl.net/zl1bpu/MFSK/ • Software – Stream - http://iz8bly.sysonline.it/Stream/index.htm • WSJT • http://pulsar.princeton.edu/~joe/K1JT/ • http://www.qsl.net/wa5ufh/WSJTGROUP/WSJTGROUP.htm • Ping Jockey - http://www.pingjockey.net/cgi-bin/pingtalk

  31. Resources • Articles • QST May, 1999 pg 41-44 • QST May, 2000 pg 42-45 • Book • ARRL’s HFDigital Handbook

  32. Non Digital Resources • Logging software • XMLog - www.xmlog.com • Multiple logs books • Easy reference to notes • Logger - www.qsl.net/kc4elo/ • Little higher level • Includes PSK • Contesting Software – www.writelog.com • Includes RTTY and PSK

  33. Main Point #2 • Fun • Easy • On air demonstration • Slides and references at www.striplingdata.com/w5es

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