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Digital Modes

Digital Modes. RTTY, PSK31 , Packet, Pactor, Clover, Hellschreiber, MFSK, G-TOR, MT-63, Throb, Q15X25. PSK 31. Cousin of RTTY Excellent weak-signal performance Not error free. History. Created by Peter Martinez, G3PLX At first, not very popular because special DSP hardware was needed.

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Digital Modes

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  1. Digital Modes RTTY, PSK31, Packet, Pactor, Clover, Hellschreiber, MFSK, G-TOR, MT-63, Throb, Q15X25

  2. PSK 31 • Cousin of RTTY • Excellent weak-signal performance • Not error free

  3. History • Created by Peter Martinez, G3PLX • At first, not very popular because special DSP hardware was needed. • 1999 - Peter designed a version of PSK31 that needed nothing more than a common computer sound card.

  4. History • Simple piece of software that ran under Windows. • Software available free on Internet • Uses soundcard interface to the transceiver.

  5. History • PSK31 exploded in the HF digital community. • Most popular mode for casual QSO’s. • PSK63 appeared in 2003 and is used by contesters.

  6. What is PSK31? • PSK = Phase Shift Keying • 31 = bit rate (31.25 baud) =========================== • Compare to CW • Simple binary code • Short pulses (Dits) • Long pulses (Dahs) • Communicate the whole English language by combining strings of dits and dahs. • Gaps separate characters and words.

  7. Compared to RTTY • Still binary • Instead of on/off (CW), shift frequencies (FSK) • 5 bits plus start and stop pulses. • PSK uses Varicode • Varying number of bits representing each character. • Shorter for often used characters • Longer for less often used characters

  8. The letter “e” is used most often and gets a Varicode of 11, whereas, “E” gets a Varicode of 1110111 • “z” gets very little use so it has a Varicode of 111010101; “Z” gets 1010101101 • Gaps represented by “00” • Two zeros never get used in characters

  9. A Digital Station • What is needed? • Transceiver – most already have one. • Modem – many have them in the form of a computer soundcard. • Software – converts binary data from computer to modulated audio tones.

  10. A Digital Station • Interface – the connection between the computer soundcard and the transceiver. • Audio from soundcard to transceiver • Audio from transceiver to soundcard • PTT

  11. Interface • Numerous available on the market • Rigblaster

  12. Interface • RigExpert SD Standard Plus

  13. Interface • Tigertronics SignaLink SL-1+ USB

  14. Interface • Buxcomm Rascal GLX

  15. Interface • Homebrew

  16. Interface • NUE-PSK Digital Modem • A digital modem for PSK31 field operation ... without using a PC! • The NUE-PSK Digital Modem comes fully assembled and tested... just plug in your keyboard and SSB transceiver, and start operating! • www.amqrp.org

  17. How do we generate BPSK signal and transmit Varicode over the airwaves? • Use DSP capabilities of soundcard • Create audio signal that shifts phase angle 180 degrees in sync with 31.25 bps data stream • “0” bit generates phase shift • “1” bit does not • Hence, Binary Phase-Shift Keying

  18. When the BPSK audio signal is applied to an SSB transceiver we get BPSK modulated RF. • Only 31.25 Hz wide, narrower than CW. • Concentrating RF into narrow bandwidth produces good reception. • Receiving station must sync with transmitting station (Software) • Phase transitions are mathematically predictable due to the structure of Varicode.

  19. PSK31 Software • Download off Internet: • Many are freeware or shareware with a requested donation. • Popular programs: • HRD/DM780 (IMHO, the best) • MixW • Digipan • MultiPSK • Others

  20. PSK31 Setup • Receiving (You should be hearing a PSK warbling sound. If not, check your sound card volume) • Panoramic display – waterfall • With no IF or AF filtering the bandwidth on the waterfall is about 3000Hz. • Bandwidth of BPSK signal is 31Hz. • Many PSK signal can fit in that spectrum • Vertical lines of varying color/intensity will be seen on the waterfall • Bright = strong, faint = weaker

  21. ACTIVITY • PSK31 activity found on: • 160M 1807 kHz (USA) 1838 kHz (Europe) • 80M 3580 kHz • 40M 7070 kHz (USA) 7035 kHz (Europe) 7028 kHz (Japan) • 30M 10138-10142 kHz(Digital Only) • 20M 14070 kHz – most activity • 17M 18100 kHz • 15M 21070 kHz • 12M 24920 kHz • 10M 28120 kHz • 6M 50290 kHz (USA) 50250 kHz (Europe) • Let’s get started…

  22. Park radio on frequency of your choice. • Frequency displayed is Suppressed Carrier Frequency (SCF) • USB – range is 2-3 kHz above SCF. • LSB – range is 2-3 kHz below SCF. • Example: Radio showing 14070 kHz USB • Receiving everything from 14070 to 14073 kHz. • Place cursor on vertical signal line and click. • Software selects and decodes the signal. • When you transmit, the software will generate a tone (warble) corresponding to the frequency of the selected tone.

  23. Transmitting • Tone selected creates an RF signal on the correct frequency. • PSK31 is a 80-100% duty cycle mode. • Most operators run a 20-40% of maximum output. • Power level is adjusted by the level of the audio signal being fed to the input. • Most accepted procedure: • Set Power to max. (100W for most TRX) • Apply signal to audio input • Adjust level to 20-40% (20-40W) • Overdriving will cause splatter making your signal much wider than 31 Hz.

  24. Overdriving • Indications • ALC will show activity. There should be no ALC indications. • Goal is to stay in the linear portion of the operating curve. • Some radios will become non-linear at 50% max. • This is not as noticeable with SSB voice signals • Shows up as splatter in PSK31 mode. • Use IMD (Intermodulation Distortion) meter • Good signal shows IMD of <-20 db • Ideally, <-23 • Overdriving can alsoburn out you final transistors

  25. W8KRF PSK Station

  26. Digital Signal Reporting • RSQ Reporting • Readability • Strength • Quality • Although not yet accepted in Region 2, it has been in Regions 1 & 3 and it is being used by some stations in the US. • It more accurately indicates the quality, as well as, strength of the PSK signal. • Go to www.rsq-info.net for more informaiton.

  27. Readability • R5 95%+ Perfectly readable • R4 80% Practically no difficulty, occasional missed characters • R3 40% Considerable difficulty, many missed characters • R2 20% Occasional words distinguishable • R1 0% Undecipherable • Strength • S9 Very strong trace • S7 Strong trace • S5 Moderate trace • S3 Weak trace • S1 Barely perceptible trace • Quality • Q9 Clean signal – no visible unwanted sidebar pairs • Q7 One barely visible pair • Q5 One easily visible pair • Q3 Multiple visible pairs • Q1 Splatter over much of the spectrum

  28. Resources • ARRL’s HF Digital Handbook, Third Edition by Steve Ford, WA8IMY • Websites: • www.westmountainradio.com • www.rigexpert.com • www.tigertronics.com • www.buxcomm.com • www.geocities.com/n2uhc/interface.html • http://forums.ham-radio.ch/ (HRD)

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