Introduction to Data Modes

1. Introduction to Data Modes Mike Richards G4WNC

2. The Menu • Data Modes - Why Bother? • Data Modes Flow Chart • Technical bits. Data – Alphabets – Error Correction – Modulation • Practical Systems - PSK-31 • Practical Systems - V4Chat • Summary & Questions Mike Richards - Introduction to Data Modes (HFC 2011)

3. Data Modes - Why Bother? • Self Education • A new dimension to your radio operating • Efficient use of spectrum • Can be good for DX • You can do it for free! Mike Richards - Introduction to Data Modes (HFC 2011)

4. Data Modes - Overview Encoding Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet conversion Alphabet conversion Error protection Error correction Tone decoder Tone generation R A D I O L I N K Decoding Mike Richards - Introduction to Data Modes (HFC 2011)

5. Keyboard to Serial Data A Keyboard ASCII 65 128 64 32 16 8 4 2 1 0 1 0 0 0 0 0 1 Serial data 0 1 0 0 0 0 0 1 Mike Richards - Introduction to Data Modes (HFC 2011)

6. Data Modes - Alphabets Encoding Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet conversion Alphabet conversion Error protection Error correction Tone decoder Tone generation R A D I O L I N K Decoding Mike Richards - Introduction to Data Modes (HFC 2011)

7. Alphabets • Why change the alphabet? • RTTY - limited to 5 bits • PSK31 – uses Varicode • Amtor & Pactor – error detection code Mike Richards - Introduction to Data Modes (HFC 2011)

8. Data Modes - Errors Encoding Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet conversion Alphabet conversion Error protection Error correction Tone decoder Tone generation R A D I O L I N K Decoding Mike Richards - Introduction to Data Modes (HFC 2011)

9. Dealing with errors – 1: SSB • Ignore • Rely on distant operator to work-out errors • Repeat • Say everything twice • Short messages and confirm • Bit at a time and confirm each transmission • Use phonetics • Add more information to get through Mike Richards - Introduction to Data Modes (HFC 2011)

10. Dealing with errors – 2: Data Modes • Repeats • Used in simple FEC – 3 characters at a time, delayed by 3 characters • Automatic Repeat Request (ARQ) • Send short bursts and await confirmation • Forward Error Correction • Add extra information Mike Richards - Introduction to Data Modes (HFC 2011)

11. Dealing with Errors – 3: Repeats Simple Forward Error Correction Original text Repeated text Transmitted text ~ = Data padding Used for AMTOR FEC and NAVTEX marine safety system Mike Richards - Introduction to Data Modes (HFC 2011)

12. Dealing with Errors – 4: Automatic Repeat Request (ARQ) • Send data in short bursts • Wait for acknowledgement • Repeat on request Data 1 Data 2 Data 3 Data 2 Originator ACK ACK ACK ARQ Distant Stn • Very reliable • Excellent with deep QSB • Say everything once • Only handles 1:1 QSOs • Amtor, Pactor, Packet Mike Richards - Introduction to Data Modes (HFC 2011)

13. Dealing with Errors – 5: Forward Error Correction (FEC) • Convolutional Coding • Digital version of phonetics • NASA Voyager algorithm • 2 bits out for each 1 input • Output pattern dependent on previous 6 bits • Rate ½ constraint 7 • Used in MFSK16, ROS, WINMOR, V4Chat, QPSK31, JT65A • Walsh functions • Used in Olivia and MT63 1 0 1 0 1 0 1 0 Rate ½ constraint 3 encoder 10 01 01 10 00 11 11 00 Mike Richards - Introduction to Data Modes (HFC 2011)

14. Data Modes – Modulation Systems Encoding Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet Conversion Alphabet conversion Alphabet conversion Error protection Error correction Tone decoder Tone generation R A D I O L I N K Decoding Mike Richards - Introduction to Data Modes (HFC 2011)

15. Simple Modulation Systems - FSK Frequency Shift Keying (FSK) 1 Original Data 0 +170Hz Carrier Frequency fc Audio Frequency Shift Keying (FSK) 1445Hz Audio Tones 1275Hz Mike Richards - Introduction to Data Modes (HFC 2011)

16. Simple Modulation Systems - PSK Phase Shift Keying (PSK) 1 Original Data 0 180 Carrier phase 0 Mike Richards - Introduction to Data Modes (HFC 2011)

17. Practical Systems – PSK31 • Custom designed for keyboard QSOs • Narrow bandwidth - just 31Hz • Entire 20m activity in one speech channel! • Perfect for normal typing speeds • No error correction – keeps it simple • Most popular mode • Can always find activity Mike Richards G4WNC- Introduction to Data Modes (HFC 2011)

18. PSK-31 with DigiPan Mike Richards - Introduction to Data Modes (HFC 2011)

19. Practical Systems V4Chat • Brand new mode in development • Modern AMTOR replacement • Includes FEC and ARQ modes • Derived from the V4 Terminal Node Controller • Activity centred on 14073kHz Mike Richards - Introduction to Data Modes (HFC 2011)

20. V4Chat in action Mike Richards - Introduction to Data Modes (HFC 2011)

21. Tips & Questions • Choose the right mode • Keep the power down • Don’t over modulate • Avoid stored text – talk to people • Give useful signal reports • Have a go – it’s fun • Any Questions? • Don’t forget to pick-up a handout Mike Richards - Introduction to Data Modes (HFC 2011)