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Test Slide Data Modes – Starting Out Mike Richards G4WNC.

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Presentation on theme: "Test Slide Data Modes – Starting Out Mike Richards G4WNC."— Presentation transcript:

1

2 Test Slide

3 Data Modes – Starting Out Mike Richards G4WNC

4 The Menu Data Modes - Why Bother? Data Modes Flow Chart Technical bits. What You Need Operating Summary & Questions 6th Sept 2012 Mike Richards – Data Modes – Starting Out (RSGB 2012) 3

5 Data Modes - Why Bother? Self Education A new dimension to your radio operating Efficient use of spectrum Great for QRP and DX You can do it for free! 6th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 4

6 Data Modes - Overview 12th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 5 Encoding Decoding

7 A UNICODE(ASCII) 65 Keyboard Serial data Keyboard to Serial Data 6th Sept Mike Richards - Introduction to Data Modes (RSGB 2012)

8 Data Modes - Alphabets 6th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 7 Encoding Decoding

9 Alphabets - 1 What alphabet? – Code used to represent letters in text Why change the alphabet? – RTTY Old system uses 5 bits for each character Adds a start bit and 1.5 – 2 stop bits Wraps-up each character 6th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 8

10 Alphabets - 2 Why change the Alphabet? – PSK31 Uses Varicode – Common letters have short codes – Less common have longer codes – Space = 1, e = 11, o = 111, z = – Provides faster message speed on low speed links – Ideal for typed QSOs and text messages 12th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 9

11 Data Modes - Errors 12th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 10 Encoding Decoding

12 Dealing with errors – 1: SSB 6th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 11 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

13 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 6th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 12

14 Dealing with Errors – 3: Repeats HELLO 6th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 13 Original text Repeated text Transmitted text HELLO H~E~LHLEOL~L~O~ ~ = Data padding Used for AMTOR FEC and NAVTEX marine safety system Simple Forward Error Correction

15 Dealing with Errors – 4: Automatic Repeat Request (ARQ) 6th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 14 Originator Distant Stn Data 1Data 2 ACK ARQ Data 2Data 3 Send data in short bursts Wait for acknowledgement Repeat on request Very reliable Excellent with deep QSB Say everything once Only handles 1:1 connections Winmor, Pactor, Packet

16 Dealing with Errors – 4 Forward Error Correction (FEC) 6th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 15 Convolutional Coding – Digital version of phonetics – NASA Voyager algorithm 2 bits out for each 1 input Output pattern dependent on the 7 bits in the coder – Used in MFSK16, ROS, WINMOR, V4Chat, QPSK31, JT65A Walsh functions – Used in Olivia and MT Simple Convolutional Coder

17 Data Modes – Modulation Systems 6th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 16 Encoding Decoding

18 Simple Modulation Systems - FSK 6th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 17 Frequency Shift Keying (FSK) +170Hz Carrier Frequency 1275Hz 1445Hz Audio Tones Audio Frequency Shift Keying (AFSK) fc Original Data 0 1 RTTY

19 Modulation Systems - MFSK 12th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 18 Olivia – Multi Frequency Shift Keying Used in many complex modes Uses multiple shifts typically 16 or 32 Time f1 f2 f3 f4 f5 f6 f7 f8

20 Simple Modulation Systems - PSK 6th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 19 Phase Shift Keying (PSK) Carrier Phase Original Data 0 1 In PSK31 a logic 0 causes a phase reversal

21 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 23rd Sept 2012 Mike Richards G4WNC- Introduction to Data Modes (RSGB 2012) 20

22 Practical Systems - RTTY Still survives! Fast and Simple Used extensively in contests 20m good starting band 6th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 21

23 Data Modes Operation – Get Going What do you need: – PC with a sound card Windows XP (or later), Linux, Mac Digital Modes Software FLDIGI or sim. – SSB transceiver and Antenna – Two screened leads for audio in and out Optional interface unit 12th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 22

24 Data Modes – Connections 12th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 23 Computer Sound Card Line out Mic in SSB Transceiver Line in Audio out Optional PTT SignalLink Interface Line out Mic in SSB Transceiver Line in Audio out USB PTT

25 Data Modes – Operating Tips Listen first Start with PSK-31 – always activity on 20m Use low power – 5 watts is usually plenty Watch your modulation Keep to the band plans Use short CQ calls Give real RST reports Try conversing! 12th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 24

26 Questions Have a go – it’s fun Any Questions? Don’t forget to pick-up a handout 6th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 25


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