Slide 1

Slide 2 Test Slide Slide 3 Complex Data Modes for Beginners Mike Richards G4WNC Slide 4 The Menu for Today Complex Data Modes What & Why? Process Flow Chart Technical bits. What You Need Operating Summary & Questions 6th Sept 2012 Mike Richards Complex Data Modes (RSGB 2012) 3 Slide 5 Complex Modes What & Why? What are complex modes? Digital communication systems that have been designed to be more reliably than simple modes Why bother? Self Education A new dimension to your radio operating Facilitates operating under poor conditions Great for QRP and DX You can do it for free! 6th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 4 Slide 6 Complex Modes - Overview 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 5 Slide 7 Data Modes Data Preparation 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 6 Slide 8 A UNICODE(ASCII) 65 Keyboard 00100001 1286432168421 Serial data 01000001 Keyboard to Serial Data 6th Sept 20127 Mike Richards - Complex Modes (RSGB 2012) Slide 9 Complex Modes Channel Coding 6th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 8 Encoding Slide 10 Channel Coding -1 Adapt the message to suit the link Add error detection and or protection Two link categories 1:1 link supporting duplex operation Real time communications in both directions Supports Automatic Repeat Request (ARQ) Broadcast Unidirectional link Requires Forward Error Correction (FEC) 6th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 9 Slide 11 Dealing with errors 1: Speech Signals 6th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 10 Ignore Rely on distant operator to work-out errors Repeat Say everything twice Short messages and confirm Word at a time and confirm receipt Use phonetics Add more information to get through Slide 12 Dealing with errors 2: Data Modes In data modes we use: Automatic Repeat Request (ARQ) Send short data bursts and await confirmation Forward Error Correction (FEC) Add extra information to enable the receive station to recover a damaged message 6th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 11 Slide 13 Channel Coding - Automatic Repeat Request (ARQ) 6th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 12 Originator Distant Stn Data 1Data 2 ACK ARQ Data 2Data 3 Send data in short bursts Wait for acknowledgement Repeat on request Slide 14 Channel Coding ARQ Pros: Can be very reliable and great for QRP Excellent with deep QSB Type everything once system handles the repeats Used by Winmor, V4Chat, Amtor, Pactor, Packet Cons: Often slow Protracted repeats under poor conditions Only caters for 1:1 connections 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 13 Slide 15 Channel Coding - FEC FEC Most commonly used form of error correction Adds information to the message Phonetics for digital Known as redundancy Very powerful NASA use these techniques to recover data from space probes 11 billion miles away! 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 14 Slide 16 Channel Coding Simple FEC HELLO 6th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 15 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 Slide 17 Channel Coding - FEC Simple FEC very limited Require a more sophisticated solution NASA Voyager space program Developed a system using convolutional coding Very powerful Produces an output that is the result of processing the 7-bits currently in the coder 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 16 Slide 18 Channel Coding FEC Convolutional Coding 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 17 1000000 0100000 0010000 000100000001000000010 00000010000000 Clock pulse 0000000 Uses flip-flops or shift registers Each clock pulse moves the input data to the output 7-bits contained within the coder = constraint Slide 19 Channel Coding Convolutional Coding Extract two outputs from the coder Each bit entering produces 2-bits out = Rate Simple model with constraint 3 and rate 1/2 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 18 Flip-flop 1 0 0 1 1 0 0 01 0 1 1 1 1 0 1 11 0 0 1 1 1 1 1 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 Slide 20 Channel Coding Convolutional Coding Summary 6th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 19 Creates a pattern from all the bits within the coder Defined by Constraint (k) and Rate (Input bits/Output bits) NASA Voyager algorithm most common K = 7 rate = Used in MFSK16, ROS, WINMOR, V4Chat, QPSK31, JT65A Slide 21 Channel Coding Walsh functions 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 20 Walsh function Alternative coding system Used in Olivia and MT63 Each 7-bit ASCII character produces a 64-bit output Slide 22 Complex Modes Modulation Systems 6th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 21 Encoding Slide 23 Complex Modes - Modulation We have a protected data stream What else can we do to ensure safe transit? Decoding systems dont like high levels of consecutive bit errors Spread data in both frequency and time 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 22 Slide 24 Complex Modes - Modulation Frequency Spreading Most modes do this Employs multiple tones Bandwidth up to 2kHz Contentious? 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 23 Slide 25 Complex Modes - Modulation Frequency spreading example Olivia uses 32 tones in a 1000Hz bandwidth 32 tone combinations = 0-31 in binary = 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 24 1111 142816 1 = 5-bits per tone (Symbol) Slide 26 Complex Modes - Modulation 12th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 25 MFSK simple 8-tone example Time f1 f2 f3 f4 f5 f6 f7 f8 Olivia 32/1000 ROS 16/2000 Slide 27 Complex Modes - Modulation Time Spreading Avoid consecutive bit damage Minimises damage from impulse noise Heres an example: 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 26 Slide 28 Complex Modes Modulation - Interleaving 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 27 ABCDEF GHIJK MO L NPQR STUVWX YZ123 456789 0 4YSMGA Input by row Output by column Slide 29 Complex Modes Coding & Modulation Summary Two key points We add extra information (redundancy) to facilitate error correction We disperse the signal in time and frequency to minimise errors. 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 28 Slide 30 Complex Modes Mode Summary ModeBandwidthKeying Error Correction Mode ARQ/FEC FEC CodingPurpose AMTOR 170 FSK ARQ QSO PACTOR 200Hz FSK ARQ HF email QPSK31 31Hz QPSK FECConvolutionalQSO MFSK16 360Hz MFSK FECNASAQSO JT65A 200Hz MFSK FEC Reed- Solomonspecialist weak signal ALE 1750Hz MFSK FECGOLAYLink control ROS 500 or 2000Hz MFSK FECNASAQSO/ weak signal WINMOR 500 or 1600Hz MFSK bothNASAHF email V4Chat 200Hz MFSK bothNASAQSO Olivia 125 to 2000Hz MFSK FECWalshQSO/weak signal MT63 500 to 2000Hz MPSK FECWalshQSO/weak signal 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 29 Slide 31 Complex Modes Operation Get Going What do you need: PC with a sound card Windows XP (or later), Linux, Mac Software FLDIGI is good SSB transceiver and Antenna Two screened leads for audio in and out Optional interface unit 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 30 Slide 32 Data Modes Connections 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 31 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 Slide 33 Data Modes Operating Tips Listen first Use Hamspots Digital Section Use low power 5 watts is usually plenty Watch your modulation Keep to the band plans Use my sample messages Try conversing! 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 32 Slide 34 Questions Have a go its fun Any Questions? Dont forget to pick-up a handout 6th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 33