Digital CommunicationDigital Communication

How it started, what it is & we can do How it started, what it is & we can do with it today!with it today!

How It StartedHow It Started

1831 Insulated Wire1831 Insulated Wire 1836 Morse Code1836 Morse Code 1843 Fascimile1843 Fascimile 1870 Baudot Code1870 Baudot Code

Wires & SolenoidsWires & Solenoids

Current Loop SystemsCurrent Loop Systems Ranges in MilesRanges in Miles Easy RepeatersEasy Repeaters Multiple StationsMultiple Stations

Morse Code 1836Morse Code 1836

International Morse code composed of five elements:International Morse code composed of five elements: 1. short mark, dot - "dot duration" is one unit long1. short mark, dot - "dot duration" is one unit long 2. longer mark, dash is three units long2. longer mark, dash is three units long 3. inter-element gap within a character —one unit 3. inter-element gap within a character —one unit

longlong 4. short gap (between letters) — three units long4. short gap (between letters) — three units long 5. medium gap (between words) — seven units long 5. medium gap (between words) — seven units long Only non time sensitive digital schemeOnly non time sensitive digital scheme

Morse Code 1836Morse Code 1836

Manual Send, Paper Tape ReceiveManual Send, Paper Tape Receive First was soft paper & pin to crease tapeFirst was soft paper & pin to crease tape Operators learn to “hear” the code, tape is Operators learn to “hear” the code, tape is

abandonedabandoned (If you understand click and clack)(If you understand click and clack)

Morse Code 1836Morse Code 1836

Fax Machine 1843Fax Machine 1843

Write message in non-conductive ink on metal Write message in non-conductive ink on metal plateplate

Scan sheet with a needleScan sheet with a needle Remote solenoid makes inverse imageRemote solenoid makes inverse image Requires synchronized clockworksRequires synchronized clockworks

Baudot CodeBaudot Code 5 Element “byte”, two hand keyboard5 Element “byte”, two hand keyboard 2 & 3 Fingers, 30 WPM 2 & 3 Fingers, 30 WPM

Baudot CodeBaudot Code

Manual or punched tape on sendManual or punched tape on send Used punched paper tape on receiveUsed punched paper tape on receive Sender “clockworks” switches currentSender “clockworks” switches current Receiver steps tape, activates 5 solenoidsReceiver steps tape, activates 5 solenoids 5 bits means 32 symbols (letters)5 bits means 32 symbols (letters) Still used by TDD phone devicesStill used by TDD phone devices Still used by hams today for RTTYStill used by hams today for RTTY

Baudot CodeBaudot Code

Shift codes select alternate meaningsShift codes select alternate meanings

Digital Radio ModesDigital Radio Modes

There are 10 kinds of people in the world - There are 10 kinds of people in the world - those who understand binary and those who those who understand binary and those who don’t.don’t.

1980 FCC allows ASCII for hams1980 FCC allows ASCII for hams PC’s and sound cards make it practicalPC’s and sound cards make it practical Hams invent new modes – endlessly!Hams invent new modes – endlessly! JT-9 Announced last November – for 160MJT-9 Announced last November – for 160M

What is ASCII?What is ASCII? American Standard Code for Information American Standard Code for Information

InterchangeInterchange Originally a 7 bit codeOriginally a 7 bit code Later 6 bit (half ascii) and 8 bit (extended)Later 6 bit (half ascii) and 8 bit (extended) 6 bits means 64 values (no lower case)6 bits means 64 values (no lower case) 7 bits means 128 values7 bits means 128 values 8 bits allows 256 values8 bits allows 256 values Shift In, Shift Out, Escape extends further Shift In, Shift Out, Escape extends further

(DEC screen positioning codes)(DEC screen positioning codes)

What’s a Byte?What’s a Byte?

0 or 1, hi or low, 1270 / 1070 Hz, ???0 or 1, hi or low, 1270 / 1070 Hz, ??? 1 start bit1 start bit 6,7,or 8 data bits6,7,or 8 data bits 1 parity bit (Odd, even, or none)1 parity bit (Odd, even, or none) 1 stop bit1 stop bit Allows unsynchronized clocksAllows unsynchronized clocks Allows simple error checkingAllows simple error checking

Why All These Modes?Why All These Modes?

Radio is an analog mediumRadio is an analog medium Propagation is variablePropagation is variable Bandwidth is limitedBandwidth is limited Speed vs reliability Speed vs reliability Because we can!Because we can!

Basic PrinciplesBasic Principles Input data in binary form used to “modulate”Input data in binary form used to “modulate” Can change amplitude, frequency, phase Can change amplitude, frequency, phase Can use multiple tonesCan use multiple tones Mathematical functions used to generate an Mathematical functions used to generate an

analog signalanalog signal Same math functions used to recover data Same math functions used to recover data

from analog signalfrom analog signal Can include compression and error recoveryCan include compression and error recovery Everyone can invent a better function!Everyone can invent a better function!

The Big Modes – RTTY 1922The Big Modes – RTTY 1922

Usually 45 Baud, 170 Hz Signal, some 75 Usually 45 Baud, 170 Hz Signal, some 75 baudbaud

At 45 baud about 60 words per minuteAt 45 baud about 60 words per minute Surplus Teletype Model 26 in 1946Surplus Teletype Model 26 in 1946 FSK / AFSK audio frequency shift keying FSK / AFSK audio frequency shift keying PCs now function as “glass teletype”PCs now function as “glass teletype” Popular contest modePopular contest mode

The Big Modes – The ‘TOR’sThe Big Modes – The ‘TOR’s

SITOR - Simplex Telex Over Radio SITOR - Simplex Telex Over Radio AMTOR – Amateur SITOR (1970) 100 baudAMTOR – Amateur SITOR (1970) 100 baud PACTOR – AMTOR / Packet combo 200 PACTOR – AMTOR / Packet combo 200

baudbaud Data is sent in groups of 3 characters Data is sent in groups of 3 characters Receiver responds to each 3 character group Receiver responds to each 3 character group

ACK/NAKACK/NAK NAK causes retransmission of groupNAK causes retransmission of group Implies two station comms onlyImplies two station comms only

The Big Modes – PacketThe Big Modes – Packet

1200 bps AFSK TNCs used on 2-meters 1200 bps AFSK TNCs used on 2-meters AX.25 Protocol specifies channel access AX.25 Protocol specifies channel access

(ability to transmit on the channel) to be (ability to transmit on the channel) to be handled by CSMA (Carrier Sense Multiple handled by CSMA (Carrier Sense Multiple Access). Access).

Digipeaters retransmit if its call is in the Digipeaters retransmit if its call is in the digipeater field digipeater field

APRS is a packet systemAPRS is a packet system

The Big Modes – PSK31The Big Modes – PSK31

Developed by Peter Martinez G3PLX in 1995Developed by Peter Martinez G3PLX in 1995 Uses phase shift keying (BPSK or QPSK)Uses phase shift keying (BPSK or QPSK) Throughput is 31 baud, bandwidth is 31HzThroughput is 31 baud, bandwidth is 31Hz CW transmitter must put out 15 to 18 times CW transmitter must put out 15 to 18 times

more power than a PSK31 transmitter, to more power than a PSK31 transmitter, to achieve the same S/N ratio at the Rxachieve the same S/N ratio at the Rx

PSK31 more susceptible to frequency changes PSK31 more susceptible to frequency changes than CW or RTTYthan CW or RTTY but b but better under weak etter under weak signal conditionssignal conditions

The Big Modes – MT63The Big Modes – MT63

MT63 distributes the encoding of each MT63 distributes the encoding of each character over a long time period, and over character over a long time period, and over several tones. 100 WPMseveral tones. 100 WPM

64 tones 15.625Hz apart, in a 1kHz bandwidth64 tones 15.625Hz apart, in a 1kHz bandwidth Even if 25% of the character sent is Even if 25% of the character sent is

obliterated, it will give perfect copy obliterated, it will give perfect copy Wide bandwidth (1Khz for the standard Wide bandwidth (1Khz for the standard

method) makes this mode less desirable on method) makes this mode less desirable on crowded ham bands such as 20 meterscrowded ham bands such as 20 meters

Some lesser modes - CloverSome lesser modes - Clover

PSK mode which provides a full duplex PSK mode which provides a full duplex simulation simulation

Suited for HF operation (especially under good Suited for HF operation (especially under good conditions)conditions)

Clover’s key characteristics are band-width Clover’s key characteristics are band-width efficiency with high error-corrected data rates efficiency with high error-corrected data rates

Clover adapts to conditions by constantly Clover adapts to conditions by constantly monitoring the received signal monitoring the received signal

Hardware based mode and limited useHardware based mode and limited use

Some lesser modes - HellschreiberSome lesser modes - Hellschreiber

A method of sending and receiving text using facsimile A method of sending and receiving text using facsimile technology technology

This mode has been around a long time; the recent use of PC This mode has been around a long time; the recent use of PC sound cards as DSP units has increased the interest in sound cards as DSP units has increased the interest in Hellschreiber Hellschreiber

The single-tone version (Feld-Hell) is the method of choice for The single-tone version (Feld-Hell) is the method of choice for HF operation HF operation

35 WPM text rate, with a narrow bandwidth (about 75 Hz).35 WPM text rate, with a narrow bandwidth (about 75 Hz). Text characters are "painted" on the screen, as apposed to Text characters are "painted" on the screen, as apposed to

being decoded and printed being decoded and printed As a "fuzzy mode" it has the advantage of using the "human As a "fuzzy mode" it has the advantage of using the "human

processor" for error correction.processor" for error correction.

Some lesser modes – MFSK-16Some lesser modes – MFSK-16 An advancement to the THROB mode and encodes 16 tones An advancement to the THROB mode and encodes 16 tones Uses Fast Fourier Transform technology to decode the ASCII Uses Fast Fourier Transform technology to decode the ASCII

characters, and Constant Phase Frequency Shift Keying to characters, and Constant Phase Frequency Shift Keying to send the coded signal. send the coded signal.

Continuous Forward Error Correction (FEC) sends all data Continuous Forward Error Correction (FEC) sends all data twice with an interleaving technique to reduce errors from twice with an interleaving technique to reduce errors from impulse noise and static crashes impulse noise and static crashes

The relatively wide bandwidth (316 Hz) for this mode allows The relatively wide bandwidth (316 Hz) for this mode allows faster baud rates (typing is about 42 WPM) and greater faster baud rates (typing is about 42 WPM) and greater immunity to multi path phase shift immunity to multi path phase shift

Becoming a standard for reliable keyboard to keyboard Becoming a standard for reliable keyboard to keyboard operation and is available in several popular programs operation and is available in several popular programs

Some lesser modes – WSPRSome lesser modes – WSPR

For sending and receiving low-power transmissions For sending and receiving low-power transmissions to test propagation paths on the MF and HF bands to test propagation paths on the MF and HF bands

Can decode signals with S/N as low as -28 dB in a Can decode signals with S/N as low as -28 dB in a 2500 Hz bandwidth 2500 Hz bandwidth

Standard message: callsign + 4-digit locator + dBm Standard message: callsign + 4-digit locator + dBm (i.e. K1ABC FN20 37) (i.e. K1ABC FN20 37)

Duration of transmission: 110.6 secondsDuration of transmission: 110.6 seconds Transmissions nominally start one second into an Transmissions nominally start one second into an

even UTC minute: i.e., at hh:00:01 even UTC minute: i.e., at hh:00:01

NBEMSNBEMS

Narrow Band Emergency Messaging System Consists of four programs: Fldigi – Fast Light Digital modem application Flarq – Fast Light Automatic Repeat Request Flwrap – embed a checksum in a file Flmsg – easily send ICS forms and

Radiogram

NBEMS philosophy

Keep it cheap. Keep it simple. Use Open Source software. Don't depend upon infrastructure. Make it fun to use between drills and disasters. Any computer, any radio.

How NBEMS WorksHow NBEMS Works

Fldigi uses your computer's sound card to generate and decode digital signals.

All work is done by your computer, don't need an external Terminal Node Controller (TNC).

Audio from your computer speakers go into your radio's mike input for transmission.

Audio from your radio goes into your computer's mike or line-in for decoding.

Don't need an extremely powerful new computer, older machines work just fine.

Interfacing with computerInterfacing with computer

Rigblaster SignaLink But, if necessary, hold radio mike up to

computer speaker and... Hold radio speaker up to computer mike! In an emergency, don't really need hardwired

interface. Disable all DSP “enhancement” programs on

mic

Acoustic InterfaceAcoustic Interface Easiest way to interface radio to computer is to... Hold radio mike up to computer speakers. Hold radio speaker up to computer mike. You do PTT manually. Works especially well with VHF/UHF FM. Real gamesaver during emergencies. Allows you to easily send data using any radio. Hams can participate who do not have a soundcard interface. MT63 is sufficiently robust to deal with background noise,

even in a noisy EOC or field site.

Signalink USBSignalink USB

SignaLink ConfigurationSignaLink Configuration

SignaLink is very easy to configure. Just connect to computer via USB. Configure Fldigi to use SignaLink USB sound

card. Generate just enough audio from computer to

trigger SignaLink vox. Use volume controls on SignaLink and don't

touch computer audio settings

What Modes ?What Modes ?

Operating ModeOperating Mode MT63 – 2000MT63 – 2000 Olivia 16/500Olivia 16/500

If you have a decent FM voice channel start If you have a decent FM voice channel start with MT63-2000with MT63-2000

When MT63-2000 fails, switch to Olivia When MT63-2000 fails, switch to Olivia 16/50016/500

When Olivia fails, no communications.When Olivia fails, no communications.

ARRL RadiogramARRL Radiogram

Calculate Check

Today

Pick ARRL Message

ARRL Radiogram DeliveryARRL Radiogram Delivery

ICS 213 FormICS 213 Form

IC 213 HTML DeliveryIC 213 HTML Delivery

Where to find digital modes??Where to find digital modes??

6 Meter Band: 50.290 - 50.292 Mhz6 Meter Band: 50.290 - 50.292 Mhz 10 Meter Band: 28.110 - 28.125 Mhz10 Meter Band: 28.110 - 28.125 Mhz 12 Meter Band: 24.920 - 24.930 Mhz12 Meter Band: 24.920 - 24.930 Mhz 15 Meter Band: 21.060 - 21.090 Mhz15 Meter Band: 21.060 - 21.090 Mhz 17 Meter Band: 18.100 - 18.110 Mhz17 Meter Band: 18.100 - 18.110 Mhz 20 Meter Band: 14.065 - 14.090 Mhz20 Meter Band: 14.065 - 14.090 Mhz 30 Meter Band: 10.130 - 10.145 Mhz30 Meter Band: 10.130 - 10.145 Mhz 40 Meter Band: 7.060 - 7.080 Mhz40 Meter Band: 7.060 - 7.080 Mhz 80 Meter Band: 3.620 - 3.640 & 3.575 - 3.585 Mhz80 Meter Band: 3.620 - 3.640 & 3.575 - 3.585 Mhz

And What About D-Star?And What About D-Star?

All digital, all the timeAll digital, all the time Combined voice & data in 20 ms chunksCombined voice & data in 20 ms chunks Data stream about ½ voice, ½ dataData stream about ½ voice, ½ data Voice input is digitized, compressed, merged Voice input is digitized, compressed, merged

with data – calllsigns, repeater, routing, textwith data – calllsigns, repeater, routing, text GMSK modulation to create analog signal– GMSK modulation to create analog signal–

like cell phoneslike cell phones Limited forward error correctionLimited forward error correction

What does D-Star Add?What does D-Star Add?

Call Routing – repeater to repeaterCall Routing – repeater to repeater Reflectors – Hub for repeater “spokes”Reflectors – Hub for repeater “spokes” Allows simple text & small file exchangeAllows simple text & small file exchange Now HF as well as VHF / UHFNow HF as well as VHF / UHF

What Next?What Next?

Club event to set up PC’s and radiosClub event to set up PC’s and radios NBEMS net on W1SYENBEMS net on W1SYE Perhaps start a “Digital Team” of ElmersPerhaps start a “Digital Team” of Elmers Could we build a Rhode Island Net?Could we build a Rhode Island Net?