Table Of Content

Copyright©2008 by TheAmericanRadio RelayLeague CopyrightsecuredunderthePan-AmericanConvention II1~ternationalCopyrightsecured This workispublicationNo.332ofthe RadioAmateur's Library,publishedbythe League.Allrights reserved.No ./ partofthiswork maybereproduced inanyform except withwritten permissionofthepublisher.Allrights of translationarereserved. PrintedinUSA -Quedanreservadostodoslosderechos ISBN: 0-87259-122-0 FirstEdition SecondPrinting Foreword Acknowledgements Chapter 1 • Packet Radio Fundamentals Chapter 2 • The Automatic Position Reporting System Chapter 3 • Packet and Public Service Chapter 4 • D-STAR Chapter 5 • Digital Meteor Scatter and Moonbounce with WSJT . .Chapter 6 • APCO-25 Chapter 7 • High Speed Multimedia (HSMM) Radio Appendix A • AX.25 Link Access Protocol for Amateur Packet Radio Appendix B • D-STAR System (Technical Description) Appendix C • APCO-25: Anatomy Of The Common Air Interface Index When the Internetbecamepart ofeveryday life, the amateurpacket radio networks that had flourished in the 1980s and early '90s declined sharply. Tosome,the collapse ofpacket spelled the end of digital AmateurRadio above 50 MHz.How wrong they were! Although packetnetworks see less activity than they did decades ago, packet radio itself is far from dead. Packetradio has been "repurposed" to createthe popularAutomatic Position Reporting System, and traditional packet networks still exist to supportpublic service activi ties. New software applications have greatly enhancedtheir function. Thanks to pioneering work by Joe Taylor,KUT, hams cannow enjoy digital meteorscatter contacts and even moonbounce on VHF and UHFfrequencies with modeststations. His WSJT software is available free of charge and requires little more than an ordinary computer sound device. TheJapan AmateurRadio League developed the D-STARdigital voice and data standard, and ithas seen significantgrowth in the United States as hams establish D-STAR repeater networks on VHF, UHFand microwave bands. Amateurs are even experimenting with the APCO-25 standardused bypublic service agencies. They'rereprogramming commercial APCO-25 transceivers for use on 2 meters and 70cm. All ofthese topics, and more, are discussed in this edition ofthe ARRL VHFDigital Handbook. My hope is that you'll use this booknot only as a helpful reference, but also as an inspiration to try your own VHF+ digital experimentation. David Sumner, KIZZ Executive Vice President Newington, Connecticut January 2008 Theauthor wishes to thankthe following individuals and organizations, whose contributions helpedmake this book a reference that many readers will enjoy. • Allan Crosswell, N2YGK and Bill Covey,WIGTT, for theircontributions to Chapter2. • Rick Muething, KN6KB,AlanIsaachsen, KB2WF and Jim Oberhofer, KN6PE, for materials used in Chapter3. • Ray Novak, N9JA,ofICOM Americaand Ward Silver,N0AX,fortheir contributions to Chapter4. • Joe Taylor,KIJT, for his WSJT UsersGuide andReference Manual, portions of which appearin Chapter5. • Pete Lunness,AScT,Training and SpecialProjects,Daniels Electronics Ltd, for the use of Chapter4:Anatomy OfThe Common AirInterface from the Daniels Electronics APCO-25 training manual,which has beenreprinted in Appendix C. • T.J.Molenkamp, KC8LTS,for his contributions to Chapter6. • John Champa, K80CL,for authoring Chapter7. l' -, acket radio is not a new phenomenon. Nor is it octets (2 and 10call signs) and consists of a destination, - confined to Amateur Radio, or to VHF, for that source and up to 8 intermediate repeating stations. The , matter. address is 7 octets consisting of the call sign followedby Inthebeginning,there wasX.25,aprotocolforwide the 4-bit (SSID) and 4 flag bits. Flag bits ofnote include area digital networks that typically communicated over the repeatedand end oflist (last repeating station) mark telephonelines.Withoutgoingintogorydetail,X.25works ers. by chopping data into strictly definedpackets, orframes Control-ThisisusedmostlyforAX,25 connection of information. This is accomplished by a device known oriented protocol. as a PacketAssembler/Dissembleror PAD. Each packet PID - The protocol ID identifies what higher-level issenttothedestinationdevicewhereanotherPADchecks protocol the frame carriesdata for.Examplesinclude: it for errors. Iferrors are discovered, the packet must be • AX.25 layer3(virtualcircuits - connections) sent again.This ensures that the datathe user receives is .InternetProtocol(IP frames inside UI frames) 100%errorfree. .AddressResolution Protocol (call sign-to-IP address) In the early 1980s,amateurs began adaptingX.25 for .Nolayer3(UI frames) over-the-airdigitalcommunications. TheresultwasAX.25. The new AX.25 protocol worked in much the same way, Information- Thisisthe "text" ofthe message. although itidentifiedeach messagebysenderanddestina FCS - A checksum used to detect garbled tion station call signs and added a Secondary Station ID packets so they can be ignored. number (SSID) in a range from 0 through 15.The entire Instead of a PAD to create and decode these AX.25 AX.25 protocol descriptionisincluded as an appendix to packets, hams invented the Terminal Node Controller;or this book. TNC. Unlike PADs, TNCs do much more than assemble As withX.25,each AX.25 framehas adefinedstruc and disassemble data. A TNC is programmed to work tureasshowninFigure1-1.Theframeislogicallybroken withinaradionetworkwheretheremaybeothercompeting upinto the following fields: signals. For example, to maximize the throughput for Flag- Theflag is adelimiterbetween frames. The everyone on the same frequency, a TNC is designed to 01111110 pattern is unique due to bit-stuffing (any time detect the presence ofother data signals.Ifithas apacket five Isare seen,azeroisstuffedandvice-versafordecod to send, but detects a signal on the frequency,it will wait ing).Extraflags arepermittedbetweenframes. This gives untilthefrequencyisclear.TNCsalsohaveavarietyofuser receiver time to sync up to the received signal and also adjustments and other features, such as mailbox functions allows the transmittertorun continuously ifithas to. that allow them to store messages when the operators are Addresslist- The address listisbetween14and70 away. Packet Radio Fundamentals • I-I ARRL0150 r----.--------,---,--------,---.----,--------.------r~:_:_:_:_::T:":~::T~:_::::I Flag Flag Flag Address Gtrl PID Information FGS Flag Flag Flag Figure 1-1-TheAX.25packet frame structure(seetext). The First TNCs and the with the demand. Soon after, several US manufacturers Packet Revolution began producing their own TNCs based on ,the TAPR TNC-2standard.Infact,theTNC-2becamethe standard InMarch1980theFederalCommunicationsCommis for packet radio world wide. sionapproved the use oftheAmerican StandardCodefor The packet fever spread quickly. For the first time, Information Interchange, or ASCII, for Amateur Radio. hams discovered that they could use ordinary VHF FM Prior to 1980, hams had been restricted to the limited transceivers to create over-the-air data networks. These Baudotcodefamiliartoradioteletypeenthusiasts.Baudot networks began springing up around the country, most can communicate the English alphabet, the number 0 centered on collections of stations that functioned as to 9 and some punctuation. ASCII, in contrast, contains Packet Bulletin Board Systems, or PBBSs. Hams could 128letters, numerals,symbolsand specialcodes,each of connect to PBBSs directly, or through relaying stations, which is represented by a unique binary number. Every and read or send Amateur Radio e-mail. Some PBBSs keyboardcharacterisrepresented inthis set.WithASCII, offered small filedownloads,too.Itwasevenpossibleto hams finally had access to what was then the standard configure your TNC mailbox function to automatically languageforcomputer-to-computercommunication. respond to queries from the PBBS and transfer e-mail The FCC approval came 18months after Canadian without you ever lifting afinger. "- hams hadbeenauthorizedtotransmitASCIIandtheyhad Most user activity was conducted at a signaling rate already been working on a protocol for doing so.Tothat of 1200 baud, although there were PBBSs that accepted end, Doug Lockhart, VE7APU, of Vancouver, British 9600 baud connections.On the HF bands,hams are lim Columbia,developedthefirstTNC. It worked withamo itedto300baud,butthatdidn'tstopamateursfrom setting demtoconvertASCIItomodulatedtonesand convertthe up HF links torelayinformation'betweenscattered pack demodulated tonesbacktoASCII. Doughad alsoformed et networks throughout the nation and, eventually, the the Vancouver Amateur Digital Communications Group world. (Beware of confusing baud with bits per second. (VADCG) and namedhisTNCthe "VADCG board". See the sidebar "BaudvsBPS vsThroughput.") Hams in the US started experimenting with the VADCG board, but in December 1980Hank Magnuski, KA6M,put adigital repeateron2meters using aTNCof hisowndesign.Agroupofhams interestedinHank'sTNC started working together on further developments in packet radio and formed thePacificPacket RadioSociety (PPRS).At the sametime,AMRAD,the Amateur Radio Research and Development Corporation,in Washington, DC became the center forpacketwork on the eastcoast. In 1981 a group of hams in Tucson, Arizona, founded the Tucson Amateur Packet Radio Corporation . (TAPR).With three centers of amateur packet re search in the US, itwasn't long before one group would take the lead:TAPR. TAPR pioneered the TNC-1, first commerJ cially successfulpacketTNCin the United States.By 1984theyintroduceditssucces sor, the TNC-2. The TNC-2 design was much more compact, easy to use and highly reliable. The TNC-2 was enthusi astically received by the mushrooming If. amateur packet community, so much so •'7 that TAPR had difficulty keeping pace TheTAPRTNC-2. 1-2 • Chapter I Then Came the Internet quicklybecamethestandardfortextcommunication with millions (and eventually billions) of people exchanging TheInternet hadexistedforyears andwaswellknown messages every day. What was once esoteric was now ingovernment, militaryandacademiccircles.Itsexposure commonplace. to the general public in the late 1980s coincided with the TheeffectoftheInternetonpacketradiowasdevastat increasing popularity of personal computers. Ordinary ing. Unlike amateur packet radio, the Internet was ex citizens began tapping the Internet through connections tremely fast, reliable over long distances and capable of providedbytheiremployers,orbycollegesanduniversities. easily handlinglargefiletransfers.Theallureof"instant" The revolutionary potential of the Internet was obvious, global e-mail wastoogreatformost packet users toresist. butunless youknew your wayaroundthecrypticTCP/IP Theyabandonedtraditionalpacketradioin droves,which language, using the Internetcould be achallenge.Some resultedin the shrinkageorcollapseofamateurnetworks thing more wasneededbefore theInternetcouldspreadto throughouttheworld.The effect wassimilartotheimpact an even larger audience. "Somethingmore" arrivedin 1991.Thatwasthe year cellular telephones had on amateur repeater autopatch theConseilEuropeenpourlaRechercheNucleaire(CERN) systems. Once everyone had an affordable and private established their newWorld Wide Web projectwith Web wirelesstelephone,the practice of making a call through "pages"createdinHypertextMarkupLanguage,orHTML. an autopatch wasrenderedobsolete. In 1993the National CenterforSupercomputingApplica This is not to by that amateur packet radio is dead. tionsatthe University ofIllinoisreleasedMosaic,thefirst There are many packetnetworks still in place. What has Webbrowser.Finally,thepublichadanextremely"friend happenedinsteadisthat packetradio hasbecomespecial ly"toolfornavigatingincyberspace.TheWeb,asweknow izedthroughapplicationsdesignedtomeet specificneeds. ittoday, wasborn. We'll discusstheseapplicationslaterinthebook.The most Therest,asthey say,ishistory.TheWebexplodedin popular application of Ax'25 packet radio today is the popularity andwithin5yearsbecamemainstreamtechnol AutomaticPosition Reporting System, or APRS,and that ogy,asfamiliar asahousehold telephone. Internete-mail subject hasachapterall itsown. v., Baudvs BPSvsThroughput These threetermsareoftenconfusedandmany creates a 1200baud outputsignal.Thankstoclever hamsusethem interchangeably. By definition,however, coding,themodem iscapableofencodingtwobitsfor theyarequitedifferent. every signalchange,so it isoperating at2400 bps The baudrateisameasureof how many times per (1200 baud x 2).Sofar sogood,butlet'ssaythe radio secqnd a signalchanges states (from "mark"to "space" issendingthe2400 bps data on a path that isproneto inG.lra.dioteletypet~ansmission, for example)inone [email protected]!ectserrors ' . heterm aud"comesfrom EmileBaudot, G.lr1dframeshG.lY'Eltobe re-V . 'ttedm or oft nchronoustelegraph printer. thoughthe sen(jingstation'i .. ingd BRS-"-Bitspe econd-is afneasure of how many bps,thethroughput,based 0 .he amou ....... <> a bitsper secondaretransmitted.Withsome digital successfully decoded atthe receiving statton;ismuch codingschemes,itispossibletoencode multiplebits lower. - -- per baud resultinq inbit ratesthatexceedthe baud rate. Bewarywhenyou readmanufacturerclaims about Throughputisa measureofthe amountofdata equipmentthat cantransferdata atspecific ratesover transferredinaspecificamountoftime,usually radiochannels.Dothey meanthe encodedbits per expressed inbitsper second (bps).Thisis acritical secondatthetransmitter,orthe effective throughput? distinctionbecause throughputcan be independent of Inmost instances,theymean.thedata ratea.tJhe baudrateorencoded bitspersecond. transmitter.When youtaketheirhardwareintc,thereal. AILthreetermsqan cometogetherinsome World,your tivethrou ' b . . , intElr~$ting ways. Imagineyouhavea.radlo modemthat >dIfferent. - Packet Radio Fundamentals • 1-)