What’s All This RacketAbout Packet?

Packet radio is growing fasf. What’s it like? Read on.By Harold Price,* NK6K

This is an article about packet radio. If you don’t know speeds; 120 characters per second is standard on the 2-meter band,what packet radio is, that pronouncement won’t and a recent development permits ‘960 characters per second onmean much to you. “High Speed CD/CSMA Digital the 220-MHz band. Below 30 MHz, 30 characters per second is

Communications in the Amateur Radio Service, Theory and Ap,-plications” isn’t a real grabber either, so “this is an article about

used. Assuming that you already have a radio and a computeror terminal, it will cost you between $180 and $500 (higher cost

packet radio” will have to do. This article will have a slant for more “bells and whistles”) to get on packet radio. This isd i f ferent f rom mostprevious articles aboutpacket radio. It will notdiscuss what you will beable to do with packet inthe future, but what youcan do with packet now:how to use the existing net-works, which of severalfrequencies in your area arebeing used for packet,what packet controllers areavailable and what you canexpect when you get onpacket radio.

the cost of a terminal nodecontroller (TNC), a boxthat connects the data-generating device to theradio. In other words,packet allows hams to ex-change information muchfaster than before with noerrors at a reasonable cost.

What Is Packet?P a c k e t i s usually

character communication.Letters and numbersentered on a keyboard orfrom a computer are sentfrom one amateur stationto another. On the surface,this sounds no differentfrom RTTY, which hasbeen around in AmateurRadio for many years.Packet radio has threemajor characteristics andseveral beneficial side ef-fects that make it stand outfrom other amateur digitalcommunications modes.

After we discuss whatpacket does, there will besome theory-an explana-tion of how packet doeswhat it does (there’s nosuch thing as a free lunch).Those of you who want todig deep into technicaltopics should consult thebibliography at the end ofthis article.

A final word of warning:This is a sales pitch! Thegoal is to get you interestedenough in packet radio thatyou will get involved.Whether you visit afriend’s packet-equippedshack, see packet in action.at a radio store or Field

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lllllllllltllillllllllilllllllllilllllIlll~~~~i~l~~

Day site, go to localpacket-radio meetings, orjump in and buy or build a packet controller, you’ll learn farmore by doing than by reading.

Packet radio guaranteesperfect reception.

Information sent viapacket is checked to seethat it was received exactlyas it was transmitted. Datais automatically retransmit-ted until it is accurately re-

ceived. There is only a very small chance (one in millions) thatbad data will sneak through.

Executive SummaryPacket radio, or simply “packet,” is the common name for

a digital communications mode in Amateur Radio that provideserror-free communications. It is designed to allow automatic link-ing of systems for cross-country networks. Packet uses high

l 1211 Ford Ave., Redondo Beach, CA 90278

Packet permits a single frequency to be shared by severalsimultaneous conversations.

This also makes possible a bit of magic called a “simplexrepeater” -a repeater with its input on the same frequency asits output.

Packet allows for “routing” information among stations, so thatany packet station can be part of a linked set of “repeaters. ”

For example, there is a set of packet sta-tions in California that allows informationto be sent from San Diego to Sacramento,a distance of 480 miles, on 145.01 MHz.Before users of mega-linked VHF/UHFFM repeater systems start chuckling at this“paltry” distance, consider that each sta-tion on the packet link uses a single fre-quency, a single antenna and a singletransceiver. Stations do not require addi-tional telemetry, diplexers, duplexers, cir-culators, link radios or large amounts ofmoney. The packet-radio link can also sup-port multiple simultaneous conversationsbetween the ends of the path, as well asbetween points in the middle. Similarpacket-radio “networks” exist in Florida,the Northeast and Mid Atlantic states, andin several Midwestern states.

Like the man says on TV, “And whatwould you expect to pay for all this? Don’tanswer yet, there’s more . . .”

Packet allows computers to speak directlyto each other in their “native tongue.”

Most personal computers use the ASCIIcode, which has 256 separate characters.Baudot, the code most often associatedwith the term “RTTY,” has 32 charactersand a trick called “shifting,” which allowsan additional 26 characters to be recog-nized. Transmitting ASCII computercharacters over Baudot RTTY causesserious problems for computer users.Packet radio can transmit ASCII characterswith no restrictions or shifting.

Packet is fast.Packet is faster than Baudot RTTY

because of technical standards, equipmentavailability, convention and regulatoryissues. For whatever reason, you won’t seemuch Baudot above 100 words per minute(WPM). On the other hand, you won’t seemuch packet below 360 WPM on HF orbelow 1440 WPM on VHF. We are startingto see packet at 11,500 WPM on 220 MHzand above, and packet has been sent ex-perimentally at 300,000 WPM on the 7O-cmband. I’ve taken a small liberty in ex-pressing packet radio speeds in WPM; theactual speeds in bits per second (bit/s) are300, 1200,960O and 250,000, respectively.You say that you can’t type 300,000 wordsper minute, or even 360? Keep reading-packet isn’t just for typists.

Packet provides “non-realtime”communications.

What this means is that you and theperson you are talking to don’t have to behome at the same time. Much of the presentuse of packet radio is leaving messages forothers on a centrally located bulletin board.A bulletin board is a message-storagedevice, usually maintained at the home ofa local ham. If the person you want to talkto isn’t on the air when you are, you canleave a message for him or her on thebulletin board. The message can be about

plansanything: breakfasttomorrow, the fact that you worked theClipper-ton DXpedition on 160 meters, yournew antenna, etc. Although similar systemshave been available on traditional RTTYsystems, packet lends itself nicely tobulletin-board operation. Because packetis fast and many users can share the samechannel, a properly designed mailbox canshare the frequency with several non-mailbox conversations, or severalmailboxes can be on the frequency at thesame time without mutual interference.

Packet is information transfer.Because of these characteristics, packet

Iends itself well to connecting a central storeof information, usually called a hostsystem, to a local network of users. For ex-ample, in Southern California we have ahost run by WB6YMH that is kept stockedwith the latest Amateur Radio informationavailable. Electronic versions of the ARRL

Letter, Gateway (the ARRL packet-radionewsletter), the W5 YI Report, AMS’A TSateUite Report and newsletters fromseveral other organizations are madeavailable via packet radio and the hostsystem to any suitably equipped amateurin the area.* A typical issue of the ARRLLetter, around 20,000 characters, wouldtake about an hour to send at the standardRTTY speed of 60 WPM. At the standardVHF packet rate of 1200 bit/s, it takesabout 3 minutes.

Now, what would you pay for all of this?Wait, there’s more . . .

Packet i& 97.1(b).Part 97 of the FCC rules under which we

live states the purpose of the AmateurRadio Service. One of the subparagraphscontains these words: “Continuation andextension of the amateur’s proven abilityto contribute to the advancement of theradio art.” One of the better recent ex-amples of amateurs advancing the radio artis the current activity in packet radio.Packet didn’t originate in the AmateurRadio Service, but we have taken the basicidea and have shaped it into things thatdidn’t exist before, or which have a slantdifferent from what has been tried before.We have also added the traditional amateurtouch-extremely low cost. Amateur-designed and -built packet-radio controllersflew in official weather planes through theeye of a hurricane. Army and Navy MARSstations are integrating amateur packet-radio technology into their activities.Several commercial manufacturers havetaken the amateur-designed controllers andhave begun to sell them both in and out ofthe amateur market.

Packet is satellites.AMSAT-OSCAR 10 is an excellent

medium to use for packet radio. La,rgcamounts of data have been sent ,cross thecontinent via OSCAR 10. Using a specialpacket device called a teleport, a packet sta-tion in northern Canada was connectedthrough the satellite to a station in LosAngeles; data was then relayed throughanother packet controller to a station inSan Diego. The UoSAT-OSCAR 11satellite carries a packet-radio controllerthat can store 120,000 characters andretransmit them later to any other point onthe globe. PACSAT, an amateur satellitecurrently under development, will usepacket radio to store up to 4 millioncharacters for relay between stations.

Packet is international.The packet-radio protocol, AX.25, is

now accepted as an international standard.

‘Gateway, the ARRL packet-radio newsletter,is available from the ARRL. U.S. subscriptionsare $6 for ARRL members and $9 for non-members.

!: ‘8e&u& ik breaks’ up ai data stream into short secfions called frames, packet:T looks, to the oDerator, like full-dunlex communications+ FuH duDIex means both

2 puti& can speak at :..;‘;;rin& .yTk’i;, .:,(I’< y&L ,_ ?:, ;::“~$~ ’ ‘. , ;,; ., I

channel interference and other problemscommon in amateur communications.

***CONNECTED TO W6IXU

What Does It Look Like?So far we’ve talked about what packet

can do for you and about how it does it.But what does a packet contact look like?In the following examples, we’ll look at theprocedures used by the TAPR, AEA,Heath and Kantronics TNCs. Other TNCsfollow similar, but not identical,procedures.

First, you must tell the TNC your callsign. For example:

MYCALL NK6K

is the command to enter a call sign. MostTNCs allow you to change your call signat any time and have a way to rememberit while the power is off.

‘As in all other modes of Amateur Radio,packet allows you to “read the mail” ormonitor channel activity. This is called themonitor mode, and looks like this:

WA6JPR> WB6YMH: HELLO SKIP, WHEN ISTHE NEXT OSCAR 10 PASS?WB6YMH >WA6JPR: HANG ON WALLY, I’LLTAKE A LOOK.

The call signs of the stations involved ap-pear as “from> to, ” and the contents ofthe packet appear after the ‘2”. In thismanner, you can monitor all traffic on thefrequency. You can also watch for a sta-tion calling CQ, which might look like this:

WB6HHV >CQ: MIKE IN SAN DIEGOFOR ANYONE IN SIMI VALLEY.

LOOKING

You can send a CQ by entering the con-versation mode of the TNC. You go to theconversation mode by typing:

CONVERSE

You can then type your CQ:

MIKE IN SAN DIEGOIN SIMI VALLEY.

LOOKING FOR ANYONE

Your TNC adds your call as the FROM ad-dress, and CQ as the TO address. Thereceiving station’s TNC adds these ad-dresses to the front of the displayed text.

You answer a CQ or establish a contactby using the CONNECT command. This“connects” your TNC to another stationand begins the acknowledgment procedurediscussed earlier. An example of a connectcommand is

CONNECT W6IXU VIA WA60ZJ, K6TZ, WB6DAO

This asks for a connection between you andW6IXU routing through (via) three otherstations. When the connection has beenestablished, the TNC notifies you byprinting

This means that the computer in your TNChas exchanged some preliminary informa-tion with the other TNC and is ready toproceed. If the other station had alreadybeen in a connection with a third TNC, youwould get a busy signal:

***W6IXU BUSY

If W6IXU is not on the air, your TNCwould make several attempts to establishthe connection and then print a messagetelling you that it has not succeeded.

Assuming you get connected, everythingyou send to your TNC will now be sent toW6IXU with all the error checking andretransmission just described. Each timeyou hit the ENTER or RETURN key, a packetis formed and sent. Packets received fromthe other station are displayed between thelines you enter, much as if a full-duplexRTTY QSO were taking place.

When you are done with the con-versation, you disconnect by enteringCONTROL-C and typing DISC.

The commands and scenario above areall you need to know to carry on a packet-radio QSO. There are many other options(around 60) and several other combinationsof connected and monitor modes, but theyare like the 40 knobs, switches and meterson most modern HF rigs; there areoperators who constantly twiddle, andthose who only use the push-to-talk switchor the key.

So What Are You Waiting For?We’ve only touched briefly on what can

be done with packet and mentioned evenless the technical details of how it works.For some, packet is an end to itself-experimenting with new ways to transferdata. For others it is just a tool-anew wayto pass traffic, spot tornadoes, run aparade, score points on Field Day or meetnew people. To find out more, look intoany of the references listed at the end ofthis article. Or, wait for the second part ofthis article, which describes a TNC indetail. See you on packet!

BibliographyAX.25 Amateur Packet-Radio Link-Layer Protocol.

Newington: ARRL, 1984.First ARRL Amateur Radio Computer Networking

Conference. Newington: ARRL, 1981.Fourth ARRL Amateur Radio Computer Net-

working Conference. Newington: ARRL, 1985.Johnson, L., “Join the Packet Radio Revolution.”

73 Ma azine, Sept. and Oct. 1983, andJan. 1984

Morrison, Ml, and D. Morrison, “Amateur PacketRadio” Ham Radio, July and Aug. 1983.

Rinaldo, P., “ARRL Board Approves, A:$?&kW:;dio Link-Layer Protocol, I

Second ARRL Amateur Radio Computer Net-working Conference. Newington: ARRL, 1983.

Tannenbaum, A., Computer Networks. EnglewoodCliffs, NJ: Prentice-Hail, 1981.

Third ARRL Amateur Radio Computer Net-working Conference. Newington: ARRL, 1984.

The 1985 A RRL Handbook for the Radio Amateur,pp. 19-21 to 19-31. Newington: ARRL, 1984W