Ham Radio Paging - N5DUX

1 HamRadioPaging:Putting"POC5AG"onPacketWh ypaymonthlyfeesfornon-businesspagingserv iceswhenyourTNCcan dothejobforyou?ByPhilAnderson,WRJXI*The KPC-9612 TNC is the centerpieceofKantronics'packetpagingsyst em, with the latestreleaseofthe9612firmware. supporting the mode. Apersonalcomputermay also be used at any time,butyoucan'tkeepyourHTturnedonwhiley ou'reatwork. Oryou'retherepeatertrustee"oncall"incase anythinggoeswrong,butyourjobtakes youfromplaceto ,apagerwouldbejustthe thing to help you keepin touch. But apagingserviceisexpen-sive,especiallyif youwanttoequipawholegroup with ,ofcourse,you do your ham "WirelessWorld"conferencelastDecemberinS anFrancisco,I managedto take in theses-sions wascuriousabouttwo-waypagingand thefutureofpaging, , Icouldn'thelpthinkingaboutthesimilar-iti esbetweenpagingand9, (FSK)modulationand asynchronousdataformatwithcheckbits , Iobtaineda copyoftheInternationalRadioConsultativeC om-mittee's(CCIR) (R-584-1),morecommonlyknownas thePostOfficeCodeStandardizationAdvisory Group(POCSAG)code.

2 Iexaminedthatstan-dard,thoughtabouthow toimplementitinhardware,andoutlinedsomee xperi-ments to tryPOCSAG pagingon the andrunningtheexperiments,MichaelHuslig,K B0 NYK,KarlMed-calf,WK5M,and Isucceededinporting*PhilAnderson,W@XI,is thePresidentofKantronicsCo., Inc. Hecurrentlylivesin Lawrence, 1996thePOCSAG codeinto ourKantronicsKPC-9612 ,we hadproofofconcept:pag-ing frombenchtobenchusing a laptopcomputer,theTNCasPOCSAG encoder,a KenwoodTM-251 Awitha dummyload, andMotorolaBravoPlus"pagersrecrystalledt o ,twoexcitingamateurpagingapplicationscam eto alsoemerged:theTNCas apagingencodertotest/recrystalpagersand therealizationthatinexpensivepagerreceiv -ers can beconvertedforotheruses. Wehoped,too, thatpagingtechnologywouldaddsomemoreexci tementto our hobby,andwouldget a few folksbackinto tin-keringwiththeirsignalgeneratorsandos cilloscopesto"putthoseusedpagersonfreque ncy.

3 "CommercialPagingSystemsI'massumingyou'r efamiliarwith pag-ers but notwithhowcompletepagingsys-tems work. So,let'sexaminehow a typ-icalcommercialsystemis structuredandthenwe cancomparethat with our ,a localcontrolsystem(pagingterminal),sever alradiotransmitters,and arestrategicallyplacedHam Radio Above 50 MHzso that thesystem'soperatingarea is"covered"with an RF signal strongenough to reach each you purchase a pager from a pag-ing provider,they'llmake sure your pag-er'sreceiver is set for their Paging trans-mitter'sfrequency andthey'llassign anID (called acapcode)and phone numberto the pager. Then, when a page phonenumber is dialed, the page control systemmatches the phone number with the ID,prompts the caller for a message (whichthe caller enters using a Touch- Tone phone), and sends the page message tothe :FourTypes,FiveBandsPagers developed since 1978 are oneoffourtypes:tone, numeric, alphanumer-ic, or voice.

4 The vast majority sold todayare numeric. Most are also crystal-con-trolled, Whilesynthesizedpagers havebeen developed inrecentyears, crysta1-based pagers remain the favorite, perhapsbecause of price and battery life. Pagersare readily available for the VHF Low,VHF High, UHF, UHF High and 900-MHz bands and have been produced inthe millions (see Table1).The transmission format of the POC-SAG signal is similar to that of 9,600-baud packet Radio : frequency shift key-ing (FSK) modulation at devia-tion. That fact led us to realize that pag-ing could be adapted for use with ourKPC-9612 and "data ready" Radio equip-ment already at packet-like format of the digitalpaging code is a preamble of 576bits-alternating Is andOs-followedby oneor more batches ofmessagecodewords(see Table 2).

5 Each batch consists ofa32-bitsynchronizationcodeword(SC)fol- lowed by eight frames of 64 bits each,each frame consisting of two are defined assynchroniza-tion, idle, address, and formatfor the datacodeworddiffers slightlyfrom the rest, but all contain 10 check bitsHam Radio Above 50 MHzfor error detection and correction. A fulldescription of the POCSAG code can befound in CCIRR ecommendationR-584-1 or in thePagerHandbookforthe RadioAmateur(see References).Thetransmissionrate for POCSAG iseither 512, 1,200 or 2,400 baud. Theserates and the defined format of the codedetermine the shortest durations possiblefor a page transmission at a given various baud ratesappear in Table the commercial systems, an ama-teur system must consist of a Paging sig-nal encoder, atransmitter,and , of course, can be carried outby a PC or a TNC, and we chose to portour code into did thisfor several reasons: 1) because the TNCis easily located remotely; 2) because apacketconnection(for Paging ) can beeasilyaccommodated.

6 And 3) because,unliketypicalAFSK1,200-baudor9,6 00-baudG3 RUH-typepacketmo-dems, theintegratedcircuit modem in theKPC-9612'sport2 can accommodate thePOCSAG signalling make it as easy as possible for ama-teurs to experiment with packet Paging ,ourfirmwareupgrade version for theKPC-9612 includes the functions of dig-ital pagingtransmissionand monitoringof 512-, 1,200-, 2,400-baud numeric andalphanumericmessagesbasedon thePOCSAG standard. Pages are sent by en-tering an ID (capcode) and message for apager, using the PAGE command. For ex-ample, assumemypager' s capcode num-ber is 0111222 and your call-back num-beds555-1212,you'denter (at thecmd:prompt)PAGE 0111222 the Paging messagedoesn'thavetobe a phone be any stringof numbers, such as arepeaterfrequen-cy, so youcouldtypePAGE011222147060if you wanted me to contact youon firmware upgrade also includes apaging server (PS), similar to apacketmailbox, enabling Paging to"callsigns"with an entry in a page directory via aJuly 1996 TheRadioAmateur'sJournalVHF 7/9676 NorthBroadwayHicksville,NewYork11801 Pleasestartmy and rate(checkone): ~( ) Check ( )MIC()VISA ( ) AMEX()DiscoverCard NO.

7 !1 Expires_Signature_(SignatureRequiredon all charge orders)Please allow 6-8 weeks for delivery of first issue14 ,200 or 9,600 noted above, thePOCSAG standardcalls for a pagingtransmissionwith FSK at512-,1,200-,or 2, , atransmittercapableof handling audio with a frequency con-tent as low as 20 to 50 Hz is of the"9,600data ready" radiosmeet is the frequencycontentso low?The reason is two-fold: the FSK modu-lation and the absence of anybit-stuffingordata-scramblingdefined for the POC-SAG code. If a string of 1s is called forin the data, the carrier is shifted up by and held there. In addition, if a nu-meric page is sent that contains a largenumber ofOs(in a phone number such as842-1000, for example), then 15 "0" bitswill be sent in a row.

8 Thetransmittersim-ply must be able to handle these strings.(See the"DigitalDataLink"column inthe March and April,1996,issuesofCQVHF fordiscussionof9, )ReceivingYou have twochoicesforreceivingpages: use the TNC in monitor mode orrecrystala pager for yourclub' berecrystalledto another frequency, assum-ing they weremanufacturedfor the bandsegmentin which you wish to operate. Alisting of Bravo Plus receiver boards forVHFoperation(Table 4) is typical. The143~ are suitable fora crystal change to a frequency within 'vealsoconvertedsome from thehigherbandsegments,such club Paging system consists of aKenwood TM-251,aKPC-9612with ver-sion firmware, a batch of Bravo Pluspagersrecrystalledfor our local frequen-HamRadioAbove50 MHzcy, and adual-bandDiamondantenna ontheroofat 30 feet.

9 The system is housedin thecenterof a20, of 5 watts, we can activate pagersstored in a metal cabinet in the middleof the building. Plus, we can beep otheramateurslivingfive miles away. Ourlocalcommercialprovider, located fivemiles from us, uses a 100-watt transmit-ter with an antenna at 100 feet. Their sig-naleasilypenetratesour metal struc-ture-evento thecenterof thebuilding-andhas no trouble there you have it, a new mode toexperiment 'reinterested inemergencycommunicationsor remotecontrol of equipment, then digital pagingjustmight be for you. We can picture pag-ing messages reaching emergency work-ers via one, two, or even three nodes whenthe commercial phone and (hence) pag-ing systems are challenge now, it seems to us, isto take this technology and make use ofit alongside existing systems, particular-ly packet Radio .

10 By simply changing adaptor cups, theMasterChargerwilichargeanyYaesu,Motor ola, Icom, Kenwood, Alinco, 62 ON READER SERVICE CARDHam RadioAbove50 MHzElectricallyIdenticaltoMasterChargeri aIf. youhavetwodifferentradiosYOU'llonlyneed the switch to theleft or right, you candeterminewhichchargingcup INTHE FORFREECATALOGAND PRICE LISTJuly 1996