MOTOROLA GM 300 Information Page

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TheGM300wasMotorola'snextstepintheMaxTrac/Radiusmobileproductlines.Theschematicsare

remarkablysimilar.YoucaneveninterchangesomeboardsbetweentheGM300andMaxTracradios.

LiketheMaxTrac,theGM300linehasbeendiscontinuedbythemanufacturer.Throughoutthisarticle,

referencetoMaxTracradiosimpliesRadiusradiosaswell.

Naturally,youneeddifferentprogrammingsoftware(RSS),butifyou'veeverprogrammedaMaxTrac,

you'llberightathomewiththeGM300.Theradiosoperatethesame,too.Seebelowformoreinfoon

theRSSandprogramming.

GM300mobileradioscovertheVHF(136-174MHzintworanges)andUHF(403-520MHzinfour

ranges)bands,with8or16channels,12.5or20/25/30kHzchannelspacing,and10,25,and35-

45watt

powerlevels.Theyusethesameaccessories(loudspeakers,microphones,accessoryplugs,powercords,

mountingbrackets,etc.)astheMaxTracs.

TheM120radioisjustaboutthesameasaGM300buthas"lessfeatures"-thiswouldbethe2-channel

version,equivalenttoaMaxTrac50.

Here'safrontviewphotoofa16-channelMaxTrac,a16-channelGM300,anda2-channelMaxTrac:

MaxtracIndex

Motorolaindex

Homepage

Motorola GM300

Information Page

By Robert W. Meister WA1MIK

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Model Numbers:

ThefirstsixcharactersareprettymuchstandardMotorolaconvention.TheIFfrequencyisusually45.1

MHzbutifyouhavemultipleradiosneareachother,thiscancauseinterference,soyoucanoptionally

ordertheradiowithanalternateIFfrequency.

Thesecondsixcharactersprovidealotofusefulinformationaboutthecapabilitiesoftheradioandthe

boardscontainedwithinit.

Mount Power Band Series I.F.

M 0:01-10w 3:136-174MHz G M C:45.1MHz

 3:10-25w 4:403-520MHz   R:45.3MHz

 4:25-45w    

Spacing # Ch. Logic Board Range Rev.

0:12.5kHz 0:8 C:Expanded 1:136-162MHz A _

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AtypicalmodelnumberwouldbeM44GMC09C3A_.Thisisa40watt,UHFradio,45.1MHzIF,

narrowspacing(12.5kHz),16channels,expandedlogicboard,438-470MHzband.

Itisrarethatthemodelnumberincludesthespecificfrequencyrangetheradioiscapableofhandling

(10thcharacter).Youdon'tgetthatluckywithMaxTracs,Spectras,etc.Iwishallthemodelnumbering

wassouseful.

TheexpandedlogicboardhasitsfirmwarecontainedinasocketedEPROM,whichcanbereplaced.The

maskedlogicboardhasitsfirmwarepermanentlystoredinthesoldered-inmicroprocessorIC.Ihave

heardthatthemaskedlogicboardisonlycapableof8channelsmaximum.

ItwouldappearthatGM300sarenotcapableofanyformoftrunkingoperation.Howevertheycando

G-StarsignalingforusewithGEradiosystems.

Specifications:

Clickontheimagetoenlargeit.

2:20/25/30kHz 9:16 D:Masked 1:403-430MHz  

   2:146-174MHz  

   3:438-470MHz  

   4:465-490MHz  

   5:490-520MHz  

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NotethatarevisiontotheservicemanualshowstwoVHFranges:136-162MHzand146-174MHz.

Also,thepowerlevelsarecontinuouslyvariablethroughoutthethreeranges:1-10,10-25,25-45watts.

Board Numbers:

ThislistissortedalphabeticallybyFunction,thenDescription.

Board # Function Description

HLN8075A DisplayBoard 

HLN8070A LogicBoard Expanded,4-layer

HLN8070D LogicBoard Expanded,4-layer

HLN8047E LogicBoard Masked,2-layer

HLN8074A LogicBoard Masked,2-layer

HLE8385A UHFPowerAmp 403-433MHz,01-10Watts

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Logic Board Jumpers:

Clickontheimagetoenlargeit.

HLE8275A UHFPowerAmp 403-433MHz,25-45Watts

HLE8267A UHFPowerAmp 438-470MHz,01-10Watts

HLE8034A UHFPowerAmp 438-470MHz,10-25Watts

HLE8271A UHFPowerAmp 438-470MHz,25-40Watts

HLE8284A UHFPowerAmp 465-495MHz,25-40Watts

HLE8269A UHFPowerAmp 490-520MHz,25-35Watts

HLE8229A UHFRFBoard 403-433MHz,25kHz

HLE8230A UHFRFBoard 403-433MHz,12.5kHz

HLE8301A UHFRFBoard 438-470MHz,12.5kHz

HLE8300A UHFRFBoard 438-470MHz,25kHz

HLE8264A UHFRFBoard 465-490MHz,12.5kHz

HLE8263A UHFRFBoard 465-490MHz,25kHz

HLE8228A UHFRFBoard 490-520MHz,12.5kHz

HLE8227A UHFRFBoard 490-520MHz,25kHz

HLD8293A VHFPowerAmp 136-162MHz,10-25Watts

HLD8299A VHFPowerAmp 146-174MHz,01-10Watts

HLD8033A VHFPowerAmp 146-174MHz,10-25Watts

HLD8287A VHFPowerAmp 146-174MHz,25-45Watts

HLD8266A VHFRFBoard 136-162MHz,12.5kHz

HLD8265A VHFRFBoard 136-162MHz,25kHz

HLD8029A VHFRFBoard 146-174MHz,12.5kHz

HLD8031A VHFRFBoard 146-174MHz,25kHz

HLN8071A Vol/MicBoard 

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ThesearequitevisibleonthephotooftheGM300logicboardbelow.Notethatsomeofthesejumpers

arealsopresentonMaxTracsandhavethesamefunctions.

Accessory Connector:

Clickontheimagetoenlargeit.

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Notethatthe8-channelradiosignalsareslightlydifferentthanthe16-

channelradiosignals.Thatmaybe

duetothemaskedvs.expandedlogicboard.Fortunately,youcanuseanaccessoryplugwiredfora

MaxTrac(7-9,15-16)inaGM300.

Clickontheimagetoenlargeit.

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Theaccessoryconnectorandpinsarealsowell-documentedintheMaxTracsection.

Notethatmanyaccessorypinsontheexpanded(four-layer)logicboardareprogrammable,whereas

you'restuckwiththepinassignmentsonthemasked(two-layer)logicboard.

Channel Steering:

The16-channelexpandedlogicboardradiossupport"channelsteering"throughtheaccessory

connector.Youneedtoprogramthegeneral-purposeI/Opins(6,8,9,12,and14)for"ChannelSelect".

Theyturnintoabinarycodedinputthatallowsyoutoselectanyofthepossible16channelsby

groundingtheappropriateinputlines(assumingyou'veprogrammedtheradioforactive-lowinputs).To

selectchannel1,groundthe"ChannelSelect1"line.Channels1,2,4,8,or16maybeselectedby

groundingselectline1,2,3,4,or5respectively.Allotherchannelsareselectedbygroundingmultiple

selectlines.Ifyoureleasealloftheselines,theradiorevertstothechannelselectedbythefrontpanel.If

youselectachannelthatdoesnotexist(i.e.10channelsprogrammedandyouselectchannel16),the

radiorevertstothechannelselectedbythefrontpanel.ChannelsteeringDOESworkasexpectedon

radioswithmorethan16channels,i.e.youcanselectanythinguptochannel31,asthat'sallthat's

possiblewithfiveselectlines.

ThisdocumentdescribestheI/Oconnectorsettingsandshowsonewayofhandlingchannelsteering.

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Pins4,8,12,14canbeconfiguredforCOR.Pins6,8,9,12,14canbeconfiguredforChannelSelect.So

youcanputCORonpin4andCSontheothers.Thefactthatthemasked(8-channel)radiosandmost

MaxTracusersselectedpin8forPL&CORDetectissomethingthatwillhavetobechangedifyouwant

multiplefeaturesactivated.It'suptotheusertochoosethedesiredfunctionalitygiventhenumber(six)

ofprogrammableI/Olines.

Programming:

TheHVN8177programmingsoftware(RSS)programstheM10,M120,M130,andGM300mobiles,as

wellastheGR300,GR400,andGR500desktoprepeaters.ThelatestreleaseisHVN8177Fversion

R05.00.00datedDecember1995.TheRSSisshippedon3.5inchdiskettesandisaDOS-onlyprogram.

ThemicrophoneconnectorisexactlythesameasonaMaxTrac,andit'salsowell-documentedinthe

MaxTracsection.TheprogrammingcableandRIBsetupisthesameaswhatyou'duseforaMaxTracor

GTX.

Youcanhex-edittheMDFfileintheRSStoallowan8-channelradiototake16channels.Additional

informationisavailableelsewhereonthewebandfromColinLoweG1IVGhere.

TheGM300withtheexpandedlogicboardsupportsthesamecommonsignalingmodesasaMaxTrac

(PL,DPL,MDC,etc.).

Differences from a MaxTrac:

TheGM300hasmodelsthatfullycoverthe144-148MHzand440-450MHzamateurbands.Some

MaxTracswillgothatlowifyouadjusttheVCOandhex-edittheRSS.

TheGM300RFboardshavealocal/distantattenuatorinthereceiverfrontend.Thisreducesthegainof

thereceiverandimprovesintermodrejectionby10dB.YoucanputaGM300RFboardintoaMaxTrac,

buttherewillbenocontrolofthelocal/DXcircuit,andtheradiowillhavepoorsensitivity.Thecircuit

canbeactivatedbysolderingasmalljumperontheRFboard.TheGM300RSSandlogicboardsknow

howtocontrolthiscircuitry;theMaxTracRSSandlogicboardsdonot.

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TheGM300controlheadisquitesimilartotheMaxTrac.Thereisanadditionalcircuitboard,soldered

tothelogicboardpins,thatthecontrolheadconnectorspluginto,thatprovidessomeRFfilteringand

Zenerdiodestoprotectfromexcessivevoltage.Also,theinternalspeakernowconnectsthroughthe

controlheadcables,ratherthanonitsown2-wirecable.Thismakesiteasiertoremote-

mountaGM300.

Therearekitsavailableforthispurpose.

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Forcomparison,here'stheinsideviewofaMaxTrac.Noticethelackofshieldingandnofilterboard

betweenthelogicboardandcontrolhead.

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TheGM300logicboardissignificantlydifferentfromtheMaxTraclogicboard.ItcancontroltheRF

board'slocal/DXcircuit.TheaudiopoweramplifierisonesingleICratherthandiscretetransistors.The

heat-sinkisconsiderablydifferentandmountsonlytothebottomofthechassis-nomoreT8flat-head

screwsthroughthesideofthechassis.Therearefarfewercomponentsontheboardtoo.AllGM300

logicboardshavea16-pinaccessoryconnector.Afullmetalshieldcoverstheentirelogicboard,just

liketheyhavefortheRFboard;theMaxTraconlyshieldsthemicroprocessorarea.Thisfurtherreduces

spuriousemissions.

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

TheGM300audioamplifierdrivesbothsidesoftheloudspeaker.ThereforeyoumustNOTgroundeither

pin1orpin16oftheaccessoryconnector.Youmustruntwowirestoanexternalspeaker.Thesame

circuitdesignandcomponentsareusedontheSpectraradiosandtheysufferfromthesamerestriction.

Groundingeitherspeakerleadmayletoutthechip'slifetimesupplyofsmoke.

TheinternalloudspeakerfortheGM300(andMaxTrac/Radius)radiosisp/n5080085D03,howeverthis

partnumberhasbeenreplacedbyp/n5004639J01.Thisisa22ohm,5wattspeakerthatretailsfor

around$7USinearly2009.

TheGM300poweramplifierhasathermistormountednearthefinaltransistor,soitactuallysensesthe

heat-sinktemperature.Thelogicboardusesthistocontroltheoutputpowerinamorereasonableway;

thepowerwillbereducedif/whenthepoweramplifiergetshotenough,notwhenthemicroprocessor

"thinks"it'sgettinghotfromextendeduse.ThismakesGM300radiosmoresuitableforrepeater

transmitterusage.(Theystillneedadequateforced-aircooling.)Thisextrasignalrequiresa6-wirecable

andconnectorbetweenthePAandthelogicboard(theMaxTracsonlyhavea5-wirecableand

connector).IhaveheardthatyoucanuseaGM300PAinaMaxTracbysnippingthetemperaturesensor

wireofftheconnector,butIpersonallywouldnotbutchereithertheradioorthecablethatway.

Blanking the Radio:

Theredoesn'tseemtobealabversionofRSSfortheGM300.YoucanfoolRSSintothinkingtheradio

isblankbymanuallyerasingtheserialnumber(fillingitwithspaces)usingthebit-bangingfacility

availableintheMaxTraclabRSSprogram.Afterthat,youshouldbeabletoinitializetheradiousingthe

GM300RSS.Thatprocedureissimilarto,ifnotexactlythesameas,thestepsyou'ddoforaMaxTrac:

settheradiomodelnumber,frequencyrange,signalingfeatures,serialnumber,keyinthecrystaldata

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and9.6Vreading,andalignthepoweramplifieranddeviationcircuits.

Note:peoplehaveusedtheMaxTraclabRSStoblankGM300radios.TheytheninstallaMaxTrac

EPROM,makesomechangestothelogicboard,andturntheradiointoaMaxTrac,includingthemodel

number.ThentheyinitializeitwithMaxTracRSS.Thisprocedureisnotrecommended.

Toblanktheradio,youneedtodepositthefollowingdataatthelocationsshown.Thesevaluescame

directlyfromafactory-freshblankboard.Thisdatawillgodirectlyintotheradio'smemory.Youmay

wanttowritedownthecontentsoftheselocationsfirst,incasesomethinggoesterriblywrong.Ifound

thisinfoonthewebandhavenottrieditbecauseIdon'townaGM300.Useitatyourownrisk.All

valuesarehexadecimal.

Aftersettingthememorytothesevalues,theradiowillappearblankedtotheGM300RSS,andyou'll

havetogothroughtheblankboardreplacementprocedureandeitheraligntheradio,orfillinthe

variousfieldswithdatathatwaspreviouslythere.

Loc Data Usage

600 20 Serial#

601 20 Serial#

602 20 Serial#

603 20 Serial#

604 20 Serial#

605 20 Serial#

606 20 Serial#

607 20 Serial#

608 20 Serial#

609 20 Serial#

60A FF Panel#

60B FF Index#

60C 1B Index#

60D FF SWVer.

60E FF ???

60F 4F Checksum

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Bytheway,theRSSknowsaboutonlyone"panelnumber"fortheseradios:5,anditcoverstheRadius

GM300productandmodelsMxxGMC00D2xxandMxxGMC20D2xx.

TheabovetablevaluesaresupposedtoworkwithaGM300.ForanM120,changethevalueat60C

from1Bto20,andchangethevalueat60Ffrom4Fto54.

Common Problems:

Forsomereason,GM300sseemtobepronetolosingreceivesensitivity.Whetherthisisduetonearby

excessivetransmitterpoweroroperatorerror,theeventualcauseseemstobeeithershortedprotection

diodesacrossthereceiver'sinput,oradeadfirstRFamplifiertransistor.Allofthesecomponentsrequire

removaloftheRFboardtoaccessthem,butreplacementisquiteeasy.They'resurface-mount,ofcourse.

Theseradiosoftengowayofffrequency,tothepointthatthewarpadjustmentwillnotgetitbackwhere

itbelongs.Thecauseismostoftendirtyinterconnectionpinsinsidetheradio.ThesearebetweentheRF

boardandthelogicboard.OntheMaxTrac,theyareattachedtothelogicboard;ontheGM300thestrip

ofpinsismountedonthechassisandbothboardsplugintoit.Removebothboards,cleanthesepins,

andreinstalltheboards.Whiletheradioisapart,cleanthefrontpanelconnectorstoo.Thesesame

connectorsgetdirtyonMaxTracsaswell,butforsomereasontheydon'toftencauseseriousproblems

liketheydoontheGM300.

Toremovethelogicboard,youneedtoremoveaboutadozenscrews,includingalltheonesonthe

componentsmountedtotheheatsink.IfounditeasiertoremovetheRFboardfirst,thenfliptheradio

overandpullthelogicboardandtheinterconnectpinassemblytogether,thenremovetheinterconnect

fromthelogicboard.

Reference Oscillator Coarse Adjustment Procedure:

Ratherthantypethisparagraph,hereitisdirectlyfromtheservicemanual.Thissameprocedure(with

differentpartreferences)couldalsobeusedwithMaxTracradios.

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

Manuals and RSS:

-GM3008-channelOperator'sCard,6880902Z26

-GM30016-channelOperator'sCard,6880902Z41

-GM300Owner'sManual,6880902Z09

-GM300ServiceManual,6880902Z32



-GM300RSS,HVN8177F

-GM300RSSManual,6880902Z36

Acknowledgements and Credits:

DaveN1OFJsuppliedtheGM300andMaxTrac50radios.Thesephotosweretakenathisshack.

Allphotographsweretaken,andarecopyright,bytheauthor.

Muchoftheinformationforthisarticle,andthescannedpages,wereobtainedfromtheofficialMotorola

GM300ServiceManual.

AfewtidbitsofinformationweregatheredfromInternetsources.

GM300,MaxTrac,Radius,RSS,PL,DPL,MDC,andprobablyabunchofotherthings,aretrademarks

ofMotorola,Inc.

Contact:

Theauthorcanbecontactedat:his-callsign[at]comcast[dot]net.

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Thiswebpage,thiswebsite,theinformationpresentedinandonitspagesandinthesemodificationsandconversionsis

©

Copyrighted1995and(dateoflastupdate)byKevinCusterW3KKCandmultipleoriginatingauthors.AllRightsReserved,

includingthatofpaperandwebpublicationelsewhere.

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