Remote squelch detect for use with a radio receiver
Contents
1. 3 1323 y TTQVNG 1 J _ o 1 EON SNISYVHO 13534 1 1055 39 LINN JINON ANVONO23S INGON 06 SW31SAS 900 HOIVM U S Patent May 31 1988 Sheet 3of16 4 748 685 21 FIG 6 U S Patent May 31 1988 Sheet 4 of 16 4 748 685 FROM SECONDARY MOBILE UNIT E TRICKLE DATA RESET 302 CHARGING UNIT 801 799 MPO DATA RESET _ m WATCH DOG e PORTABLE UNIT ALARM 4 gt MICROPROCESSOR 23 109 VOICE MA q RECEMER ee L x24 4 MOIVTII2SO 01 111250 1 201 1 201 021 0235 15814 4 748 685 S9NISS3903d 5 n M31INT1 3311N4 9 155320 4 olan 39 un 55 3 VIVO 2 27 VA LJ en gt IN3WISrIPGV NOLLVIA3Q 601 U S Patent 4 748 685 Sheet 6 of 16 U S Patent May 31 1988 4 748 685 Sheet 7 of 16 May 31 1988 U S Patent 6 OIA 31891304 WOMJ 0H23 181 101 ale Tg 2 LA 922 T L LEZ siz SEZ 212 812 602 622 oz 02 erz E eue SN 225 912 4 748 685 Sheet 8 of 16 31 19882. missed message signal functions In order to comple ment these secondary mobile unit 51 functions the portable unit microprocessor 801 requires additional programming as well With reference to FIG 20 the portable unit microprocessor 801 can begin by deter mining whether a range burst transmission from the secondary mobile unit 51 has been detected 921 If not a count 1 can be incremented 922 and a determi nation made as to whether this count 1 exceeds a prede termined threshold Z 923 If count 1 does not exceed this threshold the microprocessor 801 can move to an out of range flag set determination as explained below If count 1 does exceed this threshold 923 however an out of range flag can be set 924 and the subroutine can continue If a range burst has been detected 921 the out of range flag can be cleared 926 as can count 1 927 Following the above determinations and actions the microprocesor 801 next determines whether the out of range flag has been set 928 If it has been set the microprocessor 801 provides an appropriate alarm 929 through appropriate sounding of an alarm unit 799 FIG 8 provided for that purpose Following the above actions the microprocessor 801 can determine whether any missed message sig nals have been received from the secondary mobile unit 51 931 If not the microprocessor 801 can return 932 If a missed message signal has been detected 931 how
3. signal detect means for detecting presence of said test signal subsequent to passage of said signal through said squelch means such that said signal detect means will provide a squelch detected signal whenever said switch means connects said squelch means to said audio signal source means and said squelch gate is open ks
4. unit 51 from time to time One embodiment of the invention lets the operator known when the portable unit 10 has moved out of range of the secondary mo bile unit 51 and also when the secondary mobile unit 51 has transmitted a message that the portable unit 10 has not received With reference to FIG 19 the secondary mobile unit microprocessor 701 can be programmed to operate to provide both a range burst and a missed message signal when appropriate For example the secondary mobile unit microprocessor 701 can increment a count 1 901 and then determine whether this count 1 exceeds a predetermined threshold 902 If not the micro processor 701 can proceed to the next inquiry If count 1 does exceed this variable however the secondary mobile unit 51 can transmit a range burst signal 903 and then clear count 1 904 In this way the secondary mobile unit 51 will from time to time transmit a range burst signal to the portable unit 10 which the portable unit 10 can use to confirm within range status Typi cally the range burst signal can be comprised of a sub audible digitized code that can be created by the sec ondary mobile unit 51 and imparted to the portable unit 10 at the same time that the IDs PTT and emer gency codes are created and imparted as described above Following the range burst process the microproces sor 701 determines whether a message flag has been 4 748 685 17
5. 206 coupled by a 91 picofarad capacitor 207 A voltage divider comprised of a 68 k ohm resis tor 208 and a grounded 120 ohm resistor 209 con nects to the base of an M9494 transistor 211 the emit ter of which connects to a parallel grounded 27 k ohm resistor 212 and a 390 picofarad capacitor 213 The collector of this transistor 211 connects to a parallel configured variable inductor 214 and 9 pico farad capacitor 216 and also connects through a 2 picofarad coupling capacitor 217 to a grounded induc tor 218 and a serially connected 13 picofarad capacitor 219 and 70 picofarad capacitor 221 The common node between the latter two capacitors 219 and 221 connects to a voltage divider comprised of a 6 8 k ohm resistor 222 and a 6 2 k ohm resistor 223 and also to the base of an M9494 transistor 224 the emitter of which connects to a parallel grounded 100 ohm resistor 226 and 390 picofarad capacitor 227 The collector of this transistor 224 connects to a choke 228 and through a 16 picofarad coupling capac itor 229 to a grounded 17 picofarad capacitor 231 and also to a voltage divider comprised of a 6 8 k ohm resistor 232 and a 6 2 k ohm resistor 233 The com mon node between these resistors 232 and 233 con nects to the base of a third M9494 transistor 234 the 0 30 40 60 65 8 emitter of which connects to a parallel grounded 510 ohm resistor 236 and 470 picofarad
6. 707 The speaker terminals 710 can be monitored to determine the presence or absence of the audio signal In particular each terminal can be connected through a 0 1 microfarad capacitor 716 and 717 to the inputs of a first operational amplifier 718 In addition the in verting input of the operational amplifier 718 can be connected to a 330 k ohm resistor 719 that connects to a positive 5 volt source and to the noninverting input thereof through a 10 k ohm resistor 721 The nonin verting input of the operational amplifier 718 can also be connected to a grounded 150 k ohm resistor 722 Finally a 0 001 microfarad capacitor 723 can be con nected between the two inputs to the operational ampli fier 718 and a second 0 001 microfarad capacitor 724 can be connected between the noninverting input and ground The output of this operational amplifier 718 con nects through a diode 726 to the noninverting input of a second operational amplifier 727 which input also connects to a grounded parallel configured 82 k ohm resistor 728 and 0 15 microfarad capacitor 729 The inverting input of this second operational amplifier 727 connects to a reference voltage VREF having a value for instance of 1 8 volts So configured the output 731 of the second opera tional amplifier 727 comprises a transmit enable port that can be utilized by the secondary mobile unit trans mitter to enable transmission of the audio si
7. FIG 13 comprises a schematic diagram of interface switches for use in the secondary mobile unit FIG 14 comprises a schematic diagram of a watch dog circuit FIG 15 comprises a schematic diagram of the battery charging and interface circuit FIGS 16 a and 16 0 comprise a flow chart of the new code generation and transfer process FIG 17 comprises a flow chart of portable unit oper ation under certain operating circumstances FIG 18 comprises a flow chart of secondary mobile unit operation under certain operating circumstances and FIG 19 comprises a flow chart of portable unit oper ation under certain operating circumstances BEST MODE FOR CARRYING OUT THE INVENTION Referring now to the drawings and in particular to FIG 2 the invention can be seen to comprise a portable unit transmitter 10 or transceiver as the case may be and as explained in more detail below that communi 55 cates with a secondary mobile unit 51 that mounts in a vehicle 12 The secondary mobile unit 51 connects to a primary mobile unit 11 that in turn communicates with a base station 13 In effect the primary and sec ondary mobile units 11 and 51 function as a repeater to connect the portable unit 10 to the base station 13 In an application where the portable unit 10 in cludes only a transmitter and effectively comprises a cordless microphone the portable unit 10 must meet certain FCC requirements governing operati
8. back diodes 496 and 497 to the inverting input thereof and to a series connected 100 k ohm resistor 498 and 0 68 microfarad capacitor 499 The output of the second LM324 494 comprises the data output port 136 that may be appro priately connected to a relevant microprocessor either in the secondary mobile unit 51 or the portable unit 10 to allow decoding of the data signals So config ured the second LM324 494 in the data processing channel 133 serves as a limiter and the first LM324 489 serves as a low pass filter Referring now to FIG 14 the secondary mobile unit microprocessor 801 can have one output connected to a switch 1601 comprised of a 10K ohm resistor 601 and a 9642 transistor 602 This transistor 602 can have a grounded emitter and a collector that connects to the emergency activation switch as found for in stance in a Systems 90 module 52 So configured the secondary mobile unit microprocessor 801 can trigger the emergency transmission function of the Systems 90 module 52 Another switch 1602 comprised of a similar resistor and transistor can be provided in addi tion to a 1 k ohm collector resistor 603 to allow the microprocessor 801 to control the primary mobile unit s push to talk function and thereby allow a push to talk ID to be transmitted by the primary mobile unit 11 and for audio as received by the secondary mobile unit 51 to be transmitted by the primary mobile uni
9. capacitor 237 The collector of this transistor 234 connects to an inductor 238 and also to a filter stage 108 The filter stage 108 includes two grounded capacitors 239 and 241 that are joined by an inductor 242 and through a coupling 22 picofarad capacitor 243 to an appropriate antenna 109 In a system where the secondary mobile unit 51 and the portable unit 10 both comprise complete transceiv ers some means must be provided for allowing the secondary mobile unit transmitter to have its transmit mode enabled voice responsive mechanism could be utilized to enable the secondary mobile unit transmitter whenever the output of the primary mobile unit 11 indicates the presence of an audible signal These mech anisms however are typically slow to respond and often result in lost information Another approach would be to directly access the squelch detect of the primary mobile unit 11 and connect appropriate wires to it to allow the squelch detect of the primary mobile unit 11 to control the transmit enable function of the secondary mobile unit transmitter Although this would accomplish the necessary function this approach repre sents substantial cost from the standpoint of retrofitting such a system into an existing mobile radio installation In one embodiment of this invention a transmit en able signal for the secondary mobile unit transmitter can be provided through appropriate monitoring of the primary mo
10. ground and the base of which connects to a 5 k ohm resistor 478 to receive a squelch signal from the sec ondary mobile unit microprocessor 701 The collector of this transistor 477 also connects through a 6 8 k ohm resistor 479 to the output of the LM324 474 which also directly feeds back to the inverting input thereof The output of the LM324 474 connects through a 10 microfarad capacitor 481 to a voltage divider comprised of a 4 7 k ohm resistor 482 and a 13 k ohm resistor 483 that is biased between a positive 5 volt source and ground The voltage divider in turn connects to the base of a 9642 transistor 484 the emitter of which connects to a grounded 1 5 k ohm resistor 486 and the collector of which connects to the microphone high input line of the primary mobile unit 51 in the vehicle The data processing path 133 receives its input through a 360 k ohm resistor 487 which in turn con nects through a 120 k ohm resistor 488 to the nonin verting input of an LM324 489 and through a 0 012 microfarad capacitor 491 to the inverting input thereof The noninverting input also connects to a 20 35 40 45 12 grounded 0 0018 microfarad capacitor 492 and the inverting input connects to the output thereof In addi tion the output connects through a 30 k ohm resistor 493 to the noninverting input of a second LM324 494 with the noninverting input also connecting through parallel connected back to
11. processing means for rendering at least a por tion of said demodulated signal audible when said squelch gate is open the remote squelch detect comprising A audio signal source means for providing an audio signal B switch means for selectively connecting said squelch means to said discriminator means output and to said audio signal source means and C signal detect means for detecting the presence of said audio signal at the output of said signal pro cessing means such that said signal detect means will provide a squelch indication signal whenever said switch means connects said audio signal source means to said squelch means and said squelch gate is opened 2 The remote squelch detect of claim 1 wherein said signal detect means includes comparison means for comparing said detected audio signal with a reference signal to thereby determine presence and absence of said audio signal 3 A remote squelch detect and transmitter enable device for use with a receiver and a transmitter wherein said receiver includes discriminator means for demodulating an incoming signal and for providing at an output thereof a demodulated signal squelch means for responding to said demodulated signal by closing a squelch gate in the presence of a viable demodulated signal and by opening said squelch gate in the absence of a viable demodulated signal and said transmitter includes transmitter means responsive to a transmitter enable sig
12. this adequately supports the desired communication function this solution also represents a relatively costly approach There therefore exists a need to provide relatively inexpensive effective and reliable communications for public safety officers and others who ordinarily make use of a vehicle mounted transceiver but who must also carry out operations away from the vehicle from time to time SUMMARY OF THE INVENTION These needs and others are substantially met through provision of the improved mobile radio communica tions system disclosed herein This system makes use of a relatively short range portable transmitter or trans ceiver as the case may be that directly communicates with a secondary mobile unit The secondary mobile unit in turn communicates with the primary vehicle mounted mobile transceiver The secondary mobile unit functions to ensure the propriety of communicating 10 20 25 35 45 50 55 60 with the portable unit and then acts in concert with the primary mobile unit like a repeater to allow communi cation between the portable and the base station The short range needs of the portable unit minimize power requirements and in part allow the portable unit 65 2 to be manufactured and operated in a relatively inex pensive manner In a transmit only configuration the portable unit essentially operates as a cordless micro phone If desired a public address system can be pro vided
13. 158 and an appropriate grounded filter capacitor 159 The collector of the transistor 151 connects through a 2 microfarad coupling capacitor 161 to a voltage divider comprised of a 47 k ohm resistor 162 and an 11 k ohm resistor 163 and also to the base of a 9648 transistor 164 The emitter of this transistor 164 con nects to a 91 ohm resistor 166 The collector of this transistor 164 connects to a 3 3 k ohm biasing resistor 167 and through a 0 1 microfarad coupling capacitor 468 to the limiter deviation adjustment stage 103 The limiter deviation adjustment state 103 includes two grounded parallel configured back to back diodes 4 748 685 7 169 and 171 that provide the limiting function and adjustable 50 k ohm resistor 172 that in combination with a 0 1 microfarad capacitor 173 a 0 005 micro farad capacitor 174 and an appropriate voltage di vider comprised of two resistors 176 and 177 provides the voice deviation adjustment function The output of this stage 103 connects through an appropriate RF choke 178 to a summation node 179 The summation node 179 FIG 105 connects to a data signal unit 181 that comprises a plurality of ca pacitors and resistors configured to receive and shape data signals from the relevant microprocessor either the portable unit microprocessor 801 or the secondary mobile unit microprocessor 701 as the case may be In particular the output from
14. 439 and 0 01 microfarad ca pacitor 441 The collector of this transistor 438 con nects through a 330 ohm resistor 442 to a biased 51 ohm resistor 443 and to a grounded 0 001 microfarad capacitor 444 The collector of this transistor 442 connects to the input of a second 10 7 MHz ceramic filter 446 the output of which connects to a filter comprised of a grounded 22 picofarad capacitor 447 a 20 picofarad 4 748 685 1 coupling capacitor 448 and a grounded 12 micro henry inductor 449 This filter then connects through a 0 001 microfarad coupling capacitor 451 to the input port of an MC3357 low power narrow band FM IF integrated circuit as manufactured by Motorola Inc This integrated circuit provides oscillator mixer limit ing amplifier quadrature discriminator active filter squelch scan control and mute switch functions This integrated circuit 452 provides the second mixer 127 second local oscillator 128 and discriminator 129 functions The MC3357 452 can be configured as de picted with a 10 245 MHz crystal 453 and 455 kHz ceramic filters 454 and 456 to provide the above noted functions and to provide at its output a signal that in cludes the audio and subaudible data signalling as re ceived from the portable unit transmitter 100 This output signal connects through a 1 microfarad capacitor 457 to the amplifier stage 131 This ampli fier includes an LM324 458 the inverting inpu
15. 5 60 65 6 51 to transmit data to the portable unit microprocessor 801 as described below in more detail In an alternative embodiment the portable unit 10 can be configured as a transceiver having a receiver 120 that receives signals transmitted by the secondary mobile unit 51 and that demodulates these received signals to provide data to the portable unit microproces sor 801 and voice signals to an appropriate audio transducer system 802 In another embodiment the portable unit 10 can include additional buttons in the input unit 303 as desired to facilitate remote control of other desired functions such as a public address system on board the vehicle flashing lights on the vehicle sirens on the vehicle and the like Referring now to FIG 9 a block diagram depiction of a transmitter suitable for use in the portable unit 10 or in the secondary mobile unit 51 when the latter is configured as a transceiver can be seen as generally depicted by the numeral 100 The transmitter 100 includes generally a microphone 101 a first amplifier 102 a limiter deviation adjustment unit 103 a sum mation node 104 a frequency modulatable oscillator 106 a second amplifier 107 a filter 108 and an antenna 109 The first amplifier 102 serves to amplify audio signals provided by the microphone 101 which amplified signals are then passed to the limiter devia tion adjustment unit 103 to properly pr
16. 6 of the data processing channel 133 can be connected to an appropriate decoding unit such as a microprocessor to allow proper decoding of the incom ing signal for purposes described below Referring now to FIG 13 a more detailed descrip tion of the receiver 120 will be provided The receiver 120 has an antenna 121 that connects to a preselector circuit 122 that can be comprised of various capacitors and inductors as well understood in the art The preselector 122 functions in accordance with well understood prior art technique to pass only a range of frequencies which range will contain the car rier frequency of interest The output of the preselector 122 connects to a first mixer 123 This mixer includes a voltage divider com prised of first and second resistors 401 and 402 that connects to the base of a 9662 transistor 403 The emitter of this transistor 403 connects through a paral lel connected resistor 404 and 36 picofarad capacitor 406 to the first local oscillator 124 as described be low The collector of this transistor 403 connects through a 12 microhenry inductor 407 to a grounded 0 001 microfarad capacitor 408 and through a 51 ohm resistor 409 to a battery source 411 The collector of the transistor 403 also connects through a coupling capacitor 20 picofarad 412 and past a grounded 22 picofarad filtering capacitor 413 to an IF stage 126 The first local oscillator 124 refe
17. 801 The collector of this transistor 314 also connects to a grounded 10 microfarad capacitor 316 and through a 10 k ohm resistor 317 to the cathode side of the previously noted diode 313 The anode side of this diode 313 connects to a volt age divider comprised of a 20 k ohm resistor 318 and a 10 k ohm resistor 319 This voltage divider connects to the base of a second 9642 transistor 321 The emitter of this transistor connects to ground and the collector connects to a 10 k ohm biasing resistor 322 and further serves as the data input terminal for the portable unit microprocessor 801 So configured the data interface unit 302 serves to provide a reset signal to the portable unit microproces sor 801 as appropriately commanded by the secondary mobile unit 51 as described below in more detail and further serves to detect and provide digitized data to the portable unit microprocessor 801 as modulated with the charging signal The input unit 303 includes a PTT switch 323 and an emergency switch 324 to allow an operator to awaken and properly control the portable unit micro processor 801 The PTT switch 323 connects be tween ground and a parallel connected 0 02 microfarad capacitor 326 and 100 k ohm resistor 327 which in turn connect in series with a 20 k ohm resistor 328 that connects to the positive side of the battery 301 The emergency switch 324 is similarly configured with like numerals
18. 906 This may set by the microprocessor 701 whenever the microprocessor 701 functions to transmit audio from the primary mobile unit 11 via its own transmitter 100 If the message flag has not been set meaning no message has been sent the microproces sor 701 can return to other functions 907 If the message flag has been set however the microprocessor 701 can increment a count 2 908 and then determine whether the portable unit 10 has acknowledged recep tion of the message 909 This presumes of course that the portable unit 10 has been programmed to transmit an acknowledgement code to the secondary mobile unit 51 following receipt of a transmission If the portable has acknowledged receipt of the message the micro processor 701 will clear the message flag 911 clear count 2 912 and terminate transmission of any missed message signals that may have been previously autho rized 913 If however the portable unit 10 has not acknowledged receipt of a message 909 the micro processor 701 will determine if count 2 exceeds a predetermined threshold Y 914 If not the micro processor 701 will return 907 to other preassigned duties If count 2 does exceed the predetermined thresh old 914 however the microprocessor 701 will trans mit a missed message signal 916 and then return 907 So programmed the secondary mobile unit micro processor 701 will support both range burst and
19. ACCEPTED 1008 TRICKLE CHARGE CONTINUES 1009 PORTABLE CONN IECTED 1011 NO FIG 16A U S Patent May 31 1988 Sheet 14 of 16 4 748 685 1014 NO 1013 MOBILE SENDS MOBILE AND PORTABLE BAD CODE SIGNAL USE NEW CODE TfIG T B FIG 17 PORTABLE UNIT OPERATION MICROPROCESSOR OFF MICRO PROCESSOR 1101 CONCLUDE TRANSMISSION U S Patent May 31 1988 Sheet 15 of 16 4 748 685 INCREMENT COUNT 1 3 90 TRANSMIT RANGE BURST 906 901 INCREMENT COUNT 2 PORTABLE ACKNOWLEDGE RECEIVED 914 YES CLEAR COUNT 2 TERMINATE MISSED MESSAGE SIGNAL TRANSMIT MISSED MESSAGE SIGNAL U S Patent May 31 1988 Sheet 16 of 16 4 748 685 922 1 924 SET OUT OF RANGE FLAG 929 ALARM 931 MISSED s MESSAGE YES IGNAL Pala A RETURN 932 FIG 19 4 748 685 1 MOBILE RADIO COMMUNICATIONS SYSTEM TECHNICAL FIELD This invention relates generally to RF communica tions systems and particularly to mobile radio systems The invention also relates to portable radios that may be used with such a mobile radio system BACKGROUND ART RF communications systems are well known in the art In many such systems as in public safety applica tions vehicles are equipped with mobile transceivers that allow public safety officers to communicate with one or more base stations and also with other similarly equipped vehicles i
20. U S Patent UNS UR 1 966 LZEL LZE 626 S O 92 13538 143 226 S 80 m eie 2 9067 T zoe GL OIA 052 L FOr NdNI V S A 3HO 1INS 26214 T 601 U S Patent May 31 1988 Sheet 9 of 16 4 748 685 PRIMARY UNIT TO AUDIO INPUT FOR SECONDARY s xir CONTROL 26 gemi d pe 714 711 IE EEF Cus E dl CONTROL HEAD AUDIO SIGNAL SOURCE SPEAKER 700 FIG 70 TRANSMIT ENABLE 4 748 685 Lap 81 Lez PEE Sheet 10 of 16 fmm gt d umane Kx ss L Sp d SP vOv 707 Tt L _ t Elt oy 331114 ans ae TIT 4 72 OINVH32 vey Ly LG 9 cvv May 31 1988 E w 807 Lez US Patent 31 1988 Sheet 11 0416 4 748 685 U S Patent U S Patent May 31 1988 Sheet 12 of 16 4 748 685 1601 1 601 602 603 14 U S Patent May 31 1988 Sheet 13 of 16 4 748 685 CODE GENERATION PORTABLE DECODES AND BUFFERS NEW CODE 1006 PORTABLE CONNECTED 1007 NO 1006 ODE USEOLDCODE CODE USE OLD CODE VERIFIED YES 1008 NEW CODE
21. United States Patent Rozanski Jr 54 MOBILE RADIO COMMUNICATIONS SYSTEM 75 Inventor Walter J Rozanski Jr Hurst Tex 73 Assignee Motorola Inc Schaumburg Ill 21 Appl No 917 923 22 Filed Oct 10 1986 51 qapya H01B 1 16 52 U S CL aca 455 218 379 63 58 Field of Search 379 63 68 455 33 455 218 35 221 212 381 94 56 References Cited U S PATENT DOCUMENTS 3 092 772 6 1963 Dalton et al 455 221 3 614 321 3 1969 Shaw al 455 221 3 921 074 11 1975 Baird 455 221 4 359 780 11 1982 Day 455 222 4 479 250 10 1984 Flood 455 213 4 525 867 6 1985 Shiratani 455 194 4 541 118 9 1985 Eastmond et al 455 35 4 600 922 7 1986 Dunkerton et al 340 825 44 4 627 101 12 1986 Anderson et al 455 194 OTHER PUBLICATIONS Motorola Service Manual 58P81010C09A PAC RT Portable Mobile Vehicular Repeater System PRESELECTOR FIRST SECOND LOCAL LOCAL OSCILLATOR OSCILLATOR Patent Number Date of Patent 4 748 685 May 31 1988 11 45 Primary Examiner Robert Lev Attorney Agent or Firm Steven G Parmelee 57 ABSTRACT A vehicle mounted mobile transceiver 11 communi cates via a secondary mobile unit 51 with a short range portable unit 10 The portable unit 10 can be either a cordless microphone or a transceiver T
22. bile unit s squelch gate status without re quiring invasive rewiring of the primary mobile unit 11 itself Referring to FIG 10 an embodiment depict ing such a squelch gate detector can be seen as referred to generally by the numeral 700 This squelch gate de tector 700 functions in conjunction with the primary mobile unit 11 and the control head 701 associated therewith The primary mobile unit 11 will typically include a discriminator 702 for receiving a carrier signal as pro vided thereto and for extracting the information modu lated thereon The discriminator 702 output signal then ordinarily passes through a volume control switch 703 provided in the control head 701 before return ing to the primary mobile unit 11 where it ususally passes through one or more amplification and or filter stages 704 before reaching a squelch gate 706 The squelch gate 706 responds to a squelch detect 707 which in turn monitors the output of the discriminator 702 to determine the presence of a viable signal in accordance with well understood prior art technique In the absence of a viable signal the squelch detect 707 will cause the squelch gate 706 to prevent the output of the amplifier stage 704 from reaching the audio power amplifier 708 In the presence of a viable signal however the squelch detect 707 will allow the squelch gate 706 to pass the signal to the audio power amplifier 708 which in turn amplifi
23. cordance with well understood prior art technique Referring now to FIG 5 the portable unit 10 can be housed in a small plastic housing 21 having a belt clip 22 to allow easy mounting of the portable unit 10 on the person of the operator The portable unit 10 also includes a PTT button 23 an emergency button 24 and a microphone 26 loop antenna such as those used in personal pagers can be concealed on the inside of the housing 21 In addition and with reference to FIG 6 two battery charging ports 27 can be provided through the hous ing 21 to allow access to a battery and other circuitry described below To complement the charging ports 27 a battery charging HUB 28 FIG 7 can be pro vided having a cavity 29 formed therein for receiving the portable unit 10 and having appropriate conduc tors 81 disposed therein that mate with the charging ports 27 of the portable unit 10 The battery charging HUB 28 can be operably configured in conjunction with the secondary mobile unit 51 as described below in more detail Referring now to FIG 8 the portable unit can be seen as depicted generally by the numeral 10 The por table unit 10 includes generally a portable unit micro processor 801 an input unit 303 a battery charging unit 302 a transmit enable unit 304 a transmitter 100 a microphone 101 and an antenna 109 The portable unit microprocessor 801 receives input signal
24. e portable unit battery 301 resetting of the portable unit microprocessor 801 on command and the transfer of data between the secondary mobile 4 748 685 15 unit microprocessor 701 and the portable unit micro processor 801 To ensure that the secondary mobile unit 51 re sponds only to the portable unit 10 that is specifically assigned to it the portable unit 10 and secondary mo bile unit 51 use a data transmission comprising a plu rality of codes including an ID code a PTT code and an emergency code These codes which may be subau dibly transmitted are newly generated each time the portable unit 10 and secondary mobile unit 51 are physically joined together via the battery charger as described above To ensure accurate creation transmis sion reception and usage of these codes a number of safeguards have been utilized With reference to FIG 17 the code generation pro cess begins with the secondary mobile unit 51 recog nizing that the portable unit 10 has been placed into the battery charging HUB 28 1001 The mobile unit 51 then generates new codes and transmits them 1002 via modulation of the charging signal to the portable 10 The portable 10 decodes the signals and buffers the new codes 1003 If the portable 10 is removed from the charging HUB 28 prior to the time the code transfer process concludes 1004 both units 10 and 51 will default back to the original codes Oth erw
25. epare the audio signal for modulation and subsequent transmission The processed audio signal is then summed with data signals from the relevant microprocessor at the summation node 104 and utilized to modulate the oscillator 106 The modulated carrier signal then passes through the second amplifier 107 and output filter 108 to the antenna 109 that broadcasts the signal Referring now to FIGS 10a 10c a more detailed description of the transmitter 100 will be described The microphone 101 can be provided through use of a crystal microphone such as an MK 1301 when using the transmitter 100 with the secondary mobile unit 51 one would of course substitute an appropriate audio signal coupling mechanism to allow input of the primary mobile unit 11 audio signal output The out put of the microphone 101 connects to an amplifier stage 102 essentially comprised of a buffer section and an amplification section The buffer section includes a 9642 transistor 151 having its emitter connected to ground and its collector connected through a 5 1 k ohm resistor 152 to a switched voltage source 153 and also through a 100 k ohm resistor 154 to the base thereof The base of this transistor 151 also connects to ground through a 100 k ohm resistor 156 and through a 0 02 microfarad capacitor 157 to the output of the microphone 101 In addition the output of the micro phone 101 connects to a 2 2 k ohm biasing resistor
26. es the signal and renders it audible at the speaker 709 Pursuant to this embodiment a switch 711 can be added to allow the input to the amplifier 704 and squelch gate 706 to be switched between the discrimi nator 702 output and a predetermined audio signal source 712 When switched to a first position indi cated in phantom lines by the reference numeral 713 the output of the discriminator 702 will pass through the volume control 703 through the switch 711 and through the amplifier and squelch gate 704 and 706 as described above When switched to a second position 4 748 685 9 as indicated in phantom lines by the numeral 714 however the output of the audio signal source 712 will instead be provided to the amplifier and squelch gate 704 and 706 When switched to the latter position 714 the opera tion of the squelch gate 706 will continue to remain a function of the output of the discriminator 702 as monitored by the squelch detect 707 Therefore the squelch gate 706 will allow the audio signal source signal to pass through to the audio power amplifier 708 and the speaker 709 when the discriminator 702 provides an output indicating the presence of viable signal In the alternative the squelch gate 706 will prevent this predetermined audio signal from reaching the audio power amplifier 708 when the discriminator 702 does not output a viable signal as detected by the squelch detect
27. ever an appropriate alarm 933 can again be provided to the operator The operator can then take whatever actions are appropriate Those skilled in the art will recognize that various modifications and changes could be made to the above described embodiments without departing from the spirit and scope of the invention For example instead of generating both a new PTT code and a new emer gency code the secondary mobile unit 51 could gener ate and transmit to the portable unit 10 a single code to meet the need for a PTT code and the portable unit 10 could invert this code for use as the emergency code The secondary mobile unit 51 of course would be 10 20 25 30 35 40 45 50 55 60 65 18 configured to recognize the inverted PTT code as the emergency code such that it could respond appropri ately Therefore it should be understood that the claims should not be considered as limited to the above de scribed embodiments in the absence of express inclu sion of such embodiments in the claims I claim 1 A remote squelch detect for use with a radio re ceiver having discriminator means for demodulating an incoming signal and for providing at an output thereof a demodulated signal squelch means for responding to said demodulated signal by closing a squelch gate in the presence of a viable demodulated signal and by opening said squelch gate in the absence of a viable demodulated signal signal
28. gnal then being provided at an appropriate port 732 at the out put of the discriminator Through provision of the above described embodi ment easily available connections to the existing radio equipment can be made while simultaneously assuring reliable and effective squelch detect and transmission enabling Referring now to FIG 12 a block diagram depiction of a receiver suitable for use in the secondary mobile unit 51 or in a system requiring the portable unit 10 to function as a transceiver in the portable unit 10 can be seen as generally depicted by the numeral 120 The receiver 120 includes generally an antenna 121 a preselector 122 a first mixer 123 for mixing the output of the preselector 122 with the output of a first local oscillator 124 an IF section 126 a second mixer 127 for mixing the output of the IF section 126 with the output of a second local oscillator 128 a discriminator 129 for extracting the information signal contained in the incoming signal an amplifier output stage 131 a voice processing channel 132 and a data processing channel 133 10 5 20 35 45 50 60 65 10 In the secondary mobile unit 51 the output 134 of the voice processing channel 132 can be provided to the audio input port of the primary mobile unit 11 while in the portable unit 10 this output 134 could be connected to an appropriate audio transducer The out put 13
29. going message may be prevented To resolve this in one embodiment the secondary mobile unit occassionally broadcasts a range burst signal If the portable unit does not receive such a range burst signal with a predetermined period of time an out of range alarm can be provided by the portable unit to the user In another embodiment the portable unit can be con figured to provide an acknowledge signal upon receiv ing a message from the secondary mobile unit If the secondary mobile unit does not receive such an ac knowledgement it will broadcast a missed message signal When the portable unit moves back within range it will receive the missed message signal and provide a missed message alert to the user The user can then take appropriate action to ascertain the contents of the message In yet another embodiment the squelch gate for the primary vehicle mounted mobile transceiver can be monitored in a non invasive way to allow appropriate enabling of the secondary mobile unit when transmit ting messages received by the primary vehicle mounted mobile transceiver from the portable transceiver unit To facilitate this a predetermined audio signal can be routed through the squelch gate in the primary mobile and the output to the speaker for the primary mobile can then be monitored for presence of this predeter mined audio signal When receiving a viable signal the squelch gate for the primary mobile will be closed and hence the predete
30. he portable unit 10 allows a remotely positioned operator to transmit messages to a base station 13 To ensure security and reliable operation the portable and vehicle mounted units use digitized codes for ID and instruction pur poses These codes are newly generated from time to time by the vehicle mounted unit and are imparted to the portable unit via a battery charging interface An improved remote squelch detect is also provided The improved remote squelch detect substitutes the normal input to the vehicle primary mounted mobile trans ceiver 11 squelch gate for an audio signal The remote squelch detect can then detect the presence or absence of this input signal at the output of the audio PA for the vehicle mounted mobile transceiver and this detection can be used to enable the secondary mobile unit to repeat the incoming message to the portable unit With less delay than the prior art methods 4 Claims 16 Drawing Sheets 132 VOICE AUDIO PROCESSING OUTPUT 134 133 DATA PROCESSING OUTPUT 136 4 748 685 Sheet 1 of 16 May 31 1988 US Patent NOHVIS 8 HOLIMS A9N393383 JINGON 06 SW31SAS LINN NION ASUVGNOO3S LINN AYYNIHd LIND 0245 LINQ STIIHONW LINN e JXTHV LSOd LINN 3189409 25 0L c DIA NOILLVIS el 4 748 685 Sheet 2 of 16 May 31 1988 U S Patent
31. hree cell nicad battery pack which provides a nominal 3 6 volts can be used Referring now to FIG 16 a battery charging circuit as provided within the portable unit 10 can be seen as generally depicted by the numeral 300 The portable unit 10 side of the battery charging unit 300 includes generally a battery 301 a data interface unit 302 an input unit 303 and a transmitter enable unit 304 4 748 685 13 The data interface unit 302 includes two input ports 306 and 307 that allow the battery charging unit 300 to be electrically connected to a complementary battery charging system in the secondary mobile unit 51 as described in more detail below One of these terminals 806 connects to receive a positive voltage and the remaining terminal 307 connects to ground The data interface unit 302 further includes a Zener diode 308 10 k ohm resistor 309 and 20 k ohm resis tor 311 that connect in series between the positive terminal 306 and ground In addition the positive terminal 306 connects through a series connected 860 ohm resistor 212 and diode 313 to the positive termi nal of the battery 301 The common node between the 10 k ohm resistor 309 and the 20 k ohm resistor 311 connects to the base of a 9642 transistor 314 the emit ter of which connects to ground and the collector of which comprises a reset port that can be connected to the reset input of the portable unit microprocessor
32. ise the portable 10 will verify reception of the new codes by making an appropriate transmission 1007 and continuous trickle charging of the portable unit battery 301 will follow 1008 As soon as the portable 10 is removed from the battery charging HUB 28 1009 the portable 10 will send a signal 51 to the mobile to verify the new codes 1011 If the mobile 51 does not receive the correct new codes within a predetermined period of time 1012 the mobile 51 will sound an audible alert 1013 to let the operator know that the portable 10 has not been charged with correct new codes The operator would then reinsert the portable 10 to allow the pro cess to repeat If however the new codes are received and confirmed by the mobile 51 1014 the mobile 51 sounds n audible signal to confirm receipt of the cor rect codes and the mobile 51 and portable 10 then function with the new codes 1016 By generating new codes with each connection only a small likelihood exists that two different portable units 10 having identical codes will be used in proximity to one another And in the event that such an occurance happened the codes could be simply changed by re peating the above procedure By use of this system inventory and service problems are also minimized since any portable unit 10 in the fleet can be used with any secondary mobile unit 51 in the fleet by following the above process If desired o
33. it microphone 53 and the primary mobile unit 11 via the microphone input port The systems 90 module 52 adds two primary fea tures to a mobile system First the Systems 90 module 52 causes the primary mobile unit 11 to broadcast a subaudible digital signal comprising a unique ID code every time the operator closes the push to talk PTT switch on the microphone 53 In this way a base station 13 equipped to decode the ID code can iden tify the mobile it is communicating with and maintain a record of such proceedings Second the Systems 90 module 52 can detect switching of an emergency switch 50 When switching is sensed the Systems 90 module 52 will cause the ID code for the mobile plus an emergency code to be broadcast to the base station 13 for at least a predetermined period of time or until the base station 13 acknowledges receipt of the signal In this way an operator can press the emergency switch 50 and the primary mobile unit 11 will broadcast this call for help to the base station 13 regardless of what else the operator may do As will be shown below the secondary mobile unit 51 can interface with such a module 52 and thereby allow the portable unit 10 to have benefit of such features as well Referring now to FIG 4 the secondary mobile unit can be seen as generally depicted by the numeral 51 and as configured in conjunction with a Systems 90 module 52 The secondary mobile unit 51 inc
34. ludes generally an antenna 54 which may be comprised of the micro phone cord 54 for the primary mobile unit 11 a receiver 120 a secondary mobile unit microprocessor 1701 a battery charging unit 1731 and a watchdog timer 1732 As will be described below in more detail the re ceiver 120 receives both voice and data signals from the portable unit 10 and then functions to separate these signals to thereby provide the voice signal 702 directly to the Systems 90 module 52 where it can serve as the audio input to the primary mobile unit 11 The data signals 1703 from the portable unit 10 are provided to the secondary mobile unit microprocessor 1701 provided for example through use of an MC146805F2 as manufactured by Motorola Inc The microprocessor 701 functions to decode and act upon the incoming data signals and will function 4 748 685 5 either to enable PTT switch the Systems 90 module 52 by providing an enable PTT signal 1704 or to enable transmission of an emergency signal via the Sys tems 90 module 52 through provision of an enable emergency signal 1706 The microprocessor 1701 can also provide encoded data and reset signals as de scribed below to the battery charging unit 1731 for use in providing new communication codes to the portable unit 10 Finally the watchdog timer 1732 may be utilized to assure regular proper operation of the microprocessor 1701 in ac
35. n The data modulation unit 356 includes an input port 372 for receiving data signals from the secondary mobile unit microprocessor 701 This input 372 con nects through a 10 k ohm resistor 373 to connect to the base of a 9642 transistor 374 the emitter of which connects to ground and the collector of which connects to the positive battery charger terminal 362 So con figured data signals as provided by the microprocessor 701 are modulated with the charging signal These data signals can be interpreted by the data interface unit 302 of the portable unit battery charger unit 300 for subsequent use by the portable unit microprocessor 801 as described below By turning the data transmission transistor 374 in the secondary mobile unit battery charger 350 on and off the corresponding data sense transistor 321 in the portable unit battery charger circuit 300 will similarly be switched on and off In this way digitized data can be transferred over the battery charger circuit to the portable unit microprocessor 801 where the informa tion can be decoded and appropriately buffered and acted upon The diode 313 in the portable unit battery charger of course functions to protect the battery 301 from discharging when this data transfer occurs As a direct result of the above configuration the two battery charger connections between the portable unit 10 and the secondary mobile unit support trickle charge for th
36. n the system Such a mobile based system typically includes a vehicle mounted trans ceiver a microphone a control head and an antenna In addition a base station communicates with the vehicle mounted equipment and typically serves as a message dispatch center As the situation may require repeaters may be provided to extend the effective range between the mobile and base station all as well understood in the art The above configuration works well so long as the public safety officer or other individual remains in the vehicle Once the officer moves beyond the operational range of the microphone however the officer typically loses the ability to forward communications to the base station Since the range of the microphone will usually be governed by the length of the microphone cord and since this cord must usually be relatively short commu nications remote from the vehicle are usually rendered difficult if not impossible To meet this problem portable transceivers can be used to allow the officer to be able to communicate with the base station when separated from the vehicle The portable transceiver must in order to be effective emu late the vehicle mounted system in all relevant aspects including frequency capabilities power rating and sig nalling capabilities In effect a public safety service that implements this system must provide two wholly and independently functioning radio systems for each of its vehicles Though
37. nal for receiving at least a part of said demodu lated signal and for using said demodulated signal to modulate a carrier signal wherein said remote squelch detect and transmitter enable device comprises A audio signal source means for providing an audio signal B switch means for selectively connecting said squelch means to said discriminator means output and to said audio signal source means and C signal detect means for detecting the presence of said audio signal subsequent to passage of said audio signal through said squelch means such that said signal detect means will provide said transmit ter enable signal whenever said switch means con 4 748 685 19 nects said audio signal source means to said squelch means and said squelch gate is closed 4 remote squelch detect device for use with a receiver wherein said receiver includes signal detection means for detecting the presence and absence of a received viable signal and squelch means responsive to said signal detection means for opening a squelch gate in the absence of a viable received signal and for closing said squelch gate in the presence of a viable received signal said remote squelch detect device comprising t 10 15 20 25 30 35 45 50 55 60 65 20 A audio signal source means for providing a test signal B switch means for selectively connecting said squelch means to said audio signal source means and C
38. nly the ID need be renewed with each connection To ensure yet greater security however the PTT code and the emergency code referred to above can also be generated anew each time the second ary mobile unit 51 also generates a new ID code for the portable unit 10 In this way each mobile portable pair will not only have a new randomly generated ID code each time they are paired but also new and pre sumably unique PTT and emergency codes This as sures greater security and a smaller likelihood that one mobile portable pair will interfere in the operation of other mobile portable pairs During use of the above described system and with reference to FIG 18 the portable unit microprocessor 701 will ordinarily be off 1101 If the operator pushes 0 20 25 5 40 60 65 16 the emergency button 24 the microprocessor 701 activates and determines that the emergency button 24 was the button that was closed 1102 If the button 24 has been pushed a predetermined number of time such as twice or three times within five consecutive seconds 1103 the portable unit 10 sends a subaudible emer gency code to the secondary mobile unit 51 for a predetermined period of time 1104 such as ten sec onds This signal can be used as described above by a properly programmed mobile unit such as a Motorola MDC 600 equipped unit to toggle and function in an emergency broadcast format This means that
39. on of such 65 a device in the United States For example the portable unit 10 can only transmit on one of eight frequencies 169 445 MHz b 169 505 MHz 170 245 MHz 170 305 10 20 25 30 35 40 45 50 60 4 MHz 171 045 MHz 171 105 MHz 171 845 MHz or 171 905 MHz The maximum output power cannot exceed 50 milliwatts and the maximum emission band width cannot exceed 54 kHz It should be noted that these particular frequencies may give rise to data recep tion problems since adjacent frequencies can be used for hydrological and meteorological data transmissions as used by the power petroleum forest products busi ness and railroad radio services Therefore care must be taken to ensure that the portable unit 10 will not only meet the above noted specifications but that the system will also remain relatively immune to interfer ence problems from adjacent channels Referring now to FIG 3 the secondary mobile unit 51 that interfaces between the portable unit 10 and the primary mobile unit 11 essentially comprises a radio receiver or transceiver when used with a porta ble transceiver as explained below in more detail In practice the secondary mobile unit 51 can be mounted for example inside the housing or another radio interface product such as a Systems 90 module 52 model number HLN106 as manufactured by Mo torola Inc The Systems 90 module 52 connects be tween the primary mobile un
40. on the vehicle to allow return messages to be audibly broadcast to the portable user In a transceiver configuration of course return messages could be re turned directly to the portable unit via a two way link with the secondary mobile unit The portable unit includes a battery to support its portable function To reduce maintenance and enhance reliability the battery can be regularly recharged The secondary mobile unit can have a battery charging cir cuit that functions to recharge the portable unit battery whenever the portable unit is connected thereto To ensure that the secondary mobile unit and the portable unit recognize the legitimacy of each other s communications subaudible digital codes are transmit ted therebetween as necessary To minimize mainte nance these codes are freshly generated and exchanged each time the portable unit and the secondary mobile unit are physically joined In one embodiment these codes are generated by the secondary mobile unit and transmitted to the portable unit via the battery charger circuit In another embodiment the battery charger circuit can be controlled to allow a microprocessor in the secondary mobile unit to reset a microprocessor on board the portable unit When both the portable unit and the secondary mobile unit are transceivers the possibility exists that the portable unit may move out of range of the secondary mobile unit and that an incom ing message may be missed or that an out
41. referring to similarly valued and configured components So configured closing either switch 323 or 324 will provide a strobe signal at an interrupt strobe output 329 that is used to activate the portable unit micro processor 801 in accordance with well understood prior art technique In addition the microprocessor 801 can examine both a PTT sense input 331 and the emergency sense input 332 to ascertain which switch 323 or 324 has been closed and thereby ascertain what action is required The transmitter enable unit 304 includes a 9643 transistor 333 that has an emitter connected to the positive terminal of the battery 301 and a collector connected to provide the switched voltage source to the transmitter 100 described above The base of this transistor 333 connects through a 5 1 k ohm resistor 334 to the collector of a 9642 transistor 336 the emitter of which connects to ground and the base of which connects through a 20 k ohm resistor 337 to an 50 60 65 14 appropriate output enable port of the portable unit mi croprocessor 801 So configured the portable unit microprocessor 801 can enable the transmitter 100 by allowing the battery 801 to provide power to the transmitter 100 compo nents with continued reference to FIG 16 the secondary mobile unit battery charging circuit can be seen as gen erally depicted by the numeral 350 This battery charg ing circuit 350 includes a connec
42. rmined audio signal can be detected When detected the transmit function for the secondary mobile unit can be enabled to allow transmission of the signal being received by the primary mobile 4 748 685 3 BRIEF DESCRIPTION OF THE DRAWINGS These and other attributes of the invention will be come more clear upon making a thorough and complete study and review of the following description of the 5 best mode for carrying out the invention particularly when reviewed in conjunction with the drawings wherein FIG 1 comprises a block diagram depiction of the invention FIG 2 comprises a block diagram depiction of the invention FIG 3 comprises a block diagram depiction of the interface between the secondary mobile unit and the vehicle s communication system 15 FIG 4 comprises a perspective view of the portable unit FIG 5 comprises a bottom plan view of the portable unit FIG 6 comprises a detailed perspective view of the battery charging hub FIG 7 comprises a block diagram depiction of the portable unit FIG 8 comprises a block diagram depiction of a transmitter suitable for use in the invention FIGS 9 a 9 c comprise a schematic diagram of the transmitter FIG 10 comprises a schematic depiction of the trans mit enable feature of the invention FIG 11 comprises a block diagram depiction of a receiver suitable for use in the invention FIGS 12 a and 12 5 comprise a schematic diagram of the receiver
43. rred to above in cludes a crystal 414 that connects between ground and through a series connected inductor 416 and 27 pico farad capacitor 417 to the base of a 9932 transistor 418 The base of this transistor 418 also connects to a voltage divider comprised of an 82 k ohm resistor 419 and 20 ohm resistor 421 and to a series con nected 150 picofarad capacitor 422 and 91 picofarad capacitor 423 A common node between these two capacitors 422 and 423 connects to the emitter of the transistor 418 and also to an 820 ohm grounded resis tor 424 The collector of this transistor 418 connects through a variable inductor 426 to a grounded 0 005 microfarad capacitor 427 and to a biased resistor 428 In addition the collector of this transistor 418 con nects to a grounded 57 picofarad capacitor 429 and also through a 1 picofarad capacitor 431 to a grounded variable inductor 432 The latter inductor 432 con nects to a grounded 47 picofarad capacitor 433 and to the first mixer 123 described above The IF stage 126 includes a 10 7 MHz ceramic filter 434 the input of which connects to receive the output of the first mixer 123 and the output of which connects to a voltage divider comprised of a 2 k ohm resistor 436 and a 390 ohm resistor 437 The voltage divider connects to the base of an M9662 transistor 438 the emitter of which connects to a grounded parallel con figured 360 ohm resistor
44. s from the input unit 303 as operated by the operator The input unit 803 comprises the PTT but ton 23 and the emergency button 24 referred to above The microprocessor 801 responds to these switches by causing the transmit enable unit 304 to enable the transmitter 100 In the ordinary operating mode the microprocessor can literally be turned off in order to minimize current drain and extend battery life When the operator pushes either button related cir cuitry activates the microprocessor and strokes an inter rupt to cause the microprocessor to determine which button was pushed and to react accordingly If the PTT button has been pushed an appropriate PTT code is transmitted subaudibly by the portable to the mobile for a predetermined period of time such as two seconds This allows the mobile to identify the portable this normally requires around 642 milliseconds and for the base station to decode and acknowledge the mobile If the PTT button remained closed beyond the two sec onds the portable continues to send the PTT code Otherwise a termination of message signal may be sent The battery charging unit 302 allows a battery not shown to be charged when the portable unit 10 is in the battery charging hub 28 described above The battery charging unit 302 also allows the portable unit microprocessor 801 to be reset by the secondary mo bile unit 51 and to allow the secondary mobile unit 20 35 45 5
45. t 11 to the base station 13 Referring now to FIG 15 a watch dog timer circuit for use by the secondary mobile unit 51 can be seen as depicted generally by the numeral 500 The watch dog timer 500 receives a tickle signal from the secondary mobile unit microprocessor 801 at an appropriate input 501 This input connects through a 0 1 micro farad capacitor 502 to a grounded 6 k ohm resistor 503 and a series connected diode 504 and 1 k ohm resistor 506 This resistor 506 in turn connects to the base of a 9642 transistor 507 having a grounded emit ter The collector of this transistor 507 connects to a voltage divider comprised of two 10 k ohm resistors 808 and 509 that are biased by a 5 volt source This 5 50 60 65 volt source also biases a parallel connected 1 microfarad capacitor 511 and 51 k ohm resistor 512 that connect to the base of the transistor 507 The voltage divider connects to the gate of a 9577 PUT 513 The cathode of the PUT 513 connects to ground and the anode connects to provide a reset output signal to the second ary mobile unit microprocessor 801 In addition this output 514 connects to a biased 51 k ohm resistor 516 and a grounded 10 microfarad capacitor 517 It will be recalled that the portable unit 10 operates with battery power For ease of maintenance and to increase reliability this battery can be made recharge able In particular a Panasonic P11AA t
46. t of which connects through a series connected 20 k ohm resistor 459 and 5 k ohm resistor 461 to receive the incoming signal and with a common node between these two resistors 461 and 459 being connected to a grounded 0 022 microfarad capacitor 462 The invert ing input of the LM324 458 also connects through a parallel configured 330 k ohm resistor 463 and 0 0039 microfarad capacitor 464 to the output thereof The noninverting input of the LM324 458 connects to a grounded 10 microfarad capacitor 466 and to a volt age divider comprised of a 36 k ohm resistor 467 and 18k ohm resistor 468 that is biased between ground and a positive 5 volt source So configured this section provides both amplification and deemphasis The output of this amplifier stage 131 branches into both a voice processing path 132 and a data processing path 133 The voice processing path 132 essentially comprises a high pass filter followed by a buffer circuit More particularly the input to the voice processing path 132 connects through a 0 022 microfarad capaci tor 469 a grounded 18 k ohm resistor 471 a 0 022 microfarad capacitor 472 and a 0 022 microfarad ca pacitor 473 to connect to the noninverting input of an LM324 474 The noninverting input of the LM324 474 also connects to a grounded 120 k ohm resistor 476 and responds operably to the collector of a 9642 transistor 477 the emitter of which connects to
47. the microprocessor passes through a 20 k ohm resistor 182 to a grounded 0 05 microfarad capacitor 183 Next the signal traverses a 36 k ohm resistor 184 and a 0 02 microfarad capacitor 186 Finally after passing through a 51 k ohm resistor 187 the signal reaches a parallel grounded 7 8 k ohm resistor 188 and 500 picofarad capacitor 189 to then pass through a varactor 191 to reach the summation node 179 The summation node 179 also connects through two series connected capacitors 192 and 193 to the base of an M9932 transistor 194 that comprises a part of the oscillator 106 The oscillator 106 further includes a resistor 196 that attaches to the emitter of the transis tor 194 and an adjustable inductor 197 and parallel connected 57 picofarad capacitor 198 that connect between the collector of the transistor 194 and the switched power supply 153 In addition the base of the transistor 194 connects to the local a frequency determining network 111 which comprises a series connected crystal 199 a variable inductor 201 and a 36 picofarad capacitor 202 that are biased between ground and the base of the transistor 194 The collector of the transistor 194 comprises the output of the mixer 106 and connects through a 2 picofarad coupling capacitor 203 to the amplification stage 107 The amplification stage 107 includes a grounded variable inductor 204 and a 120 picofarad capacitor
48. the pri mary mobile unit 11 will send a predetermined emer gency code to the base station 13 to alert the base station 13 to an emergency involving the operator This signal includes ID information and the like to allow the base station operator to ascertain who the emergency involves To aid in preventing false trigger ing of the emergency function the secondary mobile unit 51 could be programmed to require receipt of three consecutive emergency signal detections from the portable unit 10 which three detections would ordi narily require about one and a half seconds before act ing as set forth above If the operator pushes the PTT button 23 the mi croprocessor 701 causes a subaudible PTT code to be transmitted to the secondary mobile unit 51 for at least a predetermined period of time such as two seconds 1106 and also for so long as the PTT button 23 remains pushed 1107 As described above this PTT code is used by the secondary mobile unit 51 to enable providing voice transmissions from the portable unit 10 to the primary mobile unit 11 for transmission to the base station 13 When both the portable unit 10 and the secondary mobile unit 51 are configured as transceivers addi tional operating concerns become applicable For in stance due to the limited range of the portable unit 10 the likelihood exists that the portable unit 10 will be carried out of reception range of the secondary mobile
49. tion to the vehicle battery 351 that connects through a 920 ohm resistor 852 to a portable unit sense unit 853 a reset com mand unit 854 and a data modulation unit 856 The portable unit 353 sense unit includes a series connected 6 8 volt Zener diode 357 a 10 k ohm resis tor 858 and a 4 7 volt Zener diode 359 The output 361 of the portable unit sense unit 353 provides signal to the secondary mobile unit microprocessor 701 indicating when the portable unit 10 has been connected to the battery charging terminals 362 and 363 of the secondary mobile unit charging HUB 28 described above The reset command unit 354 includes an input 364 for receiving an appropriate reset signal from the sec ondary mobile unit microprocessor 701 that connects through a 10 k ohm resistor 366 to the base of a 9642 transistor 867 The emitter of this transistor 367 con nects to ground and the collector connects through a 10 k ohm resistor 368 to the base of a 9643 transistor 969 and also through second 10 k ohm resistor 371 to the vehicle s battery which also connects to the emitter of the 9643 transistor 369 The collector of the latter transistor 369 connects to the positive battery charger terminal 362 and functions to provide a relatively large signal to the portable unit battery charger unit 300 that causes the data interface unit 302 to provide a reset signal at the output port identified therei
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