Maxon Telecom SM-2000 User Manual
SM-2000
SERVICE MANUAL
MAXON AMERICA, Inc.
10828 N. W. Air World Drive
Kansas City, MO 64153
Phone 816-891-6320 Fax 816-891-8815
680-100-0045 Revision C ECO 98017
December 98
MAXON SM-2000 MOBILE
TABLE OF CONTENTS
TABLE OF CONTENTS
Table Of Contents....................................................i
Specifications........................................................1
Transceiver Nominal Performance ......................................1
General ...........................................................1
Transmitter ........................................................2
Tx Tone Modulation Characteristics .....................................4
Sub Audible Tones - DCS .............................................4
Receiver...........................................................4
Rx Tone Demodulation Characteristics...................................5
Accessories ........................................................5
Reliability Analysis ..................................................5
Programmer ........................................................5
Introduction ........................................................6
Unpacking Information ...............................................7
General Description ..................................................8
Description Of Controls ...............................................9
Theory Of Operation .................................................11
RF Section (SM-2150/VHF) ...........................................13
RF Section (SM-2450/UHF) ...........................................17
PLL ..............................................................20
Test Setup ..........................................................21
SM-2150/VHF Alignment Procedure ....................................22
Alignment Points Diagram (SM-2150/VHF) ..............................26
SM-2450/UHF Alignment Procedure ....................................27
Alignment Points Diagram (SM-2450/UHF) ..............................31
Component Replacement..............................................32
Surface Mount Components ...........................................32
Surface Mount Removal ..............................................32
Surface Mount Component Replacement .................................33
Surface Mounted Integrated Circuit Replacement ..........................33
Parts List Common to SM-2000 ........................................34
Electrical Parts List Main Board Digital Section (SM-2000) .................35
Electrical Parts List Band Chart (SM-2150/VHF) .........................37
Electrical Parts List Main Board (SM-2150/VHF) .........................38
Electrical Parts List Band Chart (SM-2450/UHF) .........................42
Electrical Parts List Main Board (SM-2450/UHF) .........................44
Component Pinout (SM-2000)..........................................48
Voltage Charts (SM-2150/VHF) ........................................51
Voltage Charts (SM-2450/UHF) ........................................54
Trouble Shooting Chart (SM-2000) .....................................57
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December 98
MAXON SM-2000 MOBILE
TABLE OF CONTENTS
Schematics and Block Diagrams ........................................59
SM-2150/VHF Front End Schematic ....................................59
SM-2450/UHF Front End Schematic ....................................59
SM-2000 TCXO Schematic ...........................................59
MA-4472 Microphone Schematic .......................................60
SM-2000 Control Head Schematic ......................................60
SM-2000 Block Diagram .............................................61
SM-2000 Digital Schematic ...........................................62
SM-2150/VHF RF Schematic ..........................................63
SM-2450/UHF RF Schematic ..........................................64
PCB Layouts ........................................................65
SM-2000 Control Head PCB Layout ....................................65
SM-2150/VHF PCB Layout ...........................................66
SM-2450/UHF PCB Layout ...........................................67
SM-2000 Exploded View ..............................................68
SM-2000 Exploded View Parts List .....................................69
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December 98
MAXON SM-2000 MOBILE
SPECIFICATIONS
SPECIFICATIONS
TRANSCEIVER NOMINAL PERFORMANCE
Performance Specifications ..............................FTZ 17TR2049 July 88
TIA/EIA-603
IEC 68 Series
EC 529 IP54
MIL STD 810 C,D,E
RF Output Power ......................................25 W
Modulation Type.......................................G3E/F3E (PM/FM)
Audio power ..........................................4W
Intermediate frequencies ................................45 MHz
455 kHz
Number of Channels....................................4
Frequency Source......................................Synthesizer
GENERAL
Power Supply..........................................13.2 VDC nominal CEPT
15.6 VDC maximum (extreme)
10.8 VDC minimum (extreme)
13.8 VDC nominal TIA/EIA-603
Temperature Range
Storage ...............................................
80°C Maximum; -40°C Minimum
(Extreme)
Operating (to spec) .....................................
25°C Nominal;
60°C Maximum; -30°C Minimum
(Extreme)
Current Consumption
DC Current
Standby (Muted) < 140 mA
Unmuted
25% Max. AF power
50% Max. AF power
100% Max. AF power
Transmit
1 Watt RF power
3 Watts RF power
25 Watts RF power
< 350 mA
< 450 mA
< 570 mA
1.6 A
2.4 A
6.7 A
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December 98
MAXON SM-2000 MOBILE
SPECIFICATIONS
Switching range TX and RX (without re-tuning)
Operational Bandwidth
BAND
MIN MAX MIN MAX
VHF Band 1 136 162 136 162
VHF Band 2 148 174 148 174
UHF Band 1 400 430 400 430
UHF Band 2 420 450 420 450
UHF Band 3 440 470 440 470
UHF Band 4 470 490 470 490
UHF Band 5 490 512 490 512
TX RX
Channel spacing .......................................25 kHz / 20 kHz / 12.5 kHz
programmable
(25 kHz - 12.5kHz switchable
by CPU control)
Dimensions (in/mm)....................................2(H) x 7(W) x 6.25(D)
45(H) x 157(W) x 140(D)
Weight 3lbs, 6oz/ 1.6kg (with mic)
TRANSMITTER
Tests methods are ETS 300 086 Jan
1991 unless stated
Performance Without Sub audible Modulation
Carrier Power @ nominal conditions
Max. Rated Output Power ...............................25 W +/-10% nominal
25 W +2/-3 dB @ extreme conditions
across switching range
Hi Switched by CPU ...................................
Continuously adjustable
Low Switched by CPU ..................................
Continuously adjustable
Frequency stability (SM-2150) ...........................+
Frequency stability (SM-2450) ...........................+2.5 ppm (+ 0.00025%)
Peak audio frequency deviation
(across switching range)
1–25W
1–3W
5.0 ppm (+ 0.00025%)
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December 98
MAXON SM-2000 MOBILE
SPECFICATIONS
Channel Spacing
Without sub audible tone
modulation
(kHz)
25 + 5.0 kHz + 5.0 kHz
12.5 + 2.5 kHz + 2.5 kHz
Audio characteristic ....................................(Method as FTZ 17 TR 2049 July 1988)
MOD Type G3.........................................Within +1/-3 dB of 6 dB/octave
MOD Type F3 .........................................Within +1/-3 dB of 6 dB/octave
Adjacent channel power
25 kHz
12.5 kHz
With sub audible tone modulation
@ 10% peak deviation
MAX DEV
pre-emphasis curve:
300 Hz – 2.55 kHz for 12.5 kHz
Channel Spacing
300 Hz – 3 kHz for 20 , 25 kHz
Channel Spacing
pre-emphasis curve:
300 Hz – 2.55 kHz for 12.5 kHz
Channel Spacing
300 Hz – 3 kHz for 20 , 25 kHz
Channel Spacing
<70dBc
<60dBc
TX spurious emissions (conducted)
9 kHz – 1 GHz
1 – 4.0 GHz
TX spurious emissions (radiated)
9 kHz – 1 GHz
1 – 4.0 GHz
TX spurious emissions (radiated)
9 kHz – 1 GHz
1 – 4.0 GHz
Modulation limiting characteristics .......................Method as FTZ17 TR2049 July 1988
Transmitter audio distortion (without CTCSS) ..............Method as FTZ17 TR 2049 July 1988
1 kHz modulation input < 5 %
Transmitter audio distortion (with CTCSS) .................Method as EIA RS 220A Mar 79
Audio frequency 1 kHz
Any CTCSS frequency combined
Hum & noise (residual modulation) ........................>40dB
< -36 dBm
< -30 dBm
< -36 dBm
< -30 dBm
< -36 dBm
< -30 dBm
=75% peak deviation
<8%
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December 98
MAXON SM-2000 MOBILE
SPECIFICATIONS
TX TONE MODULATION CHARACTERISTICS
Sub audible tones - CTCSS
Tone range ............................................67 – 250 Hz @ 0.3 % accuracy
Tone standard .........................................RS-220A EIA Standard
Non-standard tones.....................................50 – 260 Hz @ 0.3 % accuracy
Nominal tone deviation..................................10 % peak system deviation
SUB AUDIBLE TONES - DCS
Tone standard .........................................Normal and inverted
Nominal tone deviation..................................10 % peak system deviation
RECEIVER
Performance without sub audible modulation...............Method ETS 300-086 JAN 1991
unless stated
Sensitivity 12 dB SINAD ................................< - 118 dBm
Amplitude characteristic ................................+ 3dB
Co-channel rejection
25 kHz
12.5 kHz
Adjacent channel selectivity
25 kHz
12.5 kHz
Spurious response rejection .............................> 70 dB (100 kHz - 4 GHz)
Intermodulation response rejection
+
(25 kHz & 50 kHz)
+ (50 kHz & 100 kHz)
Blocking
+ 1 MHz
+ 5 MHz
+ 10 MHz
RX spurious emissions (conducted)
9 kHz – 1 GHz
1 GHz – 4.0 GHz
RX spurious emissions (radiated)
9 kHz – 1 GHz
1 – 4.0 GHz
<-6dB
<- 10 dB
> 70 dB @ nominal conditions
> 60 dB @ nominal conditions
> 65 dB (3 generator method)
>85dB
>85dB
>85dB
-57dBm
-47dBm
-57 dBm
-47 dBm
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December 98
MAXON SM-2000 MOBILE
SPECIFICATIONS
AF power.............................................5 W maximum @10% Distortion into a
4 ohm load. 4 Watts nominal.
AF frequency response ..................................Method as FTZ 17 TR 2049 July 1988
MOD Type G3.........................................Within +1/-3 dB of 6 dB/octave
de-emphasis curve
300 Hz – 2.55 kHz for 12.5 kHz
Channel Spacing
300 Hz – 3 kHz for 25 kHz
Channel Spacing
MOD Type F3 .........................................Within +1/-3 dB of 6 dB/octave
de-emphasis curve
300 Hz – 2.55 kHz for 12.5 kHz
Channel Spacing
300 Hz – 3 kHz for 25 kHz
Channel Spacing
RX Hum & Noise ......................................>40dB
RX TONE DEMODULATION CHARACTERISTICS
Subaudible tones - CTCSS/DCS
CTCSS tone range .....................................67 Hz to 250 Hz
CTCSS tone standard...................................RS-220A EIA Standard
CTCSS non-standard tones ..............................50 – 260 Hz
DCS tone standard .....................................Standard and inverted
Decode Sensitivity ......................................Method: Decrease signal level @ 10%
peak deviation
All tone ...............................................<= 9 dB SINAD
Environmental ........................................IEC529 level IP54 MIL STD 810C
EMC.................................................EMC Directive 89/336/EEC May 1989
ETS 300.279
ACCESSORIES
MA4472 Microphone
RELIABILITY ANALYSIS
Calculation method
MTBF................................................15,000 Hr. MIL-HDBK-217F. Ground
benign. Parts stress method.
MTTR ...............................................30 Min. (Average time to rework any
SMD component & reassemble).
PROGRAMMER
.....................................................SMP4004C
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December 98
MAXON SM-2000 MOBILE
INTRODUCTION
INTRODUCTION
Advanced state-of-the-art technology is used in the design and manufacturing of the SM-2000 Mobile. The
Phase Lock Loop (PLL) synthesizer provides more flexibility and capability in the SM-2000 Mobile. This
scanning mobile has 4 channel capability. It offers CTCSS, DCS, scanning, priority channel, and many other
functions. All these functions are controlled by the micro controller. The micro controller reads specific
channel information from an Electronically Erasable Programmable Read Only Memory (EEPROM).
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December 98
UNPACKING INFORMATION
Check the carton carefully for the following items:
1 Transceiver Unit
2 Microphone
3 DC Power Cord
4 Mobile Mounting Bracket
5 Assembly Hardware
6 Operating Guide
MAXON SM-2000 MOBILE
UNPACKING INFORMATION
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December 98
MAXON SM-2000 MOBILE
GENERAL DESCRIPTION
GENERAL DESCRIPTION
The Maxon SM-2000 is a rugged two way FM mobile radio which operates from 136-174 MHz (VHF) in
two bands & 400-512 MHz (UHF) in five bands. The SM-2000 is a synthesized radio utilizing
microcomputer technology to provide reliable high quality simplex two-way mobile communications. The
SM-2000 transmitter output power level is 25 watts over a wide bandwidth, with a receiver operational
bandwidth that covers the specified frequency band. The basic radio package includes the following
features:
Microprocessor Control
•
Synthesized RF Channel Selection (Frequency Control)
•
CTCSS Encode / Decode
•
DCS Encode / Decode
•
Priority Channel Scan
•
5 PPM Frequency Stability (SM-2150/VHF)
•
2.5 PPM Frequency Stability (SM-2450/UHF)
•
• Field Programmable with PC
Internal 4 watt speaker, with Volume Control
•
• Busy Channel Lockout
The small size of the SM-2000 radio makes it ideal for front mounting in conventional vehicles. The radio
is operated with a simple hand held microphone in combination with the operating controls described in the
following section.
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December 98
MAXON SM-2000 MOBILE
DESCRIPTION OF CONTROLS
DESCRIPTION OF CONTROLS
Figure 1 SM-2000 Front Panel
DESCRIPTION OF CONTROLS
The controls, indicators and microphone/programming connector are located on the front panel. The
Monitor and Auxiliary buttons are located on the radio’s front panel. The following table details the
Mobile controls, indicators, and connections.
TABLE 2
Controls, Indicators, And Connections
ITEM FUNCTION
1. Channel Select Switch
2. ON/OFF Volume Control
3. Microphone Connect Jack Used to connect the microphone to the mobile
4. Busy/Call/TX Tri-colored LED indicator
5. Auxiliary (AUX) Switch Used for control of after market accessories
6. Monitor Switch When pushed, monitors the chosen channel
7-10. Channel Indicator LED’s Indicates the channel when illuminated
Rotary switch, used to select one of 4 channels (max.) and to engage
scanning function
Main power switch and volume control. Fully counter clockwise is off
position
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December 98
MAXON SM-2000 MOBILE
DESCRIPTION OF CONTROLS
Rear Panel Connections
ITEM FUNCTION
1. Antenna Connector ( S0-239 ) 50 ohm connector
2. DC Power Connector
3. External Speaker Connector
Used to connect the mobile to the power supply 13.2 VDC or 13.8 VDC
U.S.A.
Multipurpose socket used to connect to a remote speaker or for test
connection
Figure 2 SM-2000 Rear Panel
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December 98
MAXON SM-2000 MOBILE
THEORY OF OPERATION
THEORY OF OPERATION
Each of the Scanning Mobile radios, UHF & VHF, include a unique main P.C.B. consisting of RF, Digital
and Analog circuitry.
DIGITAL CIRCUITRY
IC 411 and IC412 are digitally-controlled analog switches which internally consist of three single pole,
double throw switches. By placing a high (5V) or low (0V) on the control lines which consists of A,B, and
C. “A” controls the X ports “B” controls the Y ports and “C” controls the Z ports. Example: A high on
control “A” would connect X to X1. A low on control “A” would connect X to X0.
CTCSS/DCS Decode Circuits
Discriminator audio from Pin 9 of IC 109 is fed to IC 406 and associated parts, which are the first 2 poles
of a 6th order 250Hz Chebeyshev low pass filter. The output from Pin 1 (IC406A) is fed into IC411 (Pin 2)
and output to Pin 15 (IC411). The signal is then fed to Pin 8 (IC407) which is a 6th order low pass
Butterworth switched capacitor filter. The output from the Butterworth filter (Pin 3 IC407) is then fed to
the remaining 4 poles of the 6th order Chebeyshev, which consist of IC 406C and one of the two
operational amplifiers internal to IC407 (MF6-100) along with associated components. Both the
Chebeyshev and the Butterworth combines for a 4dB ripple low pass filter when programmed for 250Hz.
The output of IC406C(Pin 8) is fed into the remaining operational amplifier internal to IC407 (MF6-100)
which forms the squaring circuit for the Decode signal. The signal is output from Pin 2 IC407 (MF6-100)
and fed into IC409 (micro) where it is matched with a preprogrammed frequency. If successful a Decode
occurs, which is shown by a green L.E.D. on the front panel of the UHF Scanning Mobile and audio is
heard. If valid Decode was not seen, the busy L.E.D. (Yellow) would be shown.
CTCSS/DCS Encoder Circuit
During TX encode the tone squelch digital signal is produced as a 3-bit parallel word at Pins 15 (A), 16
(B), and 18C of the micro controller (IC409). The 3-bit digital signal is converted to an analog signal by
resistors R427, 428, and 430. The analog signal is fed into IC411 Pin 1. The signal is output on Pin 15
(IC411) and fed into Pin 8 of IC407 (6th order Butterworth clock tuned low pass filter). The filtered
encode output from Pin 3 (IC407) is fed into Pin 13 (IC411) and output on Pin 14 (IC411).
The filtered encode signal is fed to IC405B and RV403 (sub-audible gain control), the output of IC405B is
then fed to the audio mixer circuit.
Channel Select Circuit
One of 4 channels may be selected using the channel switch on the front panel. The channel switch SP4T
(single pole 4 throw) with output to 4 channel LED’s and to diode’s to be converted to an inverted 4-Bit
binary code. The binary code inverted is equal to the channel number. The binary code is decoded by the
micro controller enabling the appropriate RX or TX frequency and associated data to be selected from the
EEPROM.
•
NOTE:It is possible any one of the 4 channel locations can be a scanning position. Refer to
Operators Manual for further instructions.
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December 98
MAXON SM-2000 MOBILE
THEORY OF OPERATION
EEPROM
RX/TX channels, CTCSS/DCS as well as other data from the programmer are stored in the EEPROM. The
data stored is retained without power supplied. This is a non-volatile memory. The EEPROM may have
information re-programmed or erased. IC408 is an EEPROM with 2048 (256x 8) bit capacity and data is
written and read serially, with the Programming cable through the front panel microphone connector.
High Pass Filter
The high pass filter is an 8-pole .1dB chebeyshev active filter that comprises IC410 and associated
components. The de-emphasis is provided by resistor R451 and capacitor C452. Receive audio is passed
to IC410 by Pin 4 of IC411 where sub-audible tones below 250Hz are removed. Mic audio is also fed into
IC410 via IC411 (Pin 4) where sub-audible voice products below 250Hz are also removed.
Mute (Squelch) Circuit
The mute circuit which is controlled by the output of IC409 (micro) pin 77 (386) is connected to Q409 via
R438 which opens analog gate IC401D and mutes the audio path to the AF amplifier, in conjunction with
Q137 shorting the input to audio amp IC108.
TX Audio and Filter Circuits
Microphone audio from front panel (via IC412), is fed into IC401A, and into IC404B (Pin 6). The TX
audio is output on Pin 7 (IC404B) and into the high pass filter (IC410), where sub-audible voice products
are removed. The TX audio output from IC410 is fed into IC404A&B which with associated parts form a
pre-emphasis mic amplifier and limiter. The output from Pin 1 IC404A is fed to RV402 (TX Modulation
Level Adjust) and fed into IC404C&D with associated parts to form a 3kHz low pass filter. The output of
IC404D (Pin 14) is then fed into the Audio Mixer Circuit.
Audio Mixer and Inverter
IC405A is an audio mixer where audio and sub-audible tones are combined. RV403 is used as a level
control for the Sub-audible tones. This level is summed with amplified, pre-emphasized, and limited audio
and feed to IC405A, which is an inverting amplifier. The output is fed to the VCO and TCXO to provide
the necessary modulation signal.
Analog Ground Supply
IC406D supplies analog ground (2.0V) to all operational amplifier circuits except for IC405A and IC405D.
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December 98
MAXON SM-2000 MOBILE
THEORY OF OPERATION
PLL
IC101 (MC1459IF) is a PLL frequency synthesizer with an on-board 1.1 GHZ divide by 64/65 dual
modulus prescaler. In addition to the prescaler and frequency counters, the synthesizer IC has a a phase
detector and a C register (Configuration register) that allows certain functions to be configured as desired.
The synthesizer is serially controlled by three wire input to the IC. Serial data is fed to pin 19 of the IC.
Serial data CLK (pin 18) and active low ENABLE (pin 17) are the input pins that allow data transfer into
the integrated circuit for control and frequency selection.
Data transfer is byte-oriented and may be shifted in 1, 2 or 3-byte patterns. One byte (8 bits) accesses the C
or configuration register, two bytes (16 bits) access the R register and 3 bytes (24 bits) access the A
register.
Internally the synthesizer has three counters used as frequency dividers. These counters are the R,A and N
counters. The R counter is actually controlled by 3 bits of the R register while the remaining 13 bits
determine the divide by R value. The frequency at pin 20 (12.8 MHz) is divided by R to determine the
frequency steps of the PLL synthesizer. In programming the radio, 5.0 kHz or 6.250 kHz step sizes can be
selected for any channel.
The 24- bit A register controls the N and A (prescaler) counts. Together these counts determine the total
synthesizer divide ratio affecting the f
values. A8-A19 are the N counter values. A21 and A20 must always be set high. A23 and A22 are both
set to 0 which controls the function of output A and causes it to be a port. This port, output A, is used to set
TX power high or low. A high output on port A sets transmit power low.
(frequency input) signal from the VCO. A0-A7 are the A counter
in
The 8-bit C register performs control functions as stated:
C7 sets polarity of the phase detector bits. Logic “0” is normal.
C6 determines the phase detector used. A logic “0” selects theta V and theta R outputs
C5 enables the lock detector when its logic is “1”.
C4 when a logic “1”, puts CMOS sections in standby mode.
C3 and C2 set phase detector current at the PD output. Not used in this application.
C1 is the value present at Output A.
C0 is the value present at Output B.
Transistors Q101 through Q104, along with related resistors and capacitors, connect the dual pin theta V
and Theta R outputs intoa2mAcurrent source that is powered by a 20V DC to DC converter. This allows
the tuning voltage to be approximately 3 to 17 VDC.
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December 98
MAXON SM-2000 MOBILE
THEORY OF OPERATION
RF SECTION (SM-2150/VHF)
VHF Transmitter
The Transmitter is comprised of:
1. Microphone Audio Circuit
2. Transmitter Stage and Harmonic Filter
3. Automatic Power Control
4. Frequency Synthesizer Circuit
Microphone Audio Circuit
Microphone audio from the digital circuitry is amplified, pre-emphasized, limited, and mixed with
Sub-Audible and applied to the VCO at Pin 1, through RV101, to balance VCO and TCXO modulation.
Transmitter Stage and Harmonic Filter
When in the transmit mode of operation the diode D103 is forward biased enabling the RF signal to pass to
the pre-driver Q118 by Q116 and Q117. The amplified RF signal is amplified again by Q120. The
amplified RF signal passes through the stripline coupler and is fed to the harmonic low pass filter,
comprising of L128, L130, L131, and L132, capacitor 271, 273, 275, 277, and 283 and then to the antenna
connector (ANT). The stripline coupler provides a sample of the RF signal for the automatic power
control. During transmit D107 is forward biased which connects the power amp, D120, to the antenna.
D120 is forward biased inhibiting transmit signal power from being fed to the receiver circuitry.
Automatic Power Control
The automatic power control contains the stripline coupler, diode D107 and variable resistor VR104,
IC104A, and three transistors Q123, Q124, and Q125. IC104A forms a differential amplifier. The RF
signal present in the coupler is rectified by D107, to produce a DC voltage proportional to RF power which
is applied to Pin 3 of IC104A. TX 8.5V is also applied to the input of IC104A via the potential divider
R168, VR104, and R170 at pin 2. The different signal at output of IC104A is passed to Q124 and Q125 to
produce a constant power output to the antenna connector (ANT). VR104 is used to adjust the RF high
power level. VR105 is used to set the low power setting.
RX & TX Voltage Controlled Oscillator Circuit
The circuit contains two VCO’s. One for producing carrier frequencies during transmit and one for
producing the local oscillator frequency during receive. The circuit also has RX and TX power line filters.
RX & TX Power Line Filters
Transistors Q353 and Q354 are configured as TX5v and RX5v power supply ripple filters respectively.
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December 98
MAXON SM-2000 MOBILE
THEORY OF OPERATION
RX VCO
The RX VCO comprises JFET Q351, coil L356 and varactor D353 and is configured as a Colpits oscillator.
D353 produces a change in frequency with a change in DC voltage and is controlled by the phase detector
signal present at the anode. The local oscillator signal at the drain of Q351 is applied to RF out of the
module when diode D103 is reverse biased and D104 is forward biased. L356 is used for PLL alignment.
TX VCO
The TX VCO comprises JFET Q352 coil L353 and varactor D352 and is configured as a colpits oscillator.
The AF signal at MOD port is applied to the cathode of D352. The control voltage from the loop filter is
applied to the drain of Q352 and is passed to the power amplifier and harmonic filter via the buffer Q113
and Q114. When diode D103 is forward biased and D104 is reversed biased L353 is used for PLL
alignment.
Loop Filter
Transistor Q101 to Q104 and associated components form a loop filter. The phase detector from Pin3 and
4 of IC101 are filtered to remove any reference frequency harmonics and applied to the voltage controlled
oscillator.
PLL Frequency Synthesizer
The PLL frequency synthesizer (IC101) contains an oscillator for the reference divider, a programmable
divider, a phase/frequency Comparator and an out of lock detector and a Prescaler.
Reference Oscillator
The reference oscillator of IC01 along with a 10.25 or 12.8MHz TCXO, varactor diode D701 and D702,
and the thermistors TH701, TH702, and TH703 produce a temperature compensated 10.25 or 12.8MHz
reference.
Programmable Dividers
The serial frequency data (DATA) is received by the data programmable divider at Pin 19 of IC101 from
Pin 1 of IC409 (Micro controller) out. The internal Prescaler divided input frequency at pin 11 of IC1 is
further divided by the programmable divider. The 10.25 or 12.8MHz TCXO frequency at pin 20 is the
reference divider to produce a reference frequency of 5 or 6.25kHz respectively. The internal
programmable divided frequency (Fv) and the reference frequency (Fr) are fed to the internal phase
detector.
Phase Detector
The phase detector produces negative pulses when Fv < Fr, positive pulses when Fv>Fr. When Fv = Fr and
phase is the same, the phase detector presents a high impedance at Pin 4. The signal at Pin 2 is applied to
the VCO via the loop filter.
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December 98
MAXON SM-2000 MOBILE
THEORY OF OPERATION
Out of Lock Detector
The out-of-lock detector produces a high logic level when Fr and Fv are in the same phase and frequency,
low logic level pulses when the loop is out-of-lock at Pin 2 of IC101. The signals at Pin 2 of IC101 are
buffered by Q106 and then integrating by R114 and C122. The product of the integrating circuit is fed to
L/D port.
Prescaler
The internal Prescaler of IC101 divides the incoming signal frequency from the VCO via input pin 1 by 64
or 65. The divided VCO frequency is passed to the 6-stage A counter and 12-stage N counter.
Receiver
The receiver uses Dual Conversion Superheterodyning techniques, it is comprised of:
1. RF amplifier
2. First Mixer and First IF Amplifier
3. Second Mixer, Second IF Amplifier and FM Detector
4. Receiver Audio Circuit
5. Mute (squelch) Circuit
RF Amplifier
The signal received via the antenna is routed through the 9th chebyshev low-pass filters containing
capacitors C273, C275, C277, C280, C283 and coils L128, L130, L131, L132, and is passed through the
front-end module (RF amplifier) via pin 1. The front-end module contains L800 to L806 and Q800. The
front-end module is configured to enable the RF signal at the operating frequency to pass the first mixer.
First Mixer and First IF Amplifier
The VCO local oscillator signal routed through buffer transistor Q113 and Q114 is filtered by C164, C165,
C281, C310, and L110, L123. IC102 produces a difference frequency IF of 45MHz from pin 6 of the
front-end module and the filtered VCO local oscillator signal at pin 1. The 45MHz difference frequency is
filtered by the 2-pole crystal filter CF101. The tuned circuit T101 and T102 and associated components
provide matching of the crystal filter to insure good band-pass response and selectivity. The IF signal is
amplified by Q130 and passed to the second mixer, second IF and FM detector IC109.
Second Mixer, Second IF and FM Detector
A signal conversion FM receiver integrated chip, IC109 contains the second mixer, second IF and FM
detector functions. The second local oscillator frequency is determined by the crystal X101 connected to
pin 1 of IC109. The IF signal is received at pin 16 of IC109 via R203 and coupling capacitor C182. The
second IF frequency of 455kHz is produced when the different frequency is applied to the mixer via Pin 6.
The output of the second mixer via Pin 3 is applied to a 455kHz band-pass filter, CF104 for 25kHz and
CF103 for 12.5kHz channel spacing. The output of CF104 is passed to a high gain IF amplifier (limiter) in
IC109 via Pin 5. The amplified signal is coupled to the adjustable quadrature detector T103. Any detected
signal is produced at Pin 9 of IC109 and applied to the Receiver Audio Circuit and the Mute (Squelch)
Circuit.
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MAXON SM-2000 MOBILE
THEORY OF OPERATION
Receiver Audio Circuit
The receiver audio circuit is comprised of a low pass filter and an audio amplifier on the RF PCB.
Low Pass Filter
The low pass filter is configured from coil L227, capacitor C201 and resistor R206.AF signals from Pin 9
of IC109 are filtered by the low pass filter to remove any components of the 455kHz IF signal. The filtered
is passed to the high pass filter.
High Pass Filter
The de-emphasized audio signal from the high pass filter is fed to the audio amplifier (IC108).
Audio Amplifier
IC108 is the audio amplifier. The audio signal is passed to IC108. The gain of the amplifier is set by
resistor R153. The amplified audio signal at Pin 4 of IC108 is applied to the external speaker.
Mute (Squelch) Circuit
The squelch circuit switches off the audio power amplifier in the absence of audio signal. The squelch
circuit comprises a 50kHz pass band filter, squelch control (RV103) and a noise detect circuit.
The audio signal from Pin 9 of IC 109 is filtered by the 50kHz bandpass filter formed by L228, L229,
C191, C192, and C193. The noise in the IF pass band is accepted, frequencies in the voice frequency band
are rejected and noise present at the output of the filter is applied to the noise detect circuit via RV103.
RV103 is used to adjust the squelch sensitivity.
Noise Detect Circuit (SQ Board)
The noise detect circuit in conjunction with IC109 consists of transistor Q133 and Q132, thermistor TH101
and diode D125. Any noise signal present is applied to the base of Q133 of the SQ circuit from Pin 11 of
IC109. The signal is amplified by Q133 rectified by D11 and then buffered by Q132. The buffered signal
output is applied to the squelch trigger of IC109 Pin 12 via resistor R200. The squelch trigger out put (Pin
13 of IC109) is applied to the Micro controller on the Digital circuit. When noise is present, the voltage at
Pin 12 of IC109 exceeds 0.7V, the squelch trigger output is 0V (logic0) muting the receiver audio circuit.
When no noise is present the voltage at Pin 12 of IC109 is less than 0.7 and Pin 13 of IC109 is at 5V
(logic1), unmuting the audio circuit.
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MAXON SM-2000 MOBILE
THEORY OF OPERATION
RF SECTION (SM-2450/UHF)
UHF Transmitter
The Transmitter is comprised of:
1. Microphone Audio Circuit
2. Transmitter Stage and Harmonic Filter
3. Automatic Power Control
4. Frequency Synthesizer Circuit
Microphone Audio Circuit
Microphone audio is pre-emphasized, limited and mixed with sub-audible tones to provide the modulating
signal for the transmitter. This combined modulation is applied to TCXO modulation pin 1 and also to the
VCO modulation input via RV101 to effect 2-point modulation. RV101 is a modulation balance control
that equalizes modulation sensitivities of the two oscillators.
Transmitter Stage and Harmonic Filter
Power Amplifier IC103 is an RF Module. In transmit, diode D103 is forward biased allowing the RF signal
to pass to the input of IC103 via Q116 and Q117. The amplified RF output passes through the stripline
coupler and is fed to the harmonic low pass filter, consisting of spring coils L118, L120, L121 and L125
and capacitors C271, 273, 275, 277 and 280, and then to the antenna connector. The stripline coupler
provides a sample of the RF signal for automatic power control. During TX, D108 connects the power amp
to the antenna. D120 and D121 are forward biased reducing transmit signal power at the receiver input.
Automatic Power Control
The automatic power control contains the stripline coupler, diode D107, and variable resistor RV104, op
amp IC104 , and two transistors: Q124 and Q125. IC104 acts as a differential amplifier. The RF signal is
rectified by D107 to produce a DC voltage, proportional to RF power, that is applied to IC404 pin 3.
Voltage divider R168, RV104 and R170 monitors TX 8.5V dc to develop a reference for IC104A pin 2.
The difference at the output of (IC104 pin 1) is passed to Q124 and drives the collector of Q125. This
feedback controls the gain of IC103 to maintain a constant RF power output. RV104 is used to adjust the
RF high power level. RV105 is used to set the low power setting.
Frequency Synthesizer Circuit
With data received from the EEPROM ( IC408 ) the frequency synthesizer circuit controls and produces
the RF carrier frequency for the transmitter during transmit and the local oscillator frequency for the
receiver.
The frequency synthesizer circuit is comprised of:
1. RX and TX voltage controlled oscillator module.
2. Loop Filter
3. PLL Frequency Synthesizer
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MAXON SM-2000 MOBILE
THEORY OF OPERATION
Voltage Controlled Oscillator Circuit
The circuit produces carrier frequencies during transmit and local oscillator frequencies during receive.
Transistor Q107 is configured as a power supply ripple filter. The VCO utilizes transistor Q108, varactor
D101 , D102 and trimmer capacitor TC101 . These components are configured as a Colpitts oscillator.
D101 and D102 produce a change in frequency with a change in DC voltage and are controlled by the
phase detector. Q110 and Q111 are an amplifier and buffer for the output of the oscillator.
Receiver
The receive signal passes through the low pass filter, then onward to pin 1 of the Front End module. A
bandpass filter consisting of C801-C810 (see band chart for different band values) and L801-L803 is
coupled to the base of Q801 (2SC5084) which is the RF amplifier. Diode D801 serves as protection from
static and RF overload from nearby transmitters. The output of Q801 is coupled to a second bandpass filter
consisting of C812-C824 and L804-L807. The output of the Front End ( pin 6) is coupled to the double
balanced mixer IC102. The receiver Front End Module is factory pre-tuned and requires no field
adjustment. Repair is effected by replacement of the entire (properly banded) module. Frequency bands are
listed in the SPECIFICATIONS section of this manual.
The receiver Front End module pin-outs are:
1. RF Input
2. Input Ground
3. Ground
4. Receive +5VDC
5. Output Ground
6. RF Output
First Mixer
IC102 is a Double Balanced Mixer which provides a 45MHz intermediate frequency output. The filtered
frequency from the Front End is coupled to signal input pin3 of the mixer. The Local Oscillator from the
VCO module runs 45MHz lower than the receive frequency and is coupled to IC102 at pin6. The resultant
IF output exits at mixer pin2. The 45MHz IF output is matched to the input of the 4 pole monolithic crystal
filter by C179 , L119 , C172 and C173 . The crystal filter provides a bandwidth of + and - 7.5kHz from the
operating frequency for the signal providing a high degree of spurious and intermodulation protection.
Additionally, a 90MHz trap is placed at the filter input to provide additional attenuation of the second order
IMD (Intermodulation Distortion). The output of the filter is impedance matched by T101 , C175 , and
C176 to the base of the post filter IF amplifier Q130 ( MMBC1321 ).
Second Oscillator- Mixer- Limiter and FM Detector
The output of IF amplifier Q130 is coupled through C182 to the input of IC109 (Pin16), an MC3371
device. IC109 is a monolithic single-conversion FM receiver containing a mixer, the second local
oscillator, limiter and quadrature detector. The second local oscillator is crystal-controlled by X101 and
operates at 44.545 Mhz. Mixing the second L.O. with the 45.0 Mhz IF input signal provides a resultant 455
kHz signal at the second mixer output. The mixer output is then routed to CF103 (455HT) for channel
spacing of 12.5 kHz or to CF104 (455F) for channel spacing of 20 or 25kHz. These ceramic filters provide
adjacent channel selectivity for the desired bandwidths. Selection of CF103 or CF104 is software controlled
and programmable on a channel to channel basis.
Filter selection is performed by Q135, D126 and D126. The selected filter output drives a high gain
limiting amplifier that is internally coupled to the quadrature detector. Refering to the RF schematic, with
Channel Spacing low, Q135 is off and CF104 is the selected filter.
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