Maxon SD-125 Series User manual

SD-125
Maxon America, Inc. 10828 N.W. Airworld Dr. Kansas City, MO 64153 Tel: [phone] Fax: [phone]
Part Number: 680-100-2004
October 1998
SERVICE
MANUAL

TABLE OF CONTENTS
TABLE OF CONTENTS ............................................................i
SPECIFICATIONS ................................................................1
UNPACKING.....................................................................7
INTRODUCTION .................................................................8
FEATURES ......................................................................8
THEORY OF OPERATION ........................................................9
INTRODUCTION ...............................................................9
DIGITAL CIRCUITS ............................................................9
RF CIRCUITS ..................................................................9
RF CIRCUITS PLL SYNTHESIZER ...............................................10
RECEIVER ...................................................................10
MAINTENANCE AND REPAIR....................................................12
GENERAL....................................................................12
REMOVING & REPLACING THE UPPER COVER ..................................12
REMOVING & REPLACING THE DIGITAL BOARD & SHIELD PLATE ...............12
REMOVING & REPLACING THE RF BOARD......................................13
PROGRAMMING ................................................................14
ALIGNMENT PROCEDURE ......................................................14
RECEIVER ...................................................................14
TRANSMITTER ...............................................................14
TEST EQUIPMENT SETUP .......................................................17
ALIGNMENT POINTS DIAGRAM .................................................18
COMPONENT REPLACEMENT...................................................19
TROUBLESHOOTING GUIDE ....................................................20
VOLTAGE CHART ..............................................................21
SD-125 DIGITAL BOARD (COMMON) PARTS LIST (650-010-0029) ....................25
SD-125 (U1 400-430MHz) RF BOARD PARTS LIST (650-020-0027) ......................27
SD-125 (U2 440-470MHz) RF BOARD PARTS LIST (650-020-0026) ......................30
SD-125 (V2 148-174MHz) RF BOARD PARTS LIST (650-020-0029) ......................33
COMPONENT PINOUT ..........................................................37
WIRING DIAGRAM .............................................................41
SCHEMATICS, BLOCK DIAGRAM & PCB’s........................................43
BLOCK DIAGRAM ............................................................43
DIGITAL BOARD SCHEMATIC .................................................44
RF BOARD (148-174MHz) SCHEMATIC ..........................................45
RF BOARD (400-430MHz) SCHEMATIC ..........................................46
RF BOARD (440-470MHz) SCHEMATIC ..........................................47
TCXO SCHEMATIC ...........................................................48
VCO (148-174MHz) ............................................................48
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MAXON
SD-125 RF LINK MODULE

VCO (400-430MHz) ............................................................49
VCO (440-470MHz) ............................................................49
FRONT-END (148-174MHz) .....................................................50
FRONT-END (400-430MHz) .....................................................50
FRONT-END (440-470MHz) .....................................................50
POWER AMPLIFIER (148-174MHz) ..............................................51
POWER AMPLIFIER (400-430MHz) ..............................................51
POWER AMPLIFIER (440-470MHz) ..............................................51
DIGITAL PCB ASSEMBLY .....................................................52
RF PCB ASSEMBLY (148-174MHz) ..............................................53
RF PCB ASSEMBLY (400-430MHz) ..............................................54
RF PCB ASSEMBLY (440-470MHz) ..............................................54
EXPLODED VIEW & PARTS LIST.................................................55
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MAXON
SD-125 RF LINK MODULE

SPECIFICATIONS
GENERAL
Equipment Type .......................................Data radio
Performance Specifications ..............................TIA / EIA-603 & ETS 300-113
Band .................................................UHF / VHF
Channel Spacings ......................................25 kHz, 12.5 kHz programmable
RF Output Power ......................................5/1 watt
Modulation Type.......................................F3D, F3E
Intermediate Frequency .................................45.1 MHz & 455 kHz
Number of Channels....................................16
Frequency Source......................................Synthesizer
Operation Rating ......................................Intermittent
90:5:5(Standby: RX: TX)
Power Supply..........................................Ext. Power Supply(12 VDC Nominal Voltage)
9.0V - 15.0V DC EXTREME
Temperature Range
Storage ...........................................from - 40°C to + 80°C
Operating .........................................from - 30°C to + 60°C
Current Consumption
Standby (Muted)...................................<65mA
Transmit 5 Watts RF Power .........................< 2.0 A
Transmit 1 Watt RF power .........................< 1.0 A
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October 98
MAXON
SD-125 RF LINK MODULE

Frequency Bands:
RX TX
VHF: V1 136.000 - 162.000 MHz 136.000 - 162.000 MHz
V2 148.000 - 174.000 MHz 148.000 - 174.000 MHz
UHF: U2 440.000 - 470.000 MHz 440.000 - 470.000 MHz
U1 400.000 - 430.000 400.000 - 430.000
U5 420.000 - 450.000 420.000 - 450.000
U3 470.000 - 490.000 470.000 - 490.000
U4 490.000 - 512.000 490.000 - 512.000
Dimensions............................................(30 mm)H x (62 mm)W x (118 mm)D
Weight ...............................................253 grams
TRANSMITTER
Carrier Power: ........................................Nom. Max Min
Hi...............................................5W < 6W > 4.5W
Low .............................................1W < 1.5W > 0.8W
Sustained Transmission .................................Nominal conditions
Time: 5 10 30 Sec.
Power: >90% >85% >80%
Frequency Error .......................................< 0.5 kHz Nominal condition for VHF
< 0.75 kHz Nominal condition for UHF
±3.0 ppm Extreme condition for UHF
±5.0 ppm Extreme condition for VHF
Frequency Deviation:
25 kHz Channel Spacing ............................Peak ±5.0, Min. ±3.8
12.5 kHz Channel Spacing...........................Peak ±2.5, Min. ±1.9
Audio Frequency Response ..............................Within +1/-3dB of 6dB octave
@ 300 Hz to 2.55 kHz for 12.5 kHz C.S.
@ 300 Hz to 3.0 kHz for 25 kHz C.S.
Adjacent Channel Power
25kHz...........................................< 70 dBc @ Nominal Condition
< 65 dBc @ Extreme Condition
12.5 kHz..........................................< 60 dBc @ Nominal Condition
< 55 dBc @ Extreme Condition
Conducted Spurious Emission............................< -57 dBc
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MAXON
SD-125 RF LINK MODULE

Modulation Sensitivity ..................................100mV RMS @ 60 % Peak Dev.
Hum & Noise:
25 kHz Channel Spacing ............................> 40 dB (with no PSOPH)
12.5 kHz Channel Spacing...........................> 40 dB (with PSOPH)
Modulation Symmetry ..............................< 10 % Peak Dev @ 1 kHz input for nominal dev +20dB
Load Stability .........................................No osc at ³10:1 VSWR all phase angles and suitable
antenna
No destroy at ³20:1 all phase angle
Peak Deviation Range Adjustment @ 1 kHz, Nom. Dev +20dB:
25 kHz Channel Spacing ............................Min. 3.5, Max. 6.0
12.5 kHz Channel Spacing............................Min. 1.5, Max. 4.0
RECEIVER
Sensitivity (12dB Sinad) .................................UHF < -117 dBm, VHF <-118 dBm @ Nom. Condition
UHF < -115 dBm, VHF <-116 dBm @ Extreme Condition
Amplitude Characteristic................................<±3dB
Adjacent Channel Selectivity:
25 kHz Channel Spacing ............................> 60 dB @ Nom., > 55 dB @ Extreme Condition
12.5 kHz Channel Spacing...........................> 50 dB @ Nom., > 45 dB @ Extreme Condition
Spurious Response Rejection.............................70 dB (100 kHz - 4 GHz)
Image Response........................................>70
IF Response ...........................................>70
Others................................................>70
Intermodulation Response Rejection:
±25 kHz/ 50 kHz ...................................65 dB
±50 kHz/ 100 kHz ..................................65 dB
Conducted Spurious Emission @ Nominal Conditions:
9kHz-1GHz.....................................< -57 dBm
1GHz-4GHz.....................................< -47 dBm
RX Spurious Emissions (Radiated) @ Nominal Conditions
9kHz-1GHz.....................................< -57 dBm
1 GHz - 12.75 GHz .................................< -47 dBm
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October 98
MAXON
SD-125 RF LINK MODULE

AF Distortion..........................................< 5% @ Nom., < 10 % @ Extreme condition
RX Hum & Noise:
25.0 kHz CP ......................................< 40 dB No PSOPH
12.5 kHz CP ......................................< 40 dB with PSOPH
Receiver Response Time.................................<16mS
Squelch Opening Range: ................................RF level for 6 to 14 dB Sinad
Squelch Closing Range (Hysteresis):.......................0-6dBSinad @ Nominal Condition
Squelch Attack Time:
RF Level at Threshold ..............................<40mS
RF Level at Threshold + 20 dB .......................<30mS
Squelch Decay Time ....................................5 mS Min., 20 mS Max.
Antenna Socket Input Match.............................> 10 dB Return Loss
L.O. Frequency Temperature Stability ....................1st < 5 ppm, 2nd < 15 ppm from -30° to + 60° C
L.O. Frequency Aging Rate ..............................±2 ppm/ year
REFERENCE CRYSTAL
Frequency ............................................12.8 MHz
Holder Type...........................................HC-18
Temperature Characteristic .............................±5.0 ppm from -30° C to +60° C
Aging Rate ............................................< 2 ppm/ year in 1st year
< 1 ppm/ year thereafter
Lock Time ............................................<10mS
TXtoRX.............................................< 20 (No Power Saving)
RXtoTX.............................................<20
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MAXON
SD-125 RF LINK MODULE

ENVIRONMENTAL (performance without degradation unless stated)
Temperature ..........................................deg C
Operating.............................................-30° to +60° C Degradation Specified @ Extreme
Storage ...............................................-40° to +80° C
Recharging............................................-10° to +55° C
ESD..................................................20 kV (C-MIC ³15 kV)
Vibration .............................................MIL STD 810 C Procedures I, II, V and IEC68 26
PROGRAMMER
Programmer (Interface Module) ..........................ACC-2000
Programmer (Interface Cable) ...........................QPA-4000
Programmer (Software) .................................ACC-900
•Due to continuing research and development the company reserves the right to alter these specifications without prior
notice.
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MAXON
SD-125 RF LINK MODULE

Intentionally Left Blank
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MAXON
SD-125 RF LINK MODULE

UNPACKING
The SD-125 RF Link Module is the only item included in the shipping container.
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October 98
MAXON
SD-125 RF LINK MODULE

INTRODUCTION
The Maxon SD-125 Series of RF Link Modules from Maxon
utilizes the latest technology in its design and manufacturing.
Both the UHF and VHF models are PLL (Phase Lock Loop
Synthesizer) / microprocessor controlled, and offer one to five
watts of power with 16 channel capability. Multiple functions
including 1200 to 9600 baud rates, AC and/or DC audio
coupling, GMSK and FSK modulation are standard in these
fully programmable wide bandwidth RF Link Module units.
The radio is programmed using a IBM®Personal Computer,
DOS®based software, an interface module and a programming
cable. This allows the radio to be tailored to meet the
requirements of the individual user and of the System(s) it is
operating within.
FEATURES
•Busy Channel Lockout
•16 Channels
•TX Time-out
•Power Save
•1 / 5 Watt Programmable Output
•12.5 / 25 kHz Programmable Channel Spacing
Busy Channel Lockout
The Busy Channel Lockout feature, when enabled, disables the
transmitter when the receiving channel is busy and the user
attempts to transmit.
16 Channels
The SD-125 Series radio can store up to 16 channels within the
same band.
TX Time-out
The TX Time-out feature, when enabled, limits the amount of
time that the user can continuously transmit. This time can be
set in increments of 10 seconds from 10 seconds to 990
seconds.
Power Save
The Power Save feature is used when an external battery is used
as the power source. When Power Save is enabled, the receiver
“ON” and “OFF” time can be programmed into the radio and
allows the operator to set the length of time the receiver is
asleep.
.
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October 98
MAXON
SD-125 RF LINK MODULE
Maxon's SD-125

THEORY OF OPERATION
INTRODUCTION
The VHF and UHF radios are comprised of two PCB's (an RF
PCB and a digital PCB). These boards are connected with an 18
pin female and male connector . The digital board is interfaced
with external data equipment through the 9 pin d-sub male
connector, which controls the radio and data receiving and
sending .
DIGITAL CIRCUITS
The Digital circuit contains the CPU, the channel select switch,
and associated digital circuits.
TX-SIGNAL CIRCUIT
The TX data signal comes from Pin 2 of Con 401, and goes
through U404D. The TX-signal is amplified by U406C. The
TX-signal is filtered by U405A & B which is a 4'th order low
pass filter, the output of U405A is then fed to the RF board for
TX modulation.
RX-SIGNAL CIRCUIT
The RX- data signal comes from the RF board, which is
connected with pin 10 of Con 403. The RX-signal is switched
by U404A and adjusted by RV403 and amplified by U407. The
amplified signal goes to pin10 of Con 401.
RSSI DETECTOR
From the RF board, the RSSI (Received Signal Strength
Indicator ) signal flows to U403A & B through R461. The pulse
is injected from pin 5 of U403B every 1 mS and C451 is
discharged. It is then charged by R464. The RSSI signal is
simultaneously input to pin 7 of U403A and those signals are
compared. The compared signal is output from U403A. Pin 1 of
U403A and the CPU detects the pulse width. The pulse width is
varied by RSSI DC voltage, therefore, the carrier detection is
controlled by the CPU.
EEPROM
RX / TX channel and RSSI detection level 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. U402 is an EEPROM with 2048 (8 x 256) capacity
and data is written and read serially.
CHANNEL SELECTOR
One of 16 channels may be selected using the Dip Switch
(SW401). SW401 encodes the channel number, selected into
4-bit binary code. The binary code plus one equals the channel
number. The binary code is decoded by the CPU enabling the
appropriate RX or TX frequency and associated data to be
selected from the EEPROM.
DC TO DC CONVERTER
The main DC power is injected to the DC to DC converter . The
DC to DC converter regulates the various input power supply
voltage and outputs a constant voltage of 7.5 Volts. It is a
source for all of the RF and digital circuits.
The DC to DC converter is formed by U801, Q801, Q802, L801
and R804. U801 is a switch mode DC to DC Converter IC.
Input DC various appears as a voltage various through R804.
U801 detects the voltage and controls the switching pulse. As
the switching pulses, Q801and Q802 switches the input DC of
various supply voltages and generates the constant DC of
supply voltage.
RF CIRCUITS
TRANSMITTER
The transmitter is comprised of:
1. Buffer
2. P.A. Module
3. Low Pass Filter
4. Antenna Switch
5. A.P.C. Circuits
BUFFER
VCO output level is -6dBm and amplified to +10dBm (UHF),
+6dBm (VHF). The buffer consists of Q16 and Q17 for
isolation and gain.
P.A. MODULE
The P.A. Module contains Q501, Q502, and Q503. Three stage
amplifier Q501 amplifies the TX signal from +10 dBm to 100
mW. Q502 is amplified to 0.5W. Q503 amplifies to 3W and
then matched to 50 Ohms using the L.C. network, thereby
reducing the harmonics by -30 dB.
LOW PASS FILTER
L7, L8, L11, C72, C73, C74 and C75 are the 7th order
Chebyshev low pass filter. Unwanted harmonics are reduced
by -70 dBc.
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October 98
MAXON
SD-125 RF LINK MODULE

ANTENNA SWITCH
When transmitting, the diodes D5 and D6 are forward biased
enabling the RF signal passage to the antenna. D6 is shorted to
ground inhibiting the RF signal to front end. In receive the
diodes D5 and D6 are reversed biased passing the signal from
the antenna through L13 and C83 to the front end without signal
loss.
AUTOMATIC CURRENT CONTROL (ACC) CIRCUITS
The ACC circuit consists of R109, variable resistor RV1,
IC3(B) and transistors Q21 and Q22. The supply current is
monitored by the difference voltage on R109 (0.1 Ohm). If the
current varies by RF power output or other reasons, it produces
some bias voltage by IC3A and Q19. The differential signal at
the output of IC3 is passed to Q21 and Q22 that produces a
constant power output to the antenna. RV1 is used to adjust the
RF power level.
RF CIRCUITS PLL SYNTHESIZER
12.8 MHz TCXO
The TCXO contains the 3-stage thermistor network
compensation and crystal oscillator and modulation ports.
Compensation is ±5 PPM or less from -30c to +60c.
PLL IC DUAL MODULES PRESCALER
Input frequency of 12.8 MHz to IC2 MC14519 pin 20 is
divided to 6.25 kHz or 5 kHz by the reference counter, and then
supplied to the comparator. RF signal input from VCO is
divided to 1/64 at the prescaler in IC2, divided by A and N
counter in IC2 to determine frequency steps, and then supplied
to the comparator. PLL comparison frequency is 6.25/5kHz so
that minimum programmable frequency step is 5/6.25 kHz.
The A and N counter is programmed to obtain the desired
frequency by serial data in the CPU. In the comparator, the
phase difference between reference and VCO signal is
compared. When the phase of the reference frequency is
leading , Fv is the output, but when VCO frequency is leading,
Fr is the output. When Fv=Fr, phase detector out is a very small
pulse. 64/65 modulus prescaler is comprised in IC2, and has
two output ports:
•Port A pin 16: TX enable 2
•Port B pin 15: prescaler power save control in PLL
IC Pin 13 labeled test2 allows the technician to see
the output of the dual modulus prescaler for trouble
shooting purposes, no connection should be made to
this pin.
LEVEL SHIFTER & CHARGE PUMP
The charge pump is used for changing output signals Fr, Fv at
PLL IC from 0-5v to 0-12v necessary for controlling the VCO.
REFERENCE FREQUENCY LPF
The Loop Filter contains R12, C21 and C22. LPF settling time
is 12mS with 1 kHz frequency. This also reduces the residual
side-band noise for the best signal-to-noise ratio.
DC TO DC CONVERTER
The DC to DC converter convert the 5v to 14-16v to supply the
necessary voltage for wide range frequency in the VCO.
VCO
The VCO consist of an RX VCO and a TX VCO. It is switched
TX/RX by the power source. It is configured as a colpits
oscillator and connected to the buffer as a cascade bias in order
to save power. The varicap diode D201/D301 are
low-resistance elements and produce a change in frequency
with a change in reverse bias voltage (2-11v). L203/L303 are
resonant coils, which changes the control voltage by the tuning
core. D202 modulation diode, modulates the audio signal.
C204 compensates for the non-linearity of the VCO due to
modulation diode, and maintains a constant modulation
regardless of frequency.
RECEIVER
FRONT-END
The receive signal is routed backward through the low pass
filter, then onward to Pin 1 of the Hybrid Receiver Front End
Module to a bandpass filter consisting of (VHF C622 through
C608, L607 through L604 ) and (UHF C601through C610,
L601 through L603 ) is coupled to the base of Q601 which
serves as an RF amplifier. Diode D601 serves as protection
from static RF overload from nearby transmitters. The output
of Q601 is then coupled to a second bandpass filter consisting
of (VHF C607 through C623 and L604 through L607).The
output of Pin 6 is then coupled to the doubly balanced mixer
D9. The receiver front end module is factory pre-tuned and
requires no adjustment. Repair is effected by replacement of
the entire module of the proper banded module. These are VHF
148MHz to 174 MHz and UHF 440 MHz to 470 MHz. The
receiver front end module signal pins are as follows:
1. RF Input
2. Input Ground
3. N/A
4. Receive +5V
5. Ground
6. Output
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October 98
MAXON
SD-125 RF LINK MODULE

FIRST MIXER
D9, T2 and T3 are double balanced mixers which provide the
45.1 MHz intermediate frequency output. The filtered
frequency from the front end module is coupled to T2 . The 45.1
MHz IF output is matched to the input of the 2-pole monolithic
filter by L14, L31, C69 and C97. The crystal filter provides a
bandwidth of ±7.2 kHz from the operating frequency providing
a high degree of spurious and intermodulation protection.
Additionally, a 90 MHz trap (XF1) is also placed at the filter
output to provide additional attenuation of the second order
IMD. The output of the filter is impedance matched by C97 and
C69 to the base of the post of filter IF amplifier Q25.
SECOND OSCILLATOR MIXER LIMITER AND FM
DETECTOR
The output of the post filter amplifier, Q25, is coupled via C98
to the input of IC5 ( MC3371). IC5 is a monolithic single
conversion FM transceiver, containing a mixer, the second
local oscillator, limiter and quadrature detector. Crystal X1
44.645 MHz is used to provide resultant 455kHz signal from
the output of the second mixer. The mixer output is then routed
to CF1 (455F). These ceramic filters provide the adjacent
channel selectivity of 25 kHz bandwidth .
RSSI ( RECEIVER SIGNAL STRENGTH INDICATOR )
The RSSI signal is output from IC5 on pin 13. As the receiver
signals the output, DC voltage is varied as much as receiver
signal strength. Also, the DC signal is temperature
compensated with a thermistor (TH1).
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October 98
MAXON
SD-125 RF LINK MODULE

MAINTENANCE AND REPAIR
GENERAL
When removing or fitting, use the Exploded View and Parts
List, located on page 55 in conjunction with the following
procedures:
•WARNING: Disconnect the SD-125 from all
external equipment at the D-Sub connector prior to
disassembly.
REMOVING & REPLACING THE UPPER
COVER
Removing the Upper Cover:
1. Unscrew the four upper cover mounting screws
located on the upper cover of the radio.
To replace the Upper Cover:
1. Reverse the steps taken to remove the Upper Cover.
REMOVING & REPLACING THE DIGITAL
BOARD & SHIELD PLATE
Removing the Digital Board Assembly & Shield
Plate:
1. Remove the Upper Cover (refer to Removing &
Replacing the Upper Cover).
2. Disconnect the DB9 pin connector on CON401.
3. Unscrew the 4 mounting screws.
4. Remove the Digital Board Assembly.
5. Remove the Shield Plate.
To replace the Digital Board Assembly:
1. Reverse the steps taken to remove the Digital Board
Assembly & Shield Plate.
MAXON
SD-125 RF LINK MODULE
PAGE-12-
October 98
Figure 1-Upper Cover Removal
Figure 2-Digital Board Assembly Removal

REMOVING & REPLACING THE RF
BOARD
Removing the RF Board Assembly:
1. Remove the Upper Cover (refer to Removing &
Replacing the Upper Cover).
2. Remove the Digital Board Assembly and Shield
Plate (refer to Removing & Replacing the Digital
Board Assembly & Shield Plate).
3. Unscrew the 4 mounting standoffs.
4. Unsolder the antenna connector cable.
5. Remove the RF Board Assembly.
To replace the RF Board Assembly:
1. Reverse the steps taken to remove the RF Board
Assembly.
MAXON
SD-125 RF LINK MODULE
PAGE-13-
October 98
Figure 3-Shield Plate Removal
Figure 4-RF Board Removal

PROGRAMMING
The SD-125 Series radio requires the ACC-900 Programming
Software, ACC-2000 Interface Module, 9-15 VDC 200mA
Power Supply and QPA-4000 Programmer Interface Cable.
Refer to the ACC-900 Programming Manual (P/N:
680-110-0032) for detailed information on programming the
SD-125 Series radio.
ALIGNMENT PROCEDURE
The SD-125 UHF/VHF Receiver is by design, broad band
covering UHF(400-430 MHz & 440-470 MHz) and
VHF(148-174 MHz) and should require no special alignment,
unless repairs are performed on the receiver portion.
Should repairs be necessary, use the "Test Equipment
Diagram" on page 17 & the "Alignment Points Diagram" on
page 18, in conjunction with the following procedures:
•An Extender Board (P/N: 650-060-0016) is required
in order to separate the Digital and RF PCB’s to
allow access to the alignment points. Installation
instructions are provided with the Extender Board
Assembly.
RECEIVER
1. Apply a standard test signal to the receiver antenna
terminals.
2. Adjust T1 for maximum sensitivity and audio
output with minimum audio distortion.
3. Adjust RV403 for the specific audio output level.
RX VCO
1. Set the unit to the highest receive frequency,
470MHz(UHF), 174MHz(VHF) and adjust the
VCO L303 to 8 volts.
2. Set the unit to the lowest receive frequency
440MHz(UHF), 148(VHF) and check that the VCO
voltage is above 2.0 volts. If voltage is below 2.0
volts, adjust L303 for 2.0 volts or more.
•Note: Use TP1 to measure the voltage.
TRANSMITTER
Connect the unit to a Service Monitor with the power meter
setting to the 10 W scale (or autorange)
TCXO
Set the channel selector to the mid-range frequency 460 MHz,
adjust TCX01 for a reading of 460 MHz ±200Hz (155 MHz
VHF models).
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October 98
MAXON
SD-125 RF LINK MODULE

TX VCO
1. Set the unit to the highest transmit frequency,
470MHz(UHF), 174MHz(VHF) key the transmitter
and adjust the VCO L203 to 8 volts.
2. Set the unit to the lowest transmit frequency 440
MHz(UHF), 148(VHF) key the transmitter and
check that the VCO voltage is above 2.0 volts. If
voltage is below 2.0 volts, adjust L203 for 2.0 volts
or more.
•Note: use TP1 to measure the voltage.
TX Deviation and Balance Adjustment
1. Set the unit to a mid-frequency and input the TX
data with 400 Hz standard audio level.
2. Increase the signal level to 20 dB from standard
level.
3. Monitor the demodulated signal from service
monitor. Adjust RV3 to make the monitored signal
to be a balanced square wave.
4. Reduce input signal to the standard level and adjust
RV2 for the standard deviation.
APC
1. Adjust RV1 for High Power (5W)
2. Adjust RV6 for Low Power (1W)
3. This completes the transmitter alignment
procedures.
SD-125 Squelch setting using the ACC-2000
Interface Module
Maxon’s wide range of data radio products since the crystal
control module (DM-0500 series) had their squelch level
setting by hardware touch up. With the new SD-125 series, the
squelch level to open or close (unmute or mute) is set up by
software control.
The RSSI utilizes the A/D conversion that will be fed to the
microprocessor, which in turn will use this input to determine
the squelch level setting to control the mute and unmute of the
receiver.
Default setting of squelch level for all the SD-125 from our
manufacture and workshop is approximately set at:
1. Squelch open (unmute) at -114dBm to -113dBm
(0.45 - 0.5mV of the RX signal strength)
2. Squelch close (mute) at -117dBm to -116dBm (0.3 -
0.35mV of the RX signal strength)
Changing the default squelch settings requires use of the
programming adaptor box. This box is designed for use not
only as part of the programming kit but also as a tool of squelch
level setting.
The minimum equipment required for squelch level setting is a
RF signal generator. Radio communication test equipment is
recommended.
1. Power up the programming adaptor box (use the DC
supply of9-15Volts 200mA).
2. Hook up the SD-125 unit to the programming
adaptor box, and its antenna connector to the RF
input port of the RF signal generator.
3. With the adaptor box turned "off”, simultaneously
press and hold both "ON/OFF" and "WRITE" but-
tons down.
4. Release the "ON/OFF" button first then the
"WRITE" button next. (LED indicator on the box
will flash twice after that it may stay on / off, this is
of no concern , because depending on the signal
strength of the RF generator as well as the pre-set
level of squelch the SD125 may be in standby mode
(LED OFF) or in receiving mode (LED ON)
5. Adjust the RF signal generator for the desired signal
strength to OPEN squelch (e.g. default setting is
-113dBm, that is equivalent to 0.5mV)
6. Press and release "READ" button, LED indicator
will flash 3 times then it will be ON.
7. Adjust the RF signal generator for the desired signal
strength to CLOSE squelch (e.g. default setting is
-116dBm, that is equivalent to 0.35mV)
8. Press and release "READ" button, LED indicator
will flash 1 time then it will be OFF.
9. Press and release "WRITE" button, LED indicator
will flash twice.
10. Squelch level is now set. Test for desired level by
increasing or decreasing the RF signal to levels set
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October 98
MAXON
SD-125 RF LINK MODULE

for open and close squelch (mute LED will be OFF &
unmute LED will be ON).
•NOTE: The difference of RF signal strength
between the unmute and mute levels must be greater
than or at least equal to 0.15mV (i.e. at least
-123.5dBm) for the squelch setting to work
properly. If they are too close to one another, RSSI
through the A/D conversion can not differentiate
between the mute and unmute level properly. As a
result, it would cause the CD (Carrier Detect) to act
intermittently.
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October 98
MAXON
SD-125 RF LINK MODULE