Daniels Electronics Ltd. OST-3H035 User manual

DANIELS
ELECTRONICS LTD.
TM
MT-3 RADIO SYSTEMS
ENHANCED AM/FM
SYNTHESIZER
INSTRUCTION MANUAL
OS(R/T)-3(A/H) 29 - 470 MHz
Covers models:
OST-3H035, OST-3H045, OSR-3H061
OST-3A128, OSR-3A149
OST-3H141, OST-3H162, OSR-3H141, OSR-3H162
OST-3H440, OSR-3H440
Copyright ©2000 Daniels Electronics Ltd. All rights reserved. No part of this publication may be
reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic,
mechanical, photocopying, recording or otherwise, without the prior written consent of Daniels
Electronics Ltd.
DE™ is a registered trademark of Daniels Electronics Ltd. registered in the United States Patent and
Trademark Office.
Issue: 3 Previous Issue: 2
Issue Date: March 2000 Previous Issue Date: March 1998 Daniels Electronics Ltd.
Printing Date: March 2000 Victoria, BC.
Part No.: IM10-OS3AH PRINTED IN CANADA

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ii Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz
Reviewed By:
Quality Assurance:
Claudia Boorman _________________
Name Signature Date
NOTE:
The user's authority to operate this equipment could be revoked through any
changes or modifications not expressly approved by Daniels Electronics Ltd.
The design of this equipment is subject to change due to continuous development.
This equipment may incorporate minor changes in detail from the information
contained in this manual.

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Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz iii
TABLE OF CONTENTS Page
1 GENERAL..........................................................................................1-1
1.1 Introduction...................................................................................1-1
1.2 OS(R/T)-3(A/H) Enhanced Synthesizer Family Models ................................1-1
1.3 Performance Specifications.................................................................1-3
1.4 Printed Circuit Board Numbering Convention ...........................................1-4
2 THEORY OF OPERATION......................................................................2-1
2.1 Internal Power and Control (Digital Board)...............................................2-1
2.2 Synthesizer Analog Circuitry (Analog Board)............................................2-1
2.2.1 Common Analog Board Circuitry.......................................................2-1
2.2.2 29 - 71.4 MHz Analog Board Circuitry................................................2-3
2.2.3 118 - 159.4 MHz Multichannel AM Analog Board Circuitry........................2-3
2.2.4 128 - 174 MHz Analog Board Circuitry................................................2-4
2.2.5 406 - 470 MHz Analog Board Circuitry................................................2-5
2.3 Synthesizer Digital Circuitry (Digital Board) .............................................2-6
2.4 Frequency Control...........................................................................2-6
2.4.1 BCD Switch Frequency Control ........................................................2-6
2.4.2 Frequency Select Handle Frequency Control..........................................2-7
2.5 Synthesizer Base and Frequency Increment Table.......................................2-7
2.6 5.0/6.25 kHz Channelization...............................................................2-8
2.7 8.333 kHz Channelization. .................................................................2-8
2.8 12.5 kHz Channelization....................................................................2-9
3 SYNTHESIZER ALIGNMENT.................................................................3-1
3.1 General........................................................................................3-1
3.2 Repair Note ...................................................................................3-1
3.3 Recommended Test Equipment.............................................................3-1
3.4 OS(R/T)-3(A/H) Synthesizer Factory Configuration....................................3-1
3.5 OS(R/T)-3(A/H) Synthesizer Alignment..................................................3-2
3.5.1 General.....................................................................................3-2
3.5.2 Synthesizer Test Points...................................................................3-2
3.5.3 Synthesizer Removal and Installation...................................................3-3
3.5.4 Circuit Board Removal...................................................................3-3
3.5.5 Frequency Adjustment and Channel Selection.........................................3-3
3.5.5.1 VHF OS(R/T)-3H 29 - 71.4 MHz VCO Alignment ...............................3-4
3.5.5.2 VHF OS(R/T)-3A 118 - 159.4 MHz Alignment ...................................3-5
3.5.5.3 VHF OS(R/T)-3H 128 - 174 MHz VCO Alignment...............................3-5
3.5.5.4 UHF OS(R/T)-3H 406 - 470 MHz VCO Alignment...............................3-6
3.5.5.5 Reference Frequency Alignment .....................................................3-6
3.5.6 Jumper Configuration ....................................................................3-6

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iv Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz
4 ILLUSTRATIONS AND SCHEMATIC DIAGRAMS.......................................4-1
4.1 OS(R/T)-3H 29 - 71.4 MHz Analog Board Diagrams .................................. 4-1
4.1.1 OS(R/T)-3H 29 - 71.4 MHz Analog Board Component Layout (Bottom)........ 4-1
4.1.2 OS(R/T)-3H 29 - 71.4 MHz Analog Board Component Layout (Top)............4-2
4.1.3 OS(R/T)-3H 29 - 71.4 MHz Analog Board Schematic Diagram....................4-3
4.2 OS(R/T)-3A 118 – 159.4 MHz Analog Board Diagrams...............................4-5
4.2.1 OS(R/T)-3A 118 – 159.4 MHz Analog Board Component Layout (Bottom).....4-5
4.2.2 OS(R/T)-3A 118 – 159.4 MHz Analog Board Component Layout (Top).........4-6
4.2.3 OS(R/T)-3A 118 – 159.4 MHz Analog Board Schematic Diagram ................ 4-7
4.3 OS(R/T)-3H 128 - 174 MHz Analog Board Diagrams..................................4-9
4.3.1 OS(R/T)-3H 128 - 174 MHz Analog Board Component Layout (Bottom)........4-9
4.3.2 OS(R/T)-3H 128 - 174 MHz Analog Board Component Layout (Top)...........4-10
4.3.3 OS(R/T)-3H 128 - 174 MHz Analog Board Schematic Diagram..................4-11
4.4 OS(R/T)-3H 406 - 470 MHz Analog Board Diagrams.................................4-13
4.4.1 OS(R/T)-3H 406 - 470 MHz Analog Board Component Layout (Bottom).......4-13
4.4.2 OS(R/T)-3H 406 - 470 MHz Analog Board Component Layout (Top)...........4-14
4.4.3 OS(R/T)-3H 406 - 470 MHz Analog Board Schematic Diagram..................4-15
4.5 OS(R/T)-3(A/H) Digital Board Diagrams................................................4-17
4.5.1 OS(R/T)-3(A/H) Digital Board Component Layout (Bottom)......................4-17
4.5.2 OS(R/T)-3(A/H) Digital Board Component Layout (Top)..........................4-18
4.5.3 OS(R/T)-3(A/H) Digital Board Schematic Diagram.................................4-19
5 PARTSLISTS.....................................................................................5-1
5.1 OS(R/T)-3H 29 - 71.4 MHz Analog Board Electrical Parts List.......................5-1
5.2 OS(R/T)-3(A/H) 118 – 159.4 MHz Analog Board Electrical Parts List ..............5-5
5.3 OS(R/T)-3H 128 - 174 MHz Analog Board Electrical Parts List......................5-8
5.4 OS(R/T)-3H 406 - 470 MHz Analog Board Electrical Parts List.....................5-11
5.5 OS(R/T)-3(A/H) Digital Board Electrical Parts List ....................................5-14
5.6 OS(R/T)-3(A/H) Synthesizer Mechanical Parts List....................................5-15
6 REVISION HISTORY............................................................................6-1

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Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz 1-1
1 GENERAL
1.1 Introduction
The OS-3A/H Synthesizer Module produces a low distortion, high stability, FM modulated (FM
transmitter) or unmodulated (receiver LO, AM transmitter) RF signal covering the frequency bands
of 29 - 50 MHz, 118 - 159.4 MHz, 118 - 174 MHz and 406 - 470 MHz. It achieves ±1 ppm
frequency stability from -40°C to +60°C with its own internal reference, or it can be slaved to an
external 10/9.6 MHz reference signal of desired stability. The OS-3H Synthesizer Module is
provided in eleven models covering three primary frequency bands (see section 1.2). A synthesizer
module can be easily removed for programming, calibration, or repair. Each synthesizer module
contains two circuit boards providing digital and analog functionality. The analog RF circuitry is
fully isolated in a shielded compartment. Three inter-board filtered wire connections provide signal
and power interface. Digital signal and power control is provided through five photo-logic optical
transceivers, further enhancing electrical noise isolation.
1.2 OS(R/T)-3(A/H) Enhanced Synthesizer Family Models
The OS-3A/H Synthesizer module family forms an integral component of the MT-3 receiver and
transmitter product line. In transmitters, the OS-3A/H synthesizer provides a modulated low level
RF signal to the Power Amplifier module. In receivers, the OS-3A/H synthesizer provides a low
noise local oscillator signal that either directly drives the mixer circuitry or drives a buffer amplifier
in order to achieve higher LO mixer drive required for enhanced intermodulation capability. There
are eleven distinct models in the OS-3H Enhanced Synthesizer Family. Note that this manual
provides service and operating information for all eleven synthesizer family members. It is
important to establish the correct synthesizer model number of interest in order to direct attention to
specific documented information. The specific model number is printed on the synthesizer module
top cover.
The eleven models are described as follows:
Frequency Band: 29 - 50 MHz, Common OS-3H0xx Analog Board
• OST-3H035 - synthesized, installed in transmitter, 29 - 38 MHz RF output.
• OST-3H045 - synthesized, installed in transmitter, 38 - 50 MHz RF output.
• OSR-3H061 - synthesized, installed in receiver, 50.4 - 71.4 MHz RF output.

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1-2 Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz
Frequency Band: 118 - 159.4 MHz, AM Multichannel OS-3H1xx Analog Board
• OST-3A128 - synthesized, installed in AM transmitter, 118 - 138 MHz RF output.
• OSR-3A149 - synthesized, installed in AM receiver, 139.4 - 159.4 MHz RF output.
Frequency Band: 118 - 174 MHz, Common OS-3H1xx Analog Board
• OST-3H141 - synthesized, installed in FM transmitter, 128 – 152.6 MHz RF output.
• OST-3H162 - synthesized, installed in FM transmitter, 150 - 174 MHz RF output.
• OSR-3H141 - synthesized, installed in FM receiver, 128 – 152.6 MHz RF output.
• OSR-3H162 - synthesized, installed in FM receiver, 150 - 174 MHz RF output.
Frequency Band: 406 - 470 MHz, Common OS-3H4xx Analog Board
• OST-3H440 - synthesized, installed in FM transmitter, 406 - 470 MHz RF output.
• OSR-3H440 - synthesized, installed in FM receiver, 427.4 - 451.4 MHz RF output.
The OS-3A/H Enhanced Synthesizer models are very similar; all models use the same digital board
and mechanical construction. The significant differences between the models relate to the analog
board. There are four different analog boards covering the four frequency bands of 29 - 50 MHz,
118 - 159.4 MHz, 128 - 174 MHz and 406 - 470 MHz respectively. Each model’s specific sub
band of operation in a given frequency band is determined by select components on the
corresponding analog board.

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Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz 1-3
1.3 Performance Specifications
Type: NBFM Single loop synthesizer module. Utilizing low noise
VCO and PLL technology. Compatible with Daniels MT-3
series transmitter and receiver modules.
Frequency Range: 29 MHz - 38 MHz [± 0.5 MHz] (OST-3H035)
Tuning range with no adjustment 38 MHz - 50 MHz [± 1.0 MHz] (OST-3H045)
shown in [ ] brackets. 50.4 MHz - 71.4 MHz [± 1.0 MHz] (OSR-3H061)
118 MHz -138 MHz [Full band] (OST-3A128)
128 MHz – 152.6 MHz [± 2.0 MHz] (OST-3H141, OSR-3H141)
139.4 MHz - 159.4 MHz [Full band] (OSR-3A149)
150 MHz - 174 MHz [± 2.0 MHz] (OST-3H162, OSR-3H162)
406 MHz - 470 MHz [Full band] (OST-3H440)
427.4 MHz - 451.4 MHz [Full band] (OSR-3H440)
Output Power: +5 dBm ±2 dBm into 50Ω
Harmonics: <-30 dBc
Spurious: <-90 dBc
<-70 dBc above 400 MHz
Attack Time: <50 ms (Power down mode)
Hum and Noise: -55 dB
Modulation Sensitivity: 3.0 kHz peak deviation / 400 mVrms input
External Reference Input: External reference input signal via SMB connector J1
Input level 0 dBm ± 3 dB.
Input impedance 50Ω
Input frequency 10.0 MHz or 9.6 MHz selected through
digital board jumper JU1.
Power Requirements: +9.5 Vdc @ 160 mA for FM and 65 mA for AM
Standby mode, TCXO enabled:
+9.5 Vdc @ 14 mA for FM and 4 mA for AM

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1-4 Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz
1.4 Printed Circuit Board Numbering Convention
To ease troubleshooting and maintenance procedures, Daniels Electronics Limited has adopted a
printed circuit board (PCB) numbering convention in which the last two digits of the circuit board
number represent the circuit board version. For example:
• PCB number 43-9120 10 indicates circuit board version 1.0;
• PCB number 50002- 02 indicates circuit board version 2.0.
All PCB's manufactured by Daniels Electronics are identified by one of the above conventions.

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Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz 2-1
2 THEORY OF OPERATION
2.1 Internal Power and Control (Digital Board)
Refer to "OS(R/T)-3(A/H) Digital Board Schematic Diagram" in section 4 page 19. The
synthesizer operates from +9.5 Vdc applied to connector pin P1-2. Total current drain is
approximately 160 mA (65 ma for AM). Power Down control (P2-4) controls the +5.0 Vdc
microcontroller regulator U2 through power MOSFET switch U1. For receiver applications, the
synthesizer is always operating with the enable line P2-4 permanently connected to +9.5 Vdc. In
transmitter applications, pin P2-4 is controlled by MT-3 Transmitter Board jumper J18 which
selects the synthesizer's standby mode. In low current standby mode (< 16/4 mA) approximately
50 ms of transmitter turn on delay from PTT activation must be tolerated (lock time of
synthesizer). For transmitter applications requiring less than 10 ms of turn on delay, the
synthesizer can be made to run continuously. This capability comes at the expense of an additional
160 (65 mA for AM) of transmitter standby current.
2.2 Synthesizer Analog Circuitry (Analog Board)
There are four separate analog circuit boards covering the four frequencies bands of 29 - 50 MHz,
118 - 159.4 MHz, 128 - 174 MHz and 406 - 470 MHz respectively. All four analog boards are
similar in operation and circuit topology with the VCO, Loop Filter, and Output Lowpass Filter
sections being band specific. Refer to "OS(R/T)-3(A/H) Analog Board Schematic Diagram” in
section of this manual.
2.2.1 Common Analog Board Circuitry
This section describes the circuitry common to all versions of the FM Synthesizer Analog Board.
The Analog Board utilizes four optical receivers (U1 - U4), and one optical transmitter (U5) to
provide an isolated data interface to the digital board. In normal operating modes, +9.5 Vdc
Regulator IC U8 provides continuous +5.0 Vdc to the internal TCXO and power control optical
receiver U1. This results in a standby current level of ≈10 mA for FM and 4 mA for AM. Primary
power is controlled through activation of optical receiver U1 under control of the digital board
micro controller U4. Regulator U6 provides switched +8.0 Vdc with regulator U7 providing
switched +5.0 Vdc to all analog supply points. Power MOSFET IC U9 works as a clamping
circuit to quickly discharge VCO filter capacitors C32 and C33 when powered down, resulting in
immediate suppression of RF output from the VCO.
The OS-3H enhanced synthesizer is formed around a low power, single chip MC145190
(MC145191) synthesizer IC U10. A 9.6 MHz reference signal is provided from either the internal
TCXO (JU1-B Analog Board), or an external source via SMB connector J1 with jumper JU1-A

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2-2 Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz
(Analog Board) and jumper JU2 (AM Analog Board only) installed. The external reference source
may be 9.6 MHz or 10.0 MHz through selection of jumper JU2 (Digital Board); install jumper
JU2 (Digital Board) for 10.0 MHz reference selection. If an external signal is used for the
reference source, it must be of low phase noise, high stability, with a level of 0 dBm ± 3 dB. A
sinusoidal signal shape is required for an external reference source. A poor quality reference
source will degrade receiver/transmitter performance to unacceptable levels. Transistor Q2 forms a
buffer amplifier having 50Ωinput impedance at 10.0 MHz. The internal 9.6 MHz TCXO provides
better than 1 ppm frequency stability from -30°C to +60°C. Fine frequency adjustment is made
through frequency control potentiometer RV1, which is accessible through the synthesizer top
cover.
The 9.6 MHz reference source is divided down to establish a channel selection step size of
5.0/6.25, 12.5, or 25.0 kHz depending on the particular synthesizer model type. A third order
passive loop filter comprised of C37, C38, C39, C45, C49, R36 and R32, is employed to achieve
the required noise performance, modulation, and worst case switching time of 50 ms. A small
sample of RF energy is coupled from the VCO output buffer U16 on the FM analog board or from
Q6 on the AM analog board to the synthesizer IC U10 prescaler input (pin 11). FM modulation of
the VCO from ≈100 Hz to 3 kHz, is provided through the baseband input pin P1-1 on Digital
Board. A 1 kHz sine wave with a level of approximately 400 mVrms at P1-1 provides FM
deviation of 3.0 kHz. SMB connector J2 provides an RF output level of approximately +5 dBm
into a 50Ωload.
An optional modulation input is provided through connection P1-18 (Digital Board) and routed to
the Analog board via connection P3. This connection must be coupled to a low impedance, dc
coupled source and provides a phase modulated bandwidth from 0 (DC) to ≈50 Hz (PLL loop
filter bandwidth) allowing for specialized applications such as paging or trunking where a separate
low frequency digital/analog modulation channel is required. Phase modulation input pin P1-18 is
routed to the transmitter audio processor spare pin P4-2 via JA4-2 on the MT-3 transmitter main
board. It should be noted that any application of the direct TCXO modulation port transfers the
control of the synthesizer steady state frequency setting to the external modulating source.
Frequency control potentiometer RV1 is effectively removed from the frequency adjust circuitry.
A lock detect LED (LED1) indicates an unlocked PLL condition. An unlocked PLL condition
normally indicates that the VCO is not tuned within the lock in range of the desired channel
frequency. When used in a transmitter, the loss of lock will prevent PTT from keying the power
amplifier module. This prevents transmission of a spurious, unlocked output signal. Adjustment of
tuning capacitor C24 will normally reestablish frequency lock within the synthesizer design
frequency range. Optical transmitter U5 is additionally activated in unlocked conditions and
enables the micro-controller (digital board) to respond to the unlocked PLL state. Note that the
118 – 159.4 MHz and the 406 - 470 MHz Analog Board does not incorporate a VCO tuning
capacitor; the VCO covers the full frequency range without tuning. An unlocked condition in this
case would indicate an attempt to synthesize an invalid channel frequency outside the installed
VCO frequency range.

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Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz 2-3
2.2.2 29 - 71.4 MHz Analog Board Circuitry
Refer to the "OS(R/T)-3H 29 - 71.4 MHz Analog Board Schematic Diagram" located in section 4
page 3 of this manual.
Field effect transistor Q5 provides a VHF negative resistance amplifier/oscillator that is tuned on
frequency by the combination of resonator L5 and a total capacitive reactance presented across L5
through capacitors C62, C63, C64, C23 (Select), variable capacitor C24, and varactor diodes D1
and D2. Fine frequency adjustment is provided by multi-turn trimmer capacitor C24 in conjunction
with coarse frequency jumper selections JU2, JU3, and JU4. Select capacitor values are chosen to
position the operating frequency in one of three bands; 29 - 38 MHz, 38 - 50 MHz, and 50.4 -
71.4 MHz. Varactor diodes D1 and D2 provide oscillator frequency control. PLL voltage feedback
control from the output of the lowpass loop filter controls the VCO frequency through the reverse
biasing of varactor diodes D1 and D2. The PLL control voltage can range from ≈+1.0 Vdc to
+7.0 Vdc and is normally set to ≈+4.5 Vdc for the nominal programmed synthesizer center
frequency. Setting the PLL control voltage set point (TP4) is made by adjusting fine frequency
variable capacitor C24 combined with binary weighted lumped capacitor coarse frequency jumpers
(JU2, JU3, JU4). External baseband frequency modulation is provided through connection P1
and a voltage divider network formed by R21 and R22. A large signal division ratio, established
by the resistive dividers R21 and R22, allows low deviation (less than 5 kHz) direct frequency
modulation of the VCO output signal.
The PLL lowpass filter is formed from select component values C37, C38, C39, C45, R32, and
R36. The loop filter response is optimized for switching time, noise, and modulation requirements
specific to each sub-band within the 29 - 71.4 MHz frequency range. The select component values
(including the loop filter) can be found in tabular format as part of the VHF OS-3H 29 - 71.4 MHz
Analog Board Schematic diagram.
RF output power is taken from the source of Q5 and amplified/buffered by U11. U15 provides
further amplification and isolation while delivering ≈+10 dBm to a six pole lowpass/notch output
filter formed from C53, C57, C58, C59, L11, and L13. The six pole output filter provides a 50
MHz (OST-3H035, OST-3H045 TX) or 80 MHz (OSR-3H061 RX) cutoff frequency which
reduces harmonic output to acceptable levels. SMB connector J2 provides interconnection to the
companion transmitter or receiver with an output level of ≈+5 dBm.
2.2.3 118 - 159.4 MHz Multichannel AM Analog Board Circuitry
Refer to the "OS(R/T)-3H 118 - 159.4 MHz Analog Board Schematic Diagram" located in section
4 page 7 of this manual.
Field effect transistor Q5 provides a VHF negative resistance amplifier/oscillator that is tuned on
frequency by the combination of tapped resonator L5 and a total capacitive reactance presented
across L5 through capacitors C40 and/or C23 (Select), varactor diodes D6, D7, and varactor

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2-4 Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz
diodes D1 and D2. Coarse frequency adjustment is provided by varactor diodes D6, D7. Select
capacitor values C40 or C23 are chosen to position the operating frequency in one of two bands;
118 - 138 MHz, and 139.4 - 159.4.MHz. Varactor diodes D1 and D2 provide fine oscillator
frequency control. PLL voltage feedback control from the output of the lowpass loop filter controls
the VCO frequency through the reverse biasing of diodes D1 and D2. The PLL control voltage can
range from ≈+1.0 Vdc to +4.7 Vdc and is normally set to ≈+3.3 Vdc for the whole range of
synthesizer frequencies. Setting the PLL control voltage set point (TP4) is made by adjusting the
capacitance of varactor diodes D6, D7, which are controlled by a microcontroller U18 through a
digital to analog converter U17. The microcontroller U18 controls the test point TP4, the output of
the PLL Low Pass Filter, and adjusts the output voltage of D/A converter so that the TP4 voltage is
approximately is 3.3Vdc at any frequencies. The microcontroller than goes sleep in order to keep
the power consumption at the low level.
The PLL lowpass filter is formed from select component values C37, C38, C39, C45, R32, and
R36. The loop filter response is optimized for switching time, noise, and modulation requirements
specific to each sub-band within the 118 - 159.4 MHz frequency range. The select component
values (including the loop filter) can be found in tabular format as part of the VHF OS(R/T)-
3(A/H) 118 - 159.4 MHz Analog Board Schematic diagram.
RF output power is taken from the source of Q5 and amplified/buffered by Q6. U11 provides
further amplification and isolation while delivering ≈+10 dBm to a five pole lowpass output filter
formed from C53, C58, C59, L11, and L12. The five pole lowpass output filter provides a 190
MHz low pass cutoff frequency which reduces harmonic output to acceptable levels. SMB
connector J2 provides interconnection to the companion transmitter or receiver with an output level
of ≈+5 dBm.
2.2.4 128 - 174 MHz Analog Board Circuitry
Refer to the "OS(R/T)-3(A/H) 128 - 174 MHz Analog Board Schematic Diagram" located in
section 4 page 11 of this manual.
Field effect transistor Q5 provides a VHF negative resistance amplifier/oscillator that is tuned on
frequency by the combination of tapped resonator L5 and a total capacitive reactance presented
across L5 through capacitors C40 and/or C23 (Select), variable capacitor C24, and varactor diodes
D1 and D2. Fine frequency adjustment is provided by multi-turn trimmer capacitor C24. Select
capacitor values C40 or C23 are chosen to position the operating frequency in one of two bands;
128 – 152.6 MHz and 150 - 174 MHz. Varactor diodes D1 and D2 provide oscillator frequency
control. PLL voltage feedback control from the output of the lowpass loop filter controls the VCO
frequency through the reverse biasing of diodes D1 and D2. The PLL control voltage can range
from ≈+1.0 Vdc to +7.0 Vdc and is normally set to ≈+4.5 Vdc for the nominal programmed
synthesizer center frequency. Setting the PLL control voltage set point (TP4) is made by adjusting
fine frequency variable capacitor C24. External baseband frequency modulation is provided
through connection P1 and a voltage divider network formed by R21 and R22. A large signal

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division ratio, established by the resistive dividers R21 and R22, allows low deviation (less than 5
kHz) direct frequency modulation of the VCO output signal.
The PLL lowpass filter is formed from select component values C37, C38, C39, C45, R32, and
R36. The loop filter response is optimized for switching time, noise, and modulation requirements
specific to each sub-band within the 128 - 174 MHz frequency range. The select component
values (including the loop filter) can be found in tabular format as part of the VHF OS(R/T)-
3(A/H) 128 - 174 MHz Analog Board Schematic diagram.
RF output power is taken from the source of Q5 and amplified/buffered by U11. U15 provides
further amplification and isolation while delivering ≈+10 dBm to a five pole lowpass output filter
formed from C53, C58, C59, L11, and L12. The five pole lowpass output filter provides
a 190 MHz low pass cutoff frequency which reduces harmonic output to acceptable levels. SMB
connector J2 provides interconnection to the companion transmitter or receiver with an output level
of ≈+5 dBm.
2.2.5 406 - 470 MHz Analog Board Circuitry
Refer to the "OS(R/T)-3H 406 - 470 MHz Analog Board Schematic Diagram" located in section 4
page 15 of this manual.
The UHF OS(R/T)-3H 406 - 470 MHz synthesizer employs integrated surface mount VCO
modules (designated U17) for full frequency band coverage. Two VCO modules are used to cover
406 - 470 MHz (TX) and 427.4 - 451.4 MHz (RX) for transmitter and receiver UHF applications
respectively. The receiver VCO module is optimized for low phase noise, while the transmitter
VCO is configured with modulation input capability. PLL voltage feedback control from the output
of the lowpass loop filter controls the VCO frequency through Mod I/P (pin 2). The PLL control
voltage can range from ≈+1.0 Vdc to +7.0 Vdc depending on the selected operating frequency.
External baseband frequency modulation is provided through connection P1 and VCO Mod input
pin 6.
The PLL lowpass filter is formed from select component values C37, C38, C39, C45, R32, and
R36. The loop filter response is optimized for switching time, noise, and modulation requirements
specific to each sub-band within the 406 - 470 MHz frequency range. The select component values
(including the loop filter and VCO type) can be found in tabular format as part of the UHF
OS(R/T)-3H 406 - 470 MHz Analog Board Schematic diagram.
RF output power is taken from the VCO RF output and amplified/buffered by U11. U15 provides
further amplification and isolation while delivering ≈+10 dBm to a five pole lowpass output filter
formed from C53, C58, C59, L11, and L12. The five pole lowpass output filter provides
a 530 MHz low pass cutoff frequency which reduces harmonic output to acceptable levels. SMB
connector J2 provides interconnection to the companion transmitter or receiver with an output level
of ≈+5 dBm.

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2.3 Synthesizer Digital Circuitry (Digital Board)
Refer to the "OS(R/T)-3(A/H) Digital Board Schematic Diagram" on page 4-19. Microcontroller
U4 provides control of the synthesizer module. It communicates with synthesizer IC U10,
monitors the synthesizer lock detect, manages PTT input/output, and determines the operating
frequency from either four rotary BCD switches or four externally driven channel select lines. The
rotary BCD channel switches are located on the main MT-3 Transmitter or Receiver circuit board.
The Microcontroller U4 also communicates with an external factory programmer through I/O lines
TX DATA (P1-17), RX DATA (P1-9), and BOOTSTRAP (P2-2). The external programmer
places the operating program in non volatile microprocessor memory. It is also used to program 15
user defined channel selections. An internal "watchdog" timer provides robust software protection
in all operating modes.
Data communication between the digital and analog circuit boards is provided by four optical
transmitters (U5 through U8) and one optical receiver (U9). The optical interface provides a fully
isolated inter-board data link designed to eliminate digital noise from disturbing sensitive PLL
circuitry.
2.4 Frequency Control
2.4.1 BCD Switch Frequency Control
Selection of the desired synthesizer output frequency is straight forward. If all four of the channel
select lines CHAN SEL3 - CHAN SEL0 are pulled low (grounded), the synthesizer will scan four
BCD switches connected to SW1 COM - SW4 COM and PC4 - PC7 to establish the operating
frequency. The BCD switches are located on the receiver and transmitter main circuit boards.
* Note: The four channel select lines, CHAN SEL3 - Chan SEL0, are connected via the MT-3
transmitter or receiver main board module connector to the M3 motherboard subrack. These lines
may be used for external frequency control. They are normally pulled low via jumper sets located
on the M3 motherboard subrack.
If the channel select lines are pulled high to +9.5 Vdc in any combination resulting in a binary code
greater than 0000 (all low), then the frequency is established as the preprogrammed entry in a table
containing 15 separate frequency settings. For example; if all the channel select lines are pulled
high then a binary code of 1111 results which selects the frequency entry from the 15th table
position. CHAN SEL3 is the most significant bit of the binary channel selection code. The channel
table is normally programmed at the factory for those applications requiring specialized remote
control of frequency. These programmed channel assignments are stored in non-volatile
microprocessor EEPROM and are not susceptible to inadvertent erasure.
In transmitters, the synthesizer operating frequency is the transmitter operating frequency;
however, for receivers, an IF Offset correction factor (21.4 MHz typically) must be added to or

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subtracted from the synthesizer operating frequency in order to determine the actual receive
frequency. Refer to the channel designation table documentation provided with the transmitter or
receiver modules for simplified channel number and frequency information.
2.4.2 Frequency Select Handle Frequency Control
For operation in this mode the external channel select must be set to channel #16. Channel
selection is achieved by pushing the buttons Frequency Increase Øand Frequency Decrease Œon
the Frequency Select Handle. The Frequency Select Handle is located on the Front Panel. The user
interface consists of an 8 digit display and 3 pushbuttons. On power up or key press, the
synthesizer is interrogated for the current channel number and channel frequencies. This
information is used to generate the display, and update the synthesizer itself. The module
communicates with the synthesizer using a standard 2 wire serial interface (9600 Baud, 8 bits, no
parity, 1 stop bit). The command protocols are simple ASCII, both to and from the synthesizer.
The frequency value and the channel are displayed on the Front Panel for several seconds only, in
order to conserve power. Another dedicated line allows the handle to temporarily wake up the
synthesizer if it has been powered down. (This is currently only used on the transmitters)
For the detailed information about changing frequency see the "Frequency Select Handle
Instruction Manual".
2.5 Synthesizer Base and Frequency Increment Table
The OS-3A/H Synthesizer operates in frequency increments of 5.0 / 6.25 kHz, 12.5 kHz, or 25
kHz depending on the particular model and band of operation. The Base Frequency is the lowest
frequency of any given synthesizer model.
Model Number Freq. Range Base Frequency Freq. Increment
OST-3H035 29 - 38 MHz 29 MHz 5.0/6.25 kHz
OST-3H045 38 - 50 MHz 29 MHz 5.0/6.25 kHz
OSR-3H061 50.4 - 71.4 MHz 50.4 MHz 5.0/6.25 kHz
OST-3A128 118 - 138 MHz 118 MHz 25/8.333 kHz
OST-3H141 128 – 152.6 MHz 128 MHz 5.0/6.25 kHz
OST-3H162 150 - 174 MHz 150 MHz 5.0/6.25 kHz
OSR-3H141 128 - 153 MHz 128 MHz 5.0/6.25 kHz
OSR-3A149 139.4 - 159.4 MHz 139.4 MHz 25/8.333 kHz
OSR-3H162 150 - 174 MHz 150 MHz 5.0/6.25 kHz
OST-3H440 406 - 470 MHz 406 MHz 12.5 kHz
OSR-3H440 427.4 - 451.4 MHz 427.4 MHz 12.5 kHz

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2.6 5.0/6.25 kHz Channelization.
The operating frequency is determined as follows for Synthesizers having 5.0/6.25 kHz channel
increment capability;
• for BCD switch settings (in the range of 0000 to 4999, multiply the switch
setting by 5.0 kHz and add it to the synthesizer base frequency.
Example: An OST-3H141 synthesizer has a base frequency of 128 MHz. The
selected channel number is 0988. The synthesizer output frequency is:
((988 x 5 kHz) + 128 MHz) = 132.940 MHz
• for BCD switch settings in the range of 5000 to 9999, subtract 5000 from the
switch setting, multiplying the result by 6.25 kHz and add it to the synthesizer
base frequency.
Example: An OSR-3H162 synthesizer has a base frequency of 150 MHz. The
selected channel number is 7205. The synthesizer output frequency is:
((7205-5000) x 6.25 kHz) + 150 MHz) = 163.78125 MHz
The key point to remember is that 5.0 kHz channel increments are selected with BCD
channel switch settings in the range of #0000 through #4999 and 6.25 kHz channel
increments are selected with BCD switch settings in the range of #5000 through #9999.
2.7 8.333 kHz Channelization.
The operating frequency is determined as follows for Synthesizers having 8.333 kHz channel
increment capability;
• Multiply the BCD switch setting by 8.333 kHz and add it to the synthesizer
base frequency.
Example: An OST-3A128 synthesizer has a base frequency of 118 MHz. The
selected channel number is 0231. The synthesizer output frequency is:
[(1200 x 8.333 kHz) + 118 MHz] = 128.000 MHz

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2.8 12.5 kHz Channelization.
The operating frequency is determined as follows for Synthesizers having 12.5 kHz channel
increment capability;
• Multiply the BCD switch setting by 12.5 kHz and add it to the synthesizer base
frequency.
Example: An OST-3H440 synthesizer has a base frequency of 406 MHz. The
selected channel number is 1978. The synthesizer output frequency is:
((1978 x 12.5 kHz) + 406 MHz) = 430.725 MHz

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3 SYNTHESIZER ALIGNMENT
3.1 General
OS(R/T)-3(A/H) enhanced synthesizer alignment is simplified by using a Type 84 subrack and RF
extender card/cable to provide receiver or transmitter power and signal interconnection.
Alternatively, +9.5 Vdc may be applied directly to a receiver or transmitter module through
positive connection to pins B6 / Z6, and negative connection to pins B30 / Z30 / B32 / Z32.
Receiver balanced audio (600 Ω) is available at pins B26 and Z26.
3.2 Repair Note
The OS(R/T)-3(A/H) synthesizer employs a high percentage of surface mount components which
should not be removed or replaced using an ordinary soldering iron. Removal and replacement of
surface mount components should be performed only with specifically designed surface mount
rework and repair stations complete with Electro Static Dissipative (ESD) protection.
When removing Surface Mount Solder Jumpers, it is recommended to use solder wick braid in
place of vacuum type desoldering tools. This will help prevent damage to the circuit boards.
3.3 Recommended Test Equipment
Alignment of the synthesizer requires the following test equipment or its equivalent.
Power supply - Regulated +9.5 Vdc at 2 A. Phillips PM 2811
Oscilloscope / Multimeter - Fluke 97 Scopemeter
Radio communications test set - Marconi Instruments 2965A
It is recommended that the radio communications test set be frequency locked to an external
reference (WWVH, GPS, Loran C) so that the internal high stability local oscillator may be
accurately set to within its ±1 ppm frequency tolerance.
3.4 OS(R/T)-3(A/H) Synthesizer Factory Configuration
The OS(R/T)-3(A/H) Synthesizer is factory configured as follows:
• Internal 9.6 MHz reference selected.
• VCO modulation by audio processor enabled (OS T TX versions only)

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The corresponding internal synthesizer jumper settings are:
Digital Board
• Jumper JU2 not installed 9.6/10 MHz reference frequency, 9.6 MHz selected
• Jumper JU1 installed AM Multichannel mode selected
Analog Board
• Jumper JU1: 'B' position Internal/External reference. Internal selected
• Jumper JU2 not installed Internal/External reference. Internal selected
3.5 OS(R/T)-3(A/H) Synthesizer Alignment
3.5.1 General
Under normal circumstances, synthesizer alignment is accomplished without removing the
synthesizer from the MT-3 Receiver IF/Audio Board or the MT-3 Transmitter Main Board.
Alignment simply involves setting the internal TCXO reference frequency (if one is installed and
the internal reference option enabled). This step is described in "Reference Frequency Alignment"
of section 3.5.5.5. A change in synthesizer operating frequency greater than the maximum tuning
range for a particular model (Refer to Specifications section 1.3) from an initial factory setting
requires a slightly more involved alignment procedure as described in sections 3.5.2 to 3.5.5. To
convert a synthesizer with an internal reference source to a synthesizer requiring an external
reference signal or vice-versa is done through the appropriate selection of jumper JU1 A or B, and
JU2 (Refer to section 3.5.6).
3.5.2 Synthesizer Test Points
Analog Board Component Layout (Top)
Common to all synthesizer family members.
TP1 +8.0 ± 0.3 Vdc. U6 positive regulator output.
TP2 +5.0 ± 0.1 Vdc. U7 positive regulator output.
TP3 +5.0 ± 0.1 Vdc. U8 positive regulator output (always on).
TP4 PLL error voltage. Ranges from +1.0 to +7.0 Vdc depending on frequency.
Nominally adjusted (C24) to +4.5 Vdc for tuned center channel. UHF/VHF
versions employing integrated VCO modules (OSR-3H440, OST-3H440, OSR-
3A149, OST-3A128) require no adjustment.
Digital Board Component Layout (Bottom)
TP1 +5.0 ± 0.1 Vdc. U2 positive regulator output (controlled via pin P2-4).
TP2 Microcontroller E clock. 2 MHz logic level square wave.