Parts List

Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz 1-1
1. GENERAL
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1.1 Introduction
The OS-3A/H Synthesizer is a compact, fully shielded and environmentally rugged frequency
synthesis module that is the nucleus of every MT-3 synthesized Receiver and Transmitter radio
module. The OS-3A/H generates a high stability, low distortion radio frequency signal in one of
several frequency bands, including 29 - 50 MHz, 118 - 159.4 MHz, 118 - 174 MHz and
406 - 470 MHz. The OS-3A/H utilizes an internal temperature compensated 9.6 MHz reference to
produce a signal stable to ±1 ppm within the temperature range of -40°C to +60°C. Alternately, the
OS-3A/H can be disciplined by an external 9.6 MHz or 10 MHz reference of higher stability. The
OS-3A/H Synthesizer Module is manufactured in twelve distinct model s which cover three primary
frequency bands (see section 1.2 below). All synthesizer modules are designed to be easily
removed for programming, calibration and/or repair. The synthesizer circuitry is distributed
between two printed circuit boards (PCBs) which are isolated yet interconnected via photo-logic
optical transceivers that effectively eliminate residual electrical noise between digital and analog
circuitry. Further shielding of the synthesizer’s RF filter circuitry is provided by an internal
shielded enclosure.
1.2 OS(R/T)-3(A/H) Enhanced Synthesizer Family Models
The OS-3A/H Synthesizer Module is utilized in both the MT-3 Receiver and Transmitter product
lines. In MT-3 Transmitters, the OS-3A/H synthesizer provides a modulated, low-level RF signal
to the Power Amplifier module. In MT-3 Receivers, the OS-3A/H synthesizer provides a low noise
local oscillator (LO) signal that either directly drives the mixer circuitry or first drives a buffer
amplifier which precedes the mixer circuitry (if a higher LO drive signal is required for enhanced
intermodulation capability) . There are twelve distinct models within the OS-3A/H Enhanced
Synthesizer Family . Note that this manual provides service and operating information for all twelve
synthesizer modules. It is extremely important to establish the correct synthesizer model number,
as documentation is model-specific. The model number can be found on the synthesizer label,
located on the synthesizer module top cover.
The twelve synthesizer models that comprise the OS-3A/H Synthesizer family are follows:
Frequency Band: 29 - 50 MHz, Common OS-3H0xx Analog Board
• OST-3H035 - installed in FM transmitter, 29 - 38 MHz RF output.
• OST-3H045 - installed in FM transmitter, 38 - 50 MHz RF output.
• OSR-3H061 - installed in FM receiver, 50.4 - 71.4 MHz RF output.