User's Guide

Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 935 MHz 1-1
1 GENERAL
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,
406 - 470 MHz and 928 – 935 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 thirteen
distinct models which cover five 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 thirteen distinct models within the OS-3A/H
Enhanced Synthesizer Family
. Note that this manual provides service and operating information
for all
thirteen 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 thirteen 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.