User's Guide

Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 935 MHz 3-5
synthesizer will result in unlocked operation. The tuning range capability of all synthesizer
models is listed in the Specifications section (1.3) of this manual.
3.5.5.2 VHF OS(R/T)-3A 118 - 159.4 MHz Alignment
Refer to the
"OS(R/T)-3A 118 - 159.4 MHz Analog Board Component Layout" diagram and the
"OS(R/T)-3A 118 - 159.4 MHz Analog Board Schematic Diagram" on pages 4-5, 4-6 and 4-7 of
this manual.
Using a high impedance (10 MΩ) DC Voltmeter, measure the PLL control voltage at TP4
located on the synthesizer module analog board (top)
. Access to TP4 is available through the
synthesizer top cover
. VHF synthesizers operating in the 118 - 159.4 MHz frequency range
require no frequency adjustment as tuning is microprocessor controlled. (The OST-3A128 and
OSR-3A149, covering 118-138 MHz and 139.4 - 159.4 MHz respectively, provide full band
coverage without tuning adjustment.)
All channel selections should result in a TP4 voltage between +3.1 and +3.5 Vdc. Channel
selections beyond the tuning range capability of the synthesizer will result in unlocked operation
over the temperature range -40C to +60C
. The tuning range capability of all synthesizer models
is listed in the Specifications section of this manual.
3.5.5.3 VHF OS(R/T)-3H 128 - 174 MHz VCO Alignment
Refer to the
"OS(R/T)-3H 128 - 174 MHz Analog Board Component Layout" diagram and the
"OS(R/T)-3H 128 - 174 MHz Analog Board Schematic Diagram" on pages 4-9, 4-10 and 4-11 of
this manual.
Using a high impedance (10 MΩ) DC Voltmeter, measure the PLL control voltage at TP4
located on the synthesizer module analog board (top). Access to TP4 is available through the
synthesizer top cover. Using a small standard blade screwdriver, carefully adjust the VCO fine
frequency "TUNE" trimmer capacitor C24 until a test point (TP4) voltage of approximately
+2.3 Vdc is obtained. Measured PLL loop control voltages below approximately +0.5 Vdc and
above approximately +4.5 Vdc will indicate an "out of lock" synthesizer condition.
It is important to check the loop control voltage at TP4 when multiple synthesizer channels have
been programmed. All channel selections should result in a TP4 voltage within the +1.0 to
+4.0 Vdc range. Adjust the fine-tuning capacitor C24 to center multiple channel voltages
symmetrically about +2.3 Vdc. Channel selections beyond the tuning range capability of the
synthesizer will result in unlocked operation. The tuning range capability of all synthesizer
models is listed in the Specifications section of this manual.