User's Guide

Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz 3-5
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 ca pacitor 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.