User's Guide

3-6 Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz
3.5.5.4 UHF OS(R/T)-3H 406 - 470 MHz VCO Alignment
Refer to the "OS(R/T)-3H 406 - 470 MHz Analog Board Component Layout" diagram and the
"OS(R/T)-3H 406 - 470 MHz Analog Board Schematic Diagram" on pages 4-13, 4-14 and 4-15 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 . The UHF synthesizers operating in the 406 - 470 MHz frequency range employ
integrated VCO modules having no external frequency adjustment capability . The OST-3H418,
OST-3H460 and OSR-3H440 models co ver frequencies from 406 - 430 MHz, 450 - 470 MHz and
427.4 - 451.4 MHz respectively and provide full band coverage without tuning adjustment . For the
OST-3H418, measured PLL control voltages below approximately +0.5 Vdc and above
approximately +4.5 Vdc w ill indicate an “out of lock” condition. For the OSR-3H440 and the
OST-3H460, measured PLL control voltages below approximately +1.0 Vdc and above
approximately +7.0 Vdc will indicate an “out of lock” 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 +0.5 to
+4.5 Vdc range for the OST-3H418. The TP4 voltage for the OSR-3H440 and the OST-3H460
should be within the +1 .0 to +7.0 Vdc range. 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.
3.5.5.5 Reference Frequency Alignment
Adjust the synthesizer TCXO fine frequency potentiometer RV1 until the correct output frequency
is achieved . Access to this potentiometer is through an opening in the synthesizer top cover . A RF
power level of approximately +5 dBm should be measured at the synthesizer module output
connector and the frequency should be within ±1 ppm of the desired operating frequency.
Reference frequency adjustments should be made at room temperature (+25°C) after a ten minute
stabilization period.