User's Guide

3-4 Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 935 MHz
The measured RF output signal should be within ±1.0 ppm of the specified oscillator frequency
at an output level of +5 dBm
. Note that unlocked synthesizer operation will be indicated by an
unstable or spurious RF output signal
. The "Unlocked" red LED will also be illuminated when
the PLL is unlocked
. Check that the requested channel number is within the frequency range of
the particular synthesizer model. An unlocked condition may be rectified by adjusting the VCO
tuning elements as described in the following procedures (no adjustment required for the
Multichannel AM Synthesizers). Note that there are variations in alignment procedures between
the three synthesizer family members as described in the following sections.
3.5.5.1 VHF OS(R/T)-3H 29 - 71.4 MHz VCO Alignment
Refer to the
"OS(R/T)-3H 29 - 71.4 MHz Analog Board Component Layout" diagrams and the
"OS(R/T)-3H 29 - 71.4 MHz Analog Board Schematic Diagram" on pages 4-1, 4-2 and 4-3 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
. PLL loop control voltages below approximately +0.5 Vdc and above
approximately +4.5 Vdc will indicate an "out of lock" synthesizer condition.
If a test point (TP4) reading of approximately +2.3 Vdc is unattainable through adjustment of
C24, then the coarse frequency jumpers, JU2-JU4 require modification in order to pull the VCO
tune range within the adjustment range of fine tuning capacitor C24
. The top synthesizer cover
must be removed in order to gain access to the coarse frequency jumpers
. The coarse frequency
jumpers (JU2-JU4) may be considered to be a selectable binary weighted capacitor element with
JU2 being the most significant "bit" and JU4 being the least significant "bit"
. The tuning
resolution size is ≈12 pF (JU4)
. If the tuning voltage remains higher than +2.3 Vdc, decrease the
tuning jumper setting by 1 "bit" position and re-adjust C24 in an attempt to achieve +2.3 Vdc at
TP4
. For example, if coarse frequency jumpers JU2-JU4 are all installed and represented by 111
then a decrease by 1 "bit" position (12 pF) is represented by a binary jumper selection of 110;
jumper JU4 is not installed and jumpers JU2, JU3 are installed
. Continue to decrease the jumper
position one "bit" at a time until the synthesizer regains lock with TP4 adjusted (C24) for
+2.3 Vdc
. If the tuning voltage remains lower than +2.3 Vdc, increase the jumper setting by 1
"bit" position and re-adjust C24 in an attempt to achieve +2.3 Vdc at TP4
. Repeat this procedure
until +2.3 Vdc is achieved at TP4.
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 a +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