DE
DANIELS
ELECTRONICS
Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz
2-5
division ratio, established by the resistive dividers R21 and R22, allows low deviation (less than 5
kHz) direct frequency modulation of the VCO output signal.
The PLL lowpass filter is formed from select component values C37, C38, C39, C45, R32, and
R36. The loop filter response is optimized for switching time, noise, and modulation requirements
specific to each sub-band within the 128 - 174 MHz frequency range. The select component
values (including the loop filter) can be found in tabular format as part of the VHF OS(R/T)-
3(A/H) 128 - 174 MHz Analog Board Schematic diagram.
RF output power is taken from the source of Q5 and amplified/buffered by U11. U15 provides
further amplification and isolation while delivering
≈
+10 dBm to a five pole lowpass output filter
formed from C53, C58, C59, L11, and L12. The five pole lowpass output filter provides
a 190 MHz low pass cutoff frequency which reduces harmonic output to acceptable levels. SMB
connector J2 provides interconnection to the companion transmitter or receiver with an output level
of
≈
+5 dBm.
2 . 2 . 5
406 - 470 MHz Analog Board Circuitry
Refer to the "OS(R/T)-3H 406 - 470 MHz Analog Board Schematic Diagram" located in section 4
page 15 of this manual.
The UHF OS(R/T)-3H 406 - 470 MHz synthesizer employs integrated surface mount VCO
modules (designated U17) for full frequency band coverage. Two VCO modules are used to cover
406 - 470 MHz (TX) and 427.4 - 451.4 MHz (RX) for transmitter and receiver UHF applications
respectively. The receiver VCO module is optimized for low phase noise, while the transmitter
VCO is configured with modulation input capability. PLL voltage feedback control from the output
of the lowpass loop filter controls the VCO frequency through Mod I/P (pin 2). The PLL control
voltage can range from
≈
+1.0 Vdc to +7.0 Vdc depending on the selected operating frequency.
External baseband frequency modulation is provided through connection P1 and VCO Mod input
pin 6.
The PLL lowpass filter is formed from select component values C37, C38, C39, C45, R32, and
R36. The loop filter response is optimized for switching time, noise, and modulation requirements
specific to each sub-band within the 406 - 470 MHz frequency range. The select component values
(including the loop filter and VCO type) can be found in tabular format as part of the UHF
OS(R/T)-3H 406 - 470 MHz Analog Board Schematic diagram.
RF output power is taken from the VCO RF output and amplified/buffered by U11. U15 provides
further amplification and isolation while delivering
≈
+10 dBm to a five pole lowpass output filter
formed from C53, C58, C59, L11, and L12. The five pole lowpass output filter provides
a 530 MHz low pass cutoff frequency which reduces harmonic output to acceptable levels. SMB
connector J2 provides interconnection to the companion transmitter or receiver with an output level
of
≈
+5 dBm.
