Parts List

Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz 2-5
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 low-pass filter is formed by SELECT components 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 components
(including the loop filter) can be found in tabular format on 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 ampli fication and iso lation while delivering ≈ +10 dBm into a five pole low-pass output
filter formed by C53, C58, C59, L11 and L12. The five-pole low-pass output filter, with a cutoff
frequency of 190 MHz, effectively eliminates output harmonics. 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" on page 4-15 of this
manual.
The UHF OS(R/T)-3H 406 - 470 MHz synthesizer employs an integrated surface mount VCO
module (U17) capable of full frequency band coverage. Two VCO modules are used to cover the
406 - 470 MHz frequencies in the Transmitter module and the 427.4 - 451.4 MHz frequencies in
the Receiver module. The VCO modules are optimized for low phase noise, however the transmitter
VCO is additionally configured with modulation input capability. PLL feedback control voltage, at
the output of the low-pass loop filter, controls the VCO frequency through pin 2;the modulation
input (Mod I/P) port. The PLL control voltage can range between ≈ +1.0 Vdc and +7.0 Vdc
depending on the selected operating frequency. External baseband frequency modulation is
provided through connector P1 and VCO Mod input pin 6.
The PLL low-pass filter is formed by SELECT components 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 components
(including the loop filter and VCO type) can be found in tabular format on 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/b uffered by U11. U15 provides
further amplification and isolation while delivering ≈ +10 dBm to a five pole low-pass output filter
formed by C53, C58, C59, L11 and L12. The five-pole low-pass output filter, with a cutoff
frequency of 530 MHz, effectively eliminates output harmonics. SMB connector J2 provides
interconnection to the companion transmitter or receiver with an output level of ≈ +5 dBm.