Daniels Electronics Ltd. OST-3H035 Instruction Manual
Also see for MT-3: Instruction manualInstruction manualInstruction manual
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DE DANIELSELECTRONICS2-4 Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHzdiodes D1 and D2. Coarse frequency adjustment is provided by varactor diodes D6, D7. Selectcapacitor values C40 or C23 are chosen to position the operating frequency in one of two bands;118 - 138 MHz, and 139.4 - 159.4.MHz. Varactor diodes D1 and D2 provide fine oscillatorfrequency control. PLL voltage feedback control from the output of the lowpass loop filter controlsthe VCO frequency through the reverse biasing of diodes D1 and D2. The PLL control voltage canrange from ≈ +1.0 Vdc to +4.7 Vdc and is normally set to ≈ +3.3 Vdc for the whole range ofsynthesizer frequencies. Setting the PLL control voltage set point (TP4) is made by adjusting thecapacitance of varactor diodes D6, D7, which are controlled by a microcontroller U18 through adigital to analog converter U17. The microcontroller U18 controls the test point TP4, the output ofthe PLL Low Pass Filter, and adjusts the output voltage of D/A converter so that the TP4 voltage isapproximately is 3.3Vdc at any frequencies. The microcontroller than goes sleep in order to keepthe power consumption at the low level.The PLL lowpass filter is formed from select component values C37, C38, C39, C45, R32, andR36. The loop filter response is optimized for switching time, noise, and modulation requirementsspecific to each sub-band within the 118 - 159.4 MHz frequency range. The select componentvalues (including the loop filter) can be found in tabular format as part of the VHF OS(R/T)-3(A/H) 118 - 159.4 MHz Analog Board Schematic diagram.RF output power is taken from the source of Q5 and amplified/buffered by Q6. U11 providesfurther amplification and isolation while delivering ≈ +10 dBm to a five pole lowpass output filterformed from C53, C58, C59, L11, and L12. The five pole lowpass output filter provides a 190MHz low pass cutoff frequency which reduces harmonic output to acceptable levels. SMBconnector J2 provides interconnection to the companion transmitter or receiver with an output levelof ≈ +5 dBm.2.2.4 128 - 174 MHz Analog Board CircuitryRefer to the "OS(R/T)-3(A/H) 128 - 174 MHz Analog Board Schematic Diagram" located insection 4 page 11 of this manual.Field effect transistor Q5 provides a VHF negative resistance amplifier/oscillator that is tuned onfrequency by the combination of tapped resonator L5 and a total capacitive reactance presentedacross L5 through capacitors C40 and/or C23 (Select), variable capacitor C24, and varactor diodesD1 and D2. Fine frequency adjustment is provided by multi-turn trimmer capacitor C24. Selectcapacitor values C40 or C23 are chosen to position the operating frequency in one of two bands;128 – 152.6 MHz and 150 - 174 MHz. Varactor diodes D1 and D2 provide oscillator frequencycontrol. PLL voltage feedback control from the output of the lowpass loop filter controls the VCOfrequency through the reverse biasing of diodes D1 and D2. The PLL control voltage can rangefrom ≈ +1.0 Vdc to +7.0 Vdc and is normally set to ≈ +4.5 Vdc for the nominal programmedsynthesizer center frequency. Setting the PLL control voltage set point (TP4) is made by adjustingfine frequency variable capacitor C24. External baseband frequency modulation is providedthrough connection P1 and a voltage divider network formed by R21 and R22. A large signal |
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