VHF local oscillator with PLL. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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VHF local oscillator with PLL. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Generators, heterodynes

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Local oscillators with phase locked loop (PLL) allow quite simple means to solve the problem of creating a highly stable variable frequency signal source for sports VHF equipment. A diagram of such a local oscillator is shown in the figure. It was applied in a receiver for the range 144-146 MHz with one frequency conversion and an intermediate frequency of 10,7 MHz.

The local oscillator consists of a controlled oscillator on the transistor V1. a reference quartz oscillator (KG) and a highly stable smooth range oscillator (GPA), a mixer on a transistor V3, a phase detector on diodes V1, V5 and a DC amplifier on an A1 chip. The elements of the quartz and highly stable smooth range generator are not shown in the figure.

The controlled oscillator generates a signal that changes when a control voltage is applied to the varicap V2, within 154,7-156.7 MHz. The signal from this generator is fed to one of the gates of the transistor V3 and through the buffer stage to the first mixer of the receiver. A signal with a frequency of 161 MHz is applied to the second gate of the field-effect transistor from the reference quartz oscillator.

The difference signal, the frequency of which can lie in the range of 4,3-6.3 MHz, is selected on the bandpass filter L5C10C11L6C12. This signal, together with a high-frequency voltage from a smooth range generator, is fed to a phase detector. The error signal, passed through the low-pass filter L7C15 and amplified by the operational amplifier A1, is fed to the varicap V2 in the controlled oscillator.

To expand the bandwidth of the bandpass filter L5C10C11L6C12 up to 2 MHz, its circuits are shunted by resistors R9 and R12.

The frequency stability of the output signal of the local oscillator with a PLL is determined mainly by the stability of the smooth range generator, which at low frequencies (in this case 4,3-6.3 MHz) can be obtained very high.

Note

Transistor V1 can be any high-frequency transistor with a maximum generation frequency of at least 300 MHz (for example, KT603A). Transistor V3 - field series KP306 or KP350A, varicap V2 - series KB 102. Diodes V4 and V5 - any high-frequency, for example, series D9. As an operational amplifier, you can use K153UD1A with the appropriate correction circuits. The phase detector transformer can be wound on a ferrite ring with a diameter of 7-10 mm with a permeability of 400-1000 simultaneously with four wires (20 turns). Two windings connected in series form the primary winding of the transformer (the common connection point of the windings is not used), and the other two form the secondary.

The winding data of the inductors L1-L3 and the inductor L4 depend on the frequency range in which the controlled generator must operate, i.e. on the choice of the first intermediate frequency and the tuning range of the GPA.

Literature

"Radio communication" (Great Britain). 1976, N12

Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Knots of amateur radio equipment. Generators, heterodynes.

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