Microwave generator with PLL: prefix to the RF generator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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Specialized microassemblies of self-oscillators, used in conjunction with a frequency synthesizer, greatly simplify the manufacture of a measuring oscillator in the microwave range. The author proposed the design of a set-top box - a oscillator with a PLL for the ranges of 0,66 ... 1,53 and 1,71 ... 2,75 GHz, for which an external highly stable signal generator with a frequency of not more than a few megahertz is used as a model.

Carrying out repair and adjustment work of equipment and antennas in the range of 300 MHz and higher is often difficult due to the lack of measuring equipment, in particular generators. The way out of this situation can be to manufacture a microwave generator on your own. Descriptions of the designs of such generators for one or more fixed frequencies can be found in the journal "Radio" [1, 2]. The principle of operation of these generators is based on the use of a phase locked loop (PLL), but their capabilities are limited due to the lack of smooth frequency tuning. The use of such a generator will expand if it is made in the form of a prefix to the RF generator [3]. In this case, the RF generator will perform the functions of a reference frequency generator and, by changing its frequency, it is possible to control the frequency of the microwave generator.

The attention of readers is offered a description of the microwave generator - attachments to the RF generator, its circuit is shown in fig. 1. Potentially, it can operate in the frequency range of 0,1 ... 4 GHz, but with the details indicated in the diagram, it covers the ranges of 0,66 ... 1,53 and 1,71 ... 2,75 GHz allocated for cellular and amateur radio communications.

Rice. 1 Schematic diagram of the device

The set-top box is built on the basis of a specialized DA4 frequency synthesizer microcircuit, which contains the main components: two frequency dividers with a variable division ratio (CVD) and a frequency-phase detector (FPD). The modes of its operation are controlled by the microcontroller DD1. Specialized microassemblies of DA5 and DA6 self-oscillators with electronic frequency tuning were used as microwave generators. The supply voltage of the nodes is stabilized by integrated voltage regulators DA2 (12 V) and DA3 (5 V). An external RF generator was used as a reference frequency signal source. Since its frequency does not exceed a few megahertz, for the normal operation of the synthesizer microcircuit, the external generator signal is converted into a rectangular shape by the DA1 comparator.

An additional stage is assembled on the transistor VT1, which, together with the elements R8, R9, C13, C15, C19, performs the functions of a proportionally integrating filter and is also needed in order to increase the maximum value of the control voltage to 12 V. The frequency subrange is selected by the SA1 switch by supplying supply voltage to the corresponding oscillator. An attenuator with a total fixed attenuation of 15 dB is assembled on resistors R18-R60. If the PLL is working properly, then the HL1 LED will light up.

The microwave generator has two outputs: main (XW2) with a signal level of 0 dBm (voltage - 226 mV at a load of 50 ohms, which corresponds to a power of 1 mW) and additional (XW3) with a level of -60 dBm. Smooth adjustment of the output signal is made by an external stepped attenuator in the range of 0-70 dB in 1 dB steps - from an industrial measuring device X1-42, X1-43 or similar. When using the second output (XW3), the first one (XW2) must be terminated (50 Ohm).

The device operates in such a way that it adjusts the frequency of the microwave generator to a multiple of the frequency of the external generator. In this case, the operating mode of the DA4 microcircuit is set in such a way that the DPKD division factor for the microwave generator signal is 1000, and for the external generator signal it is 1. Thus, the CFD operates at the frequency of the external generator and each hertz of the external generator frequency will correspond to 1 kHz of the microwave generator , it simplifies frequency setting. It should be noted that in this case the frequency stability and phase noise depend mainly on the signal quality of the external generator. If you apply other microassemblies of oscillators, you can get other frequency subranges within the above limits. And if you use the ADF4106 chip, then the upper frequency of the device can be increased to 6 GHz.

The board is placed in a metal case with a closed cover. The output socket XW3 with resistors R17, R18 is installed in a separate compartment, and the supply voltage is supplied through a separate compartment and a feed-through capacitor. Parallel to the input of the set-top box, capacitor C6 is connected, which reduces the penetration of the microwave generator signal to the outside.

The following parts can be used in the device: transistor KT3130 with any letter indices, tuned resistors - PVZ3A and similar, the rest - P1-12 (size 1206), non-polar capacitors - ceramic K10-17 (C1 - KTP-1), C2, C7, C10 - tantalum or other oxide-semiconductor, suitable for surface mounting. Inductors L1-L3 - CM453232 for surface mounting with an inductance of 20 ... 200 μH. You can install any LED, preferably high brightness. RF jacks - block SMA or similar. The switch - any small-sized on two positions and two directions. It is necessary to "sew" the program below into the microcontroller.

:10000000160A2800080C27000304680303060A0ADE
:1000100026040B0A26050605000000000604E70278
:10002000040A0008460500004604000840000600D7
:100030001F0C02006600030C0109B00C0109120C30
:1000400001091209000С0109000С0109040С010945
:100050001209000C01097D0C0109010C01091209AA
:10006000030С0109В00С0109120С0109120903006В
:02lFFE00EA0FE8
:00000001FF

Most of the parts are placed on a printed circuit board made of double-sided foil fiberglass 1,5 mm thick, a sketch of which is shown in Fig. 2. The second side is left metallized and connected to the metallization of the other side with foil along the board contour. In addition, both are connected by pieces of wire and through holes in the board. The appearance of the console is shown in fig. 3.

Rice. 2 PCB sketch

Establishment comes down to setting resistors R8, R9 stable operation of the PLL with minimal phase noise over the entire frequency range of the generator. The output signal power is set first at socket XW2 by resistors R12, R14, and then by resistors R15, R16 at socket XW3. To power the device, you can use a stabilized power supply with a voltage of 13 ... 15 V or an unstabilized voltage of 15 ... 20 V, the current consumption is 65 ... 80 mA.

Rice. 3 Appearance of the console

Literature:

1. Malygin I., Shturkin N. Laboratory microwave synthesizer. - Radio, 2004, No. 1, p. 19, 20.
2. Nechaev I. UHF heterodyne. - Radio, 2005, No. 8, p. 69, 70.
3. Nechaev I. PLL oscillator for VHF-UHF bands. - Radio, 2004, No. 12, p. 33,34.

Author: I. Nechaev, Kursk; Publication: radioradar.net

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