Microwave laboratory synthesizer. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Microwave laboratory synthesizer. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Measuring technology

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When developing and setting up microwave devices, radio amateurs often face difficulties associated with the lack of measuring equipment of the required frequency range. The proposed frequency synthesizer can be made in amateur conditions. It operates in the range of 1900...2275 MHz. The frequency value is selected from several possible ones using a switch.

At relatively low frequencies (up to 100 ... 150 MHz), the problem of stabilizing the frequency of the generator is solved by using quartz resonators, at higher frequencies (400 MHz) - using surface acoustic wave resonators (SAW resonators), for microwaves use dielectric resonators made of high-quality ceramics and other high-quality resonators. Stabilization with the help of passive components has its advantages - simplicity and relatively low cost of implementation. Its main disadvantage is the impossibility of a significant change in the frequency of the generated signal without changing the frequency setting element.

Widespread integrated frequency synthesizers make it possible to implement fast electronic tuning of the oscillator (including microwave), while maintaining high frequency stability. Synthesizers come in direct and indirect types.

The advantages of direct synthesis are considered to be a high frequency change rate and tuning with a small step. However, due to the presence in the synthesized signal of a large number of spectral components resulting from numerous nonlinear transformations, direct synthesis devices are rarely used in microwave equipment.

(click to enlarge)

For microwave synthesis, indirect-type synthesizers with phase-locked loops (PLL) are more often used. The principle of PLL operation, as well as the method for calculating the feedback filter, are widely and repeatedly considered in the literature, for example, in [1]. There are several freeware programs that allow you to calculate the optimal parameters of feedback filters, they can be found on the Internet at the site or .

Integrated PLL synthesizers are of two types: programmable (frequency values are set by external commands) and non-programmable (fixed multiplication and division coefficients of the reference frequency cannot be changed).

The disadvantages of non-programmable integrated synthesizers, for example, MC12179, include the need to use a quartz resonator with a precisely specified frequency, which is not always possible. Programmable synthesizers such as the UMA1020M do not have this disadvantage. In the presence of a control microcontroller, it is technically easy to tune such a synthesizer to a given frequency. Microwave oscillators with electronic frequency tunability required for joint work with a synthesizer microcircuit are available to the consumer in the form of functionally complete modules made using hybrid technology [2].

(click to enlarge)

A diagram of a laboratory frequency synthesizer designed to check and adjust the tuning of 2 GHz band equipment is shown in Fig. 1. Its basis is the UMA-1020M (DA3) chip, the technical documentation for which can be found on the manufacturer's website at .

Microwave laboratory synthesizer

The synthesizer also has a voltage-controlled oscillator (VCO) DA1, a crystal oscillator of a reference frequency of 10 MHz DA2 and a microcontroller DD1. The microwave signal from the output of the VCO is fed to the output of the synthesizer (connector XW1) and to the input of the main programmable frequency divider of the DA3 microcircuit. The reference frequency signal from the output of the DA2 generator is fed to an auxiliary programmable frequency divider, which is also part of the DA3 chip.

The frequency division ratios of the main and auxiliary dividers are set by the DD1 microcontroller (Z86E0208PSC), sending the corresponding commands via the three-wire information bus (pins 11-13 DA3). The source text of the control program is given in Table. 1. The internal memory of the microcontroller is sufficient to store data on seven different frequency values. One of the frequency values or the mode in which there is no output signal is selected by jumpers S1-S3 according to table. 2. The set mode takes effect at the moment the device is turned on, after which no manipulations with the switches affect its operation until the device is turned on again. The HL1 LED should go out 1 s after the power is turned on. You can read about programming microcontrollers from Zilog in [3].

Microwave laboratory synthesizer

The synthesizer is assembled on a printed circuit board, the appearance of which is shown in fig. 2. Resistors and capacitors for surface mounting are applied.

Literature

Starikov O. PLL method and principles of synthesizing high-frequency signals. - Chip News, 2001, No. 6.
VCO Designer's Handbook 2001. VCO/HB-01. - Mini Circuits.
Glvdshtein M. A. Microcontrollers of the Z86 family from Zilog. Programmer's Guide. - M.: DODEKA, 1999, 96 p.

In addition to the microwave synthesizer, the UMA1020M chip contains another one operating in the frequency range of 20..300 MHz. 6n is not used in the described design.

Authors: I. Malygin, N. Shturkin, Yekaterinburg

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