Vaclav Papez

Power wire-wound RF resistor with high linearity

This paper describes a wire resistor with the resistance of several hundreds ohms, with a power dissipation up to several hundreds watts. In a high frequency band, it shows maximum frequency reflection coefficient values with respect to the nominal resistance value of about 0.1, and which reaches a third order IM distortion products close to −130dBc at the dissipation power.

Highly pure signal generators

The special testing signal generators were designed for a series of frequencies in the frequency band 0.5 to 20 MHz. The generator is very simple. It is composed of only one stable crystal oscillator and one high power amplifier. The frequency stability of the generators is in the order of 10−6/day, the output power is 1W, the value of SINAD is under −130 dB and the total harmonic distortion is under −170 dB by using a linear narrowband filter.

Equipment for measurement of nonlinearity of nominally linear components

Nonlinearity of a nominally linear component is a significant parameter, which informs about the difference of and investigated component from an ideal one. The higher is quality of the nominally linear component; the lower is level of its nonlinearity. Nonlinearity is caused by inhomogenities and unstable barriers in the component, which can, after some time, cause failure of the component. Nonlinearity is also a significant technical parameter of components, which work with more signals of different levels. Nonlinearity contributes here to generation of intermodulation distortion of current signals. It has been necessary, for our research, to investigate nonlinearity of adhesive joints. Because there is not equipment for measurement of nonlinearity of low-impedance components on the market, it has been necessary to construct it. Equipment is based on evaluation of intermodulation distortion, which is generated by the nonlinear component, when two sinusoidal signals are fed into it. Equipment makes a measurement of nonlinearity of 2. to 5. order possible. Measured level of nonlinearity is -170 dB with respect to the actuating signal. Maximum power of the actuating signal is 2 VA, the sensitivity of an indicator 50 nV. Some examples of measurements of nonlinearity of adhesive joints are shown.

Frequency Dependence of Impedance of Adhesive Joints

Electrically conductive adhesives have, in comparison with solders, significantly higher non-homogeneity of the structure, and therefore stability of electrical as well as mechanical properties of adhesive joints is lower than soldered ones. The impedance of the joints has been measured in wide frequency range (20 Hz to 1 MHz and 300 MHz to 3GHz). Measurements have been carried out by two methods: impedance in the range 20 Hz to 1MHz has been measured by LCR meter HP 4284A. A special test board for assembly of 1 jumper (of the type 1206) by electrically conductive adhesive has been fabricated for this measurement. The measurements at the frequencies 300 MHz and higher have been carried out using a shielded high-Q triplate line. Specimens have been prepared on Teflon boards, a scalar analyzer Rohde Scwartz ESPI has been used for evaluation. Very low changes of impedances of the joints have been found in the range of 20 Hz to 1 MHz. Typical courses of real and imaginary components of joints impedances in the frequency range 300 MHz to 3 GHz are as follows: the real components have grown in consequence of a skin-effect and have dominated. The imaginary components have been very low. The task for the future research is to explain decrease of the resistance of the joints with growing frequency for two types of adhesives

Target position determining in aeronautical issues

This article discusses the possibilities of the location of aircraft via active and passive radiolocation systems. The next part is dedicated to location recording of the aircraft, which uses the general type of Radiolocation Warning Receiver by triangulation method and PG method. Then we examine the analysis of the measured data with the purpose of determination of the location of source radiotechnical signal, using the general calculation algorithm and map image. Finally, we check the relevance of the results via graphical analysis, which was based on line of sight and special software computing.

Non-linearity diagnostics of nominally linear components

Traditional methods and new method for measurement of low non-linearity of electronic components and circuits are described in this paper. Maintaining a linearity of components and circuits that are on principle linear is a measure of their quality. Passive intermodulation distortion (PIM) and non-linearity itself arises as a result of faults in production or component degradation and limits their usability.

Transformer short-time overload testing

An increased level of safety in operation is one of the requirements prescribed by EU regulations for control trans-formers. This requirement is verified by a special test of the transformer resistance during its short-time overload. The paper provides an analysis of testing conditions and gives an example of the testing equipment construction.

High sensitivity phase noise measuring equipment

This article describes a device for a phase noise measurement using the phase locked loop (PLL). This allows measuring signals with the possibility of passing the phase noise better than -160 dB. There are analyzed the effects of the measuring device on the measuring results and presented examples of solving the PLL, circuits for low-frequency signal processing and power supplies with their minimal basic noise.

Equipment for the automatic testing of power capacitors

The paper describes a special method for testing power capacitors by means of their loading by alternating current with the effective value up to 100 A at frequencies in the order of units up to tens of kHz. There is described the realization of the test equipment enabling a precise compensation of the reactive power of the capacitor and the input minimisation at the testing. It discusses the realization of the key components and parts of the measuring equipment.

Influence of surface states on the reverse and noise properties of silicon power diodes

This contribution investigates transient degradation of reverse characteristics of diodes by means of a noise measurement. This effect appears immediately after external heating or after a long time on-state polarisation of diodes (without a significant temperature growth of the device in this case). Simultaneously with the reverse characteristics degradation, the noise power measured under a low voltage DC reverse bias is influenced. The first possible cause of these effects is connected with so called slow surface states (SSS). The SSS are caused by the presence of material process induced defects in the region of a p-n junction surface termination. SSS have fundamental impact on the reverse properties of diodes and their low frequency noise behaviour. The second cause is connected with so called volume structural defects (VSD). Their origin can be ‘genetic’ (e.g. the presence of imperfection inside a silicon crystal) or they can be induced during technological processing. These defects are not repairable and under the reverse bias they will form so called ‘hot spots’ that is, places with a local high current density. Rapid and operative measurements of the noise power can reveal latent instabilities of reverse characteristics invisible during a standard inspection process during the production.