Impedance matching is a fundamental task in any EM design or RF/wireless design and implementation. Many a circuit has failed to work satisfactorily because of improper impedance matching.
A book published by Signal Processing Group Inc. and authored by Ain Rehman is now available from Amazon. It deals with quantities such as reflection coefficients, return loss, VSWR, Smith Chart use for impedance matching etc. A set of calculators is also available as shown below.
The feed point impedance of a half wave dipole antenna is best calculated using computer programs such as NEC2/4.1. However, a theoretical expression for the feed point impedance of a half wave dipole, remote from everything else , made of an infinitely thin conductor is 73 + j42.5 Ohms. for reference. This impedance is affected by the wavelength to diameter ratio of the conductors.used for the dipole. It is assumed that the signal source is directly at the antenna feed point. Please contact Signal Processing Group Inc., with further information on the modeling and simulation of antennas using NEC2/4 or FEKO
The process of impedance matching in electronic circuits is an important one. Thee are several accepted ways of do this and many of these techniques have been implemented in circuit simulators. However, failing the access to an advanced circuit simulator, javascript based calculators are a useful aid to the process of understanding reflection coefficients, return loss, VSWR, Smith Charts, transmission lines, etc. Signal Processing Group Inc., has released a set of calculators available online for interested users. These calculators are part of a recent book on VSWR and impedance matching but can be accessed independently of the book itself. Please access the calculators at http://www.signalpro.biz/impmatch.html.
A recent book published by Signal Processing Group Inc., and authored by Ain Rehman is now available for purchase at Amazon. The idea behind the book is the “eCADBook” (TM). The book deals with fairly important quantities in topics such as VSWR, reflection coefficients, return loss, mismatch loss, s11/s22, impedance matching, the use of Smith charts in impedance matching, transmission lines etc. The mathematics is kept to a minimum in the text with emphasis being placed on intuitive understanding. However, the “Math” is not entirely forgotten and is embodied in a set of Javascripts ( provided separately). The reader can use these scripts to calculate results quickly without getting lost in a morass of mathematical expressions.
A very simple and reliable oscillator can be made using the CD4093 CMOS Schmitt trigger. It will oscillate easily and can reach very low ( mHz or lower) frequencies. Higher frequencies are somewhat limited owing to the limitations of the CD4000 series logic. Nonetheless, this oscillator is truly a very useful circuit to know and can be put together very quickly. Supply voltages of 5.0V to 18V can be used. Signal Processing Group Inc.has recently released a simple EXCEL spreadsheet that can be used to calculate the frequency of this oscillator given the resistance, capacitance and the Schmitt thresholds. Interested readers can access this spreadsheet from the “Free items…” part of the SPG website
Power spectral density is an important parameter used in signal processing. When a signal is deterministic a number of well known tools such as the Fourier transform can be used easily to look at frequency domain behavior etc. However, if the signal is random how does one go about analyzing it? One of the tools used to analyze random signals is the power spectral density. This quantity does not lend itself to immediately intuitive understanding, and in spite of a significant number of papers written on it, its actual essence can be missed. A new tutorial has been released by Signal Processing Group Inc., whose intent is to try and explain in a more heuristic sense what the PSD, as well as some related terms is. This paper may be accessed from the SPG website under free items for interested readers..
