An antenna is simply a conductor or conductor array, usually metal. But how it is situated and terminated that determines its behavior in transmitting and/or receiving electromagnetic radiation. Let’s start with an antenna that is configured to transmit. An oscillating voltage applied at a terminal will cause current to flow through the antenna. A transmitting […]
FAQ
Cathode ray tube testing using an oscilloscope
The cathode ray tube (CRT) is what made possible TVs, computer monitors, and oscilloscopes as we know them. CRTs have largely been replaced by flat-screen technologies but CRTs still serve in niche applications. For example, some kinds of military needs still require a CRT display. General-purpose CRTs are no longer manufactured in the U.S., but […]
Measuring active and passive filters
The usual rationale for a filter in electronic circuitry is to reject unwanted portions of a spectrum or at least reduce their amplitudes to acceptable levels without attenuating the desired frequency or range of frequencies. In some situations, active filters are needed to perform this function, and often they are less expensive than alternate solutions […]
Measuring Ebers-Moll model parameters in transistors
If transistor circuits are to be of any use or amenable to diagnostic procedures, we must be able to model them. Even the best electronic test equipment is useless if we don’t know what to look for in the circuits under investigation. Transistors characteristically have multiple modes of conduction. We can view these phenomena in […]
Measuring emitter followers and other transistor configurations
There are three bipolar junction transistor amplifier topologies: common emitter, common base and common collector. (For field-effect transistors, the analogous circuit configurations are common source, common gate and common drain. In the old world of vacuum tubes, they were common cathode, common grid and common plate.) This particular classification derives from the external circuit configuration. […]
Thevenin and Norton help interpret measurement results
Engineers are often tasked with making sense of what initially looks like a tangle of wires, electrical energy sources, and components. Before attacking such situations with scope probes, it’s good to recall a few basics. Thévenin’s Theorem states it is possible to simplify any linear circuit to a single equivalent circuit composed of a single […]
Dealing with and displaying power-line harmonics
Harmonics are waveforms that may accompany a periodic fundamental (also known as the first harmonic) in a divergent infinite series. When they arise, their frequencies are integer multiples of the fundamental. If this fundamental is 60 Hz, the second harmonic is 120 Hz, the third harmonic is 180 Hz, the fourth harmonic is 240 Hz […]
Testing operational amplifiers
Because it is able to function in so many diverse ways, the op-amp can be the defining element in electronic circuits of any complexity. Applications go far beyond amplification. Because they are near-perfect dc amplifiers, op-amps are suitable for filtering, signal conditioning, and for performing such mathematical operations as addition, subtraction, differentiation, and integration. Op […]
Test gear for wireless communication systems
Various types of wireless communications systems are characterized by the distances that they can travel. Short distances are conveniently spanned using Bluetooth technology, occupying the radio frequency spectrum from 2.4 to 2.485 GHz. Bluetooth was originally developed to replace RS-232 cabling and it is used to link fixed and mobile devices. It has become ubiquitous […]
Temporal and spatial aliasing in signal processing
The concept of aliasing is relevant to the oscilloscope user and unless it is confronted and steps taken to mitigate it, problems can arise in signal interpretation. Aliasing is almost always harmful unless clever ways can be devised to make use of it. When a signal is sampled, aliasing can appear in the end product, […]
