![]() ![]() Several types of responses are shown in Figure 2. (The phase response is also important in many applications.) This is the filter’s frequency response and because it describes signal amplitude, it is a magnitude response. Nearly all electrical filters (assume we are talking about electrical filters from this point on) are described and specified by their effect on the amplitude or magnitude of signals having different frequencies. This article will stick with the traditional analog circuits, but the general definitions and specifications for how the filter behaves apply to all filters. Processing and converter electronics are now inexpensive enough to implement that digital filters (and many other signal-processing functions) are taking over from analog in ham radio. If the result is to be viewed or listened to by a human, the digital data is converted back to an analog signal. Once digitized, any mathematical operation can be performed on the data. Filter B (bottom) is an active low-pass op-amp filter typically used for audio signals.Ī digital filter requires analog signals to be digitized, creating a stream of digital data representing the original signal. Filter A (top) is a passive high-pass LC filter used for rejecting AM broadcast band signals. Figure 1 shows an example of each type of filter circuit.įIGURE 1. Most active filters use op-amps in a variety of feedback circuits. If some kind of amplifier is used, the circuit becomes an active filter. The common passive (unpowered) analog filter consists of familiar inductor-capacitor (LC) or resistor-capacitor (RC) circuits. Analog and Digital FiltersĪs with just about everything else in ham radio, filters can be analog or digital. All three of those characteristics are basically the same thing: a regular variation in time. With respect to electrical signals, a filter is a circuit or function with an effect that varies with the input signal’s frequency, wavelength, or phase. The general idea, though, is to operate on an input signal (or data) so that the output is modified based on some pre-defined quality of the input signal. Looking up “filter” generates a lot of entries! Along with the electrical definitions, there are adaptive filters and image filters and so forth, as well. This is true at the system level, just as it is at the circuit level - and many circuits behave in a filter-like way, whether intended to be a filter or not! That makes understanding filter basics important for wireless success. A casual observer might think that wireless systems consist primarily of filters connected by the occasional bit of circuit! Block diagrams of transceivers often include as many filters as any other function.
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