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Here you should gain a full understanding of the selection and design basics for lc filters. These lc filters topics cover everything necessary for your continued understanding of radio design and transmitter design.
It is absolutely imperative you fully understand the basic terms capacitance, chokes, impedance, inductance, "Q", reactance, resonance and toroids to complete these very comprehensive tutorials.
We will start with low pass filters (LPF) because they are the basis of other filter designs. High pass or band pass filters are often simply transformations from low pass filter designs. It is simply two L networks added together.
With the addition of one small component, a capacitor, we can transform a low pass filter into a filter with near infinite attenuation at a designed trap frequency. I call this an "harmonic trap filter".
LC Band pass filters are usually LC filters containing resonator combinations of inductance and capacitance which are designed mathematically to respond to design frequencies while rejecting all other out of band frequencies. Because LC bandpass filters have inherent limitations these statements should not be taken too literally.
This LC and crystal filter software was written by Neil Heckt of Almost All Digital Electronics as an aid for filter designers to simply plug in various filter parameters and hey presto! there is your finished design. I will present you with the design example of a crystal filter of the crystal ladder filters variety as designed on my evaluation copy of the downloaded software.
Assuming you have mastered the design of low pass LC filters we will now proceed to the design of a high pass filters. A high pass filter is simply the transformation of a low pass filter. Just as one high pass filter design example, we will say we need a five pole butterworth filter with a cut off frequency Fc at 2000 Khz. That is we want to pass all frequencies above 2000 Khz but attenuate those below 2000 Khz, that is the function of a high pass filter.
IF amplifier filters are LC resonator stages separated by individual stages of amplification. The principle is called synchronously tuned filters stages. In IF amplifier filters there can be any number of resonators per individual stage.
Active bandpass filters are simply filters constructed by using operational amplifiers as active devices configured to simulate inductors or what are known as "gyrators". Active bandpass filters are used largely at audio frequencies where otherwise the size of the inductor would become prohibitive. The are many different types of active filters including high pass, low pass, band reject and there are numerous responses including multiple feedback bandpass (MFBP), dual-amplifier bandpass (DABP) and, state variable bi-quad all pole circuits. Interestingly all known filter responses such as Butterworth and Chebyshev may be synthesised.
Narrow band filters are filters where the fractional bandwidth is extremely small in a relative sense. My personal definition of a narrow band filter is where the narrow band filter has a fractional bandwidth NOT exceeding 1%. A filter with a bandwidth of 200 Khz ( ± 100 Khz ) centred around 7100 Khz would represent a bandwidth of about 2.86% Here I present a very detailed design of a Butterworth narrow band filter.
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