Over the years Allen Avionics has
used its experience and knowledge to supply customers with a
comprehensive catalog that is easy to use and filled with valuable
information. By reading FILTER FACTS, you will gain a good general
understanding of LC Filters and some of their applications. This should
also help when you have a need for special or custom filter designs.
Allen Avionics Engineering and Sales Staff will be glad to answer any
questions that you may have regarding our filter products.
An LC Filter
may be defined as a passive device consisting of capacitors and
inductors in a particular array such that a group of specified
frequencies pass with very little attenuation while the undesired
frequencies are attenuated. The four most common types of LC Filters (Lowpass,
Highpass, Bandpass, Band Reject) are described on the following
illustrations. The ideal filter would be a device that exhibits no
attenuation in the passband and infinite attenuation to all other
frequencies. However, a filter with these characteristics cannot be
manufactured. Allen Avionics uses state-of-the-art computer aided design
and filter modeling to produce the highest quality LC Filters available.
The amplitude response of a filter from its passband to its reject band
is defined by its shape factor. In the catalog, the Lowpass and Highpass
Filters have their shape factors expressed as the ratio of the 20dB and
40dB frequencies to that of the 3dB frequency. For example: a Lowpass
filter with its cutoff at 1MHz and its 20dB point at 1.6MHz has a ratio
of 1.6 at 20dB. This can be found by dividing the 20dB frequency by the
3dB frequency i.e. (1.6MHz/1.0MHz) = 1.6 When a Highpass Filter is used,
the ratio is expressed as a number less than one. The cutoff ratios of
Lowpass and Highpass filters that Allen Avionics can manufacture are
listed in the tabulated listings for Lowpass and Highpass filters.