Electrical Wave Filters Employing Quartz Crystals as Elements

Abstract

This paper discusses the use of piezoelectric crystals as elements in wave filters and shows that very sharp selectivities can be obtained by employing such elements. It is shown that by employing crystals and condensers only, very narrow band filters result. By using coils and transformers in conjuction with crystals and condensers, wide-band-pass and high and low-pass filters can be constructed having very sharp selectivities. The circuit configurations employed are such that the coil dissipation has only the effect of adding a constant loss to the filter characteristic, this loss being independent of the frequency. Experimental curves are given showing the degree of selection possible.