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在短波电报通信用的接收机中,为了要增加中频放大器的选择性,通常采用高品质因数的晶体(石英谐振体)作为耦合元件,利用晶体的串联谐振回路的特性,可以得到很好的选择性.但是它们的分析和制造,通常利用四端网络的方法,即按所需的频率衰减特性计算出电参数,然后根据电参数来确定晶体的尺寸,这样一定会涉及频率系数和电感系数,尤其是电感系数,当在高频时很难确定,导致设计上的困难.
In receivers for shortwave telegraphy, high-quality-factor crystals (quartz resonators) are often used as the coupling elements in order to increase the selectivity of the intermediate-frequency amplifier. By using the characteristics of the series resonant circuit of the crystal, a good choice can be obtained However, in their analysis and fabrication, the four-terminal network method is usually used to calculate the electrical parameters according to the required frequency attenuation characteristics and then determine the crystal size based on the electrical parameters, so that the frequency coefficient and the inductance coefficient must be involved. The inductance, in particular, is difficult to determine when at high frequencies, resulting in design difficulties.