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电视机的有限噪声灵敏度是电视机最重要的性能规格之一,其定义及测量方法,各国都大同小异。一般采用三阶梯波或正弦波作为调制内容,但调制度和信噪比的读取方法等各国标准略有不同。我国四机部部标 SJ-949-75(黑白电视广播接收机的测量方法)中对这一性能规格的定义及测量方法也作了清楚的规定,即这项性能的两种方法同等有效。实际上两种波形调制后的射频波形并不一致,因此在测量时电视机的工作状态并不完全相同,测量结果必然会有偏差,其偏差与电视机 AGC特性有关。我国各工厂过去普遍采用三阶梯波形法,但随着 UHF 频段的应用和在国际交往中将逐渐采用正弦波形法,所以有必要作一番探讨。本文还对电视机有限噪声灵敏度的计算公式进行了推导,并与一般的接收机灵敏度公式进行了对比,发现公式的形式是一致的,但参数的含义有所不同。
The limited noise sensitivity of televisions is one of the most important performance specifications of televisions. The definition and measurement methods are the same in all countries. The general use of three ladder wave or sine wave as the modulation content, but the degree of modulation and signal to noise ratio read the national standards and other slightly different. The definitions and measurement methods of this performance specification are also clearly defined in the standard of SJ-949-75 (Measurement Method of Black-and-white Television Broadcasting Receivers) in the four-machine department of our country. The two methods of this performance are equally valid. In fact, the waveform of the two waveforms is not consistent after the RF modulation. Therefore, the working status of the television set is not exactly the same when the measurement is performed, and the measurement result is bound to be biased. The deviation is related to the AGC characteristics of the television set. However, with the application of UHF band and the gradual adoption of sine wave method in international exchanges, it is necessary to make some discussions. This paper also deduces the formula of the limited noise sensitivity of the TV and compares it with the general receiver sensitivity formula. The formula of the formula is consistent, but the meaning of the parameters is different.