输出,输入阻抗设计

Shirley Post at 2006/3/14 16:31:00

根据传输线原理(transmission line), 输出阻抗=传输线阻抗=负载阻抗时, 信号就不会从负载反射回信号源(reflection).

1) 传输线的阻抗如何计算?

2) 为什么用75 ohm, 而不用50 ohm或其它值?

A: 1) http://fermi.la.asu.edu/w9cf/tran/

A Transmission line calculator, Version 0.3, Kevin Schmidt, W9CF

This is a little transmission line calculator applet. A number of the ideas were borrowed from TL.EXE by Dean Straw N6BV. The values of the built in cable attenuations were taken from that program.

To use this applet, change the values in the input fields, and click calculate. Most of the fields should be self explanatory but I'll elaborate a little more below.

1)视频:

   因为规定输出阻抗75欧姆, 无负载时标准输出幅度是2V(100% white),有负载时是1V, 所以输入端用75欧接地.

2)音频:

    规定输出阻抗是300 ohm~1k ohm, 输入阻抗>=10K ohm. 不一定要用47K接地, 只要大于10K就可以. 所以我们在测量音频时用最小值10K作为负载.
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