數碼同軸線問題

數碼同軸線個插頭係咪用rca頭,有冇分75歐姆頭

rca頭一樣是75ohm

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http://www.canare.com/ProductItemDisplay.aspx?productItemID=40
我剩係識呢隻,唔知幫唔幫到你

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Radio Frequencies: When an RF voltage and current are transmitted along a wire, the impedance of the cable itself becomes significant, and for any distance that is "significant" - which is to say any distance greater than about 0.1 of the signal's wavelength - matching is necessary. The wavelength is calculated from the speed of light (3 x 10 ^ 8 m/s, or 300,000km/s) multiplied by the "velocity factor" of the cable. This varies from about 0.7 up to 0.9 depending on the dielectric constant of the inner insulator and cable construction, meaning that a signal travels more slowly in a cable than in free air or space.

Wavelength = C / f         (where C = velocity and f = frequency)
A 1Mhz signal travelling in a typical coaxial cable (velocity factor of 0.8) will have a wavelength of ...

Wavelength = ( ( 3 x 10E8) x 0.8 ) / 1 x 10E6 = 240m
Based on this, any attempt to transport a 1MHz signal further than about 24m will start to cause problems unless the send and receive impedances are properly matched - not only to each other, but to the cable as well.

In the hi-fi audio world, this is not an issue, since this is 50 times the highest frequency we can hear, and few instruments create appreciable harmonics above 20kHz anyway. In theory, we could send an audio signal 12km without having to worry about impedance matching, although at extreme line lengths matching can reduce high frequency signal losses. To understand the reasons is beyond this article, as it involves transmission line theory - not one of the easiest concepts to grasp.

From: http://sound.westhost.com/impedanc.htm#rf

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在家做實驗,用條非75ohm的gotham線加普通頭和錫焊,但聲音尖了很多。之後用條幾蚊尺的Belden 75ohm線,用免焊的普通RCA頭,聲音又好接近家裡的同軸廠線。很有趣。

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回復 6 #wongck5

師兄, 請介紹免焊的普通RCA頭

via HKEPC Reader for Android

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回覆 7# iambbboy

其實都是鴨記普通幾十元一對的RCA頭,師兄最好抱住實驗心態,不過衰咗都冇乜損失。個個人要求不同

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回覆 6# wongck5

我反而有興趣想知 Coaxial cable 例如 色差線, Video cable 用於 Audio 適唔適合.  

唔想浪費當時千古 & 千辛萬苦買落畀 LD, DVD 的剩餘物資.  廿年前一千幾百嘅質素., 今天要畀多好多好多先可以買到

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用耳收貨。一樣有好多coaxial設計的音頻線,古董wbt2016就是。

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