Characteristic impedance

Thread Starter

bug13

Joined Feb 13, 2012
2,002
Hi guys

Today, my mind wonder away (as usual), I was thinking for a cable transmitting signal, is it better to use a high characteristic impedance one, or a lower one?

Just like we want as small resistance as (practically) possible in power cable.

Thanks guys!!
 

wmodavis

Joined Oct 23, 2010
739
Use whatever characteristic impedance cable which will effectively match to the impedance of the load with minimum reflected power. Also it is beneficial to use cable with the lowest loss at the frequency of interest. Very different issue than power loss due to current flow in low frequency power distribution systems.
 

crutschow

Joined Mar 14, 2008
34,280
A low impedance line doesn't necessarily result in lower losses for RF signals. The choice of impedance depends upon the application. Here's a discussion for coax cable.

Folded dipole antennas have an impedance of 300Ω and in the early days of television 300Ω twin-lead was often used in fringe are reception for minimum signal loss. Twin-lead is still used today in some RF applications for low loss.
 

alfacliff

Joined Dec 13, 2013
2,458
75 ohm coax has lower loss then 52 ohm because the capacitance per foot is lower. 300 ohm twinlead has much less loss than coax. check out the coax suppliers for more information.
 

crutschow

Joined Mar 14, 2008
34,280
So how about for audio? Is there a best characteristic impedance?
Not generally. Characteristic impedance is usually only of concern at high frequencies where it length of the line is a longer than a fraction of the electrical wavelength of the highest frequency signal which only occurs for very long lines at audio frequencies. The only audio impedance standard is 600Ω and that's not much used anymore. Here's a discussion on that.

For audio equipment there's no reason to match impedances in modern equipment. Power amps, for example, have an output impedance much lower than the speaker impedances to damp speaker resonances.
 
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