Why do we take characteristic impedance to be 50 ohm ?

[myem]

characteristic impedance

why do we take characteristic impedance to be 50 ohm ?
where could I get relative reference ?

THX

 

[chaiyuliang]

characteristic impedance

It is based on the common circuit design experience

 

[adrastos]

Re: characteristic impedance

Hope this help !!

**broken link removed**

 

[myem]

Re: characteristic impedance

thanks for your reply
this article is just explained by words.
is there any related article about math ?

Added after 31 seconds:

thanks for your reply
this article is just explained by words.
is there any related article about math ?

 

[pimr]

Re: characteristic impedance

hi,
50ohm is not necessary,75 ohm is also standard in lot of cases.
neways the principle behind it is maximum power transmission theorem which states that maximum power is delivered to load when its impedance is equal to the impedance of system.
Since co-ax cables are made of material such that their charecteristic impedance which is also calulated from a formula(u can get it in any book on electromagnetics) is 50ohm and in order to deliver maximum power it should be matched with a load of 50ohm.
If u use some other cable having different characteristic impedance u have to change the load accordingly.In industry generally 50ohm and 75ohm are standard.hope this helps.
regards
pimr

 

[yesman]

characteristic impedance

Agree with Pimr. 20-50 ohm characteristic impedance are still used in some radar system. Because it can get the best performance and easy to connect.

Added after 5 minutes:

In practical engineering, co-ax cables are not equal 50 ohm usually. They are more or less than 50 ohm.

 

[j2005]

Re: characteristic impedance

It all boils down to basic transmission line theory. The idea is to match the impedances so that you minimize losses and relections. Excessive reflections can mess up your original signal. Think of these signals like an echo. Once your voice signals hits another medium of different impedance, e.g. a wall, it bounces back and your original message gets garbled up. So if you can keep the impedance the same, you'll allow the signal to propagate properly.

Do a search for transmission line theory to get the maths. It's a whole lot of Zs and trigonometry for you to digest. Or get hold of a book. Good luck!

Please click "helped me" if you think this is of any help.

 

[adrastos]

Re: characteristic impedance

Hi, I guess I misunderstand your question. I thought you mean why 50ohm is the standard impedance. From what I know, it is a trade off between high power handling capability (35ohm transmission lines) and optimal matching (75 Ohm to dipole).

To answer the question better (mathematically), you can solve a circuit with an ideal voltage source having a source impedance Zs connecting to a load impedance ZL. You will find that for maximum power transfer to the load, it is required to have Zs = ZL*. It is often refer to as conjugate matching. You should be able to find this from most microwave engineering books.

 

[bhgaurav]

characteristic impedance

it depends on your design and components. well most designs in real world are done with characteristic impedance 50 ohm

 

[mreza1355]

Re: characteristic impedance

This is the real answer of your question