impedance vs characterstic impedance

[myatham]

Hi,
Is there any difference between impedance and charasteric impedance? As per my understaning, impedance depends on frequency, but charasteric impedance is independent of frequency. So, i am assuming that both are not same. Please comment on this.

 

[Ow@i$]

U are right when u say it is independent of frequency but how actually is that !!!
It is because characteristic impedance is not reactive its resistive always so its independent of Frequency as well as length of the line...
whereas Impedance can be reactive thus frequency dependent.
They are also different as Characteristic impedance is impedance without reflection back (Which would eventually effect the source signal, changing the V & I ratio and thus Impedance)!!

 

[jiripolivka]

Oh, my! The "impedance" is a property of any component, antenna, simply anything. A typical impedance has the real and imaginary components, measured in Ohms.

The "characteristic impedance" is a feature of a transmission line. The "characteristic" means that it is defined by line cross-section shape and dimensions. Typical transmission lines have only the real component. For the purpose of connecting RF power and signal sources and tested components (with any impedance), lines have standardized characteristic impedance of e.,g. 50 Ohms, but for certain designs, 60 and 75 Ohms are preferred. Waveguides have other characteristic impedances that vary with frequency but remain real.