Impedance matching is necessary for regular transfer without reflected waves in HF range (c. up 10 MHz). On the other hand it brings decrease of tranfer -6 dB. Therefore it is betr to use Rin>>Rour for low frequenci range.

Dear Simeon,

This is a basic question concerning the source impedance.In general, any electrical source is characterized by an electromotive force which is the open circuit voltage of the source in addition to a source resistance. There is no standard specific values for the source resistance except for few communication systems.

An ideal voltage source has zero source impedance.The AC mains electricity supply can be considered nearly ideal voltage source with a very small source impedance.

Signal sources normally has a remarkable impedance. By signal sources, it is meant audio signal sources, video signal sources, data signal sources , radio frequency and microwave signal sources.

In communication, one uses transmission lines to covey the information signal from a n information source to an information destination. The transmission lines themselves are characterized by a characteristic wave impedance termed Zo. Two transmission lines were standardized as a transmission medium for the information signal. The coaxial cable with a characteristic impedance of 50 Ohms to convey high frequency signals.and a twisted wire pair with Zo= 600 Ohm to covey an audio signal,. These impedance values resulted from an optimum operation of the two media to transmit the signals.There may exist some other standardized Zo for new cables for new applications such as the local area network.

Whenever we apply a signal source on a transmission line, we have to connect them to satisfy the maximum power transfer condition from the source to the transmission line. This can be achieved by either making the source impedance Zs=Zo congugate the characteristic impedance of the transmission line. IF they are real they well be equal, or IF they are different one has to use a matching circuit between the transmission line and the signal sources. For more details on the matching circuits consult for example book Electronic communication techniques by Young.

The far end of the transmission line must be matched with the load to avoid reflections and transfer the maximum power to the load.

Also any circuit building blocks like filters, amplifiers, mixers and equalizers connected to a transmission line must be also matched to it to prevent reflections and transfer the maximum power.

I hope that i introduced here may be useful to you.

best regards

It is typical to use 75 ohm for radioelectronic because the tunned unipole antenna has this impedance.

Mr. AlDmour the frequency and impedance ((power capability + attenuation)/2) are different, just i want to know the what will be the impedance in power generation station and receiving at substation what will be the matching impedance.

i got some other information from tweet thank u for that