This question is about high speed digital transmission on a transmission line, I need to know about how does the
(1) impedance of the transmission line and the (2) source impedance and (3) termination impedance,
effect the (1) cable length when we want to transmit a fixed high data rate, and also (2) effect data rate for a fixed length cable.
I understand you asking these sort of questions and I've tried to answer in the format that you presented the questions. Please forgive if I have misconstrued something.
Q1 - cable length when transmitting high data rate: -
(1) Impedance of the transmission line is independent of cable length
(2) Source impedance is independent of cable length
(3) Termination impedance is independent of cable length
Q2 - data rate for a fixed length cable: -
(1) Impedance of the transmission line is generally higher for better data success
(2) Source impedance can be zero for improved results providing the receiver has good terminator
(3) Termination impedance needs to be the correct value for the cable to minimize reflections corrupting the data
Q3: Termination is needed at the far end to stop reflections, especially for high data rates and long cables. The termination should be from the receiving end to ground.
The important thing for high speed communications is that the impedance of the endpoints closely matches the characteristic impedance of the cable. This minimises reflections.
The actual impedance of the line is mostly set by cable design constraints. The best balance of different types of signal loss is achived at impedances of the order of 50-100 ohms.
