transmission lines

[audioguru2]

Hi Ante,
A short is zero ohms resistance to DC and is zero ohms impedance to AC.
If the impedance of a transmission line matches its source and termination resistances then its length doesn't affect the impedance.
A transmission line is many series inductors with many distributed bypass capacitors along its lenth, forming a lowpass filter that has a very high cutoff frequency. 

 

[ante1]

OK, and at which frequency does the 50 and the 75Ohm wire put up zero Ohms impedance?

 

[audioguru2]

OK, and at which frequency does the 50 and the 75Ohm wire put up zero Ohms impedance?

If the transmission line coax cable is 1/4 wavelemgth long then if its far end is open its close end will appear as a short.

 

[ante1]

That didn’t exactly answer my questions.  :-\

 

[AN920]

That you can calculate from the well known formula wl=speed of wave/frequency
wl = full wavelength in m
speed = 3 X 10 ^8 m/s
frequency of operation in Hz