On Dec 7, 3:05 pm, Keith Dysart wrote:
On Dec 7, 1:00 pm, Cecil Moore wrote:





Keith Dysart wrote:
If the 100 ohm line was only 5 degrees long, how
long would the 600 ohm line have to be to obtain
0 ohms at the input?

-jcot(5) = -j11.43 normalized to Z0=100 ohms

-j100(11.43) = -j1143 ohms at the junction

-j1143/600 = -j1.905 normalized to Z0=600 ohms

arctan(1.905) = 62.3 degrees of Z0=600 ohm line

Would the phase shift at the junction still be
36.6 degrees?

The new phase shift would be 90-5-62.3 = 22.7 deg.

62.3 + 5 + 22.7 = 90 degrees

So sometimes a 600 to 100 ohm discontinuity
produces a 36.6 degree phase shift and sometimes
it produces a 22.7 degree phase shift (and probably
any value in between).

That's right, depending on the electrical (and physical) length of the
100 ohm line, it will have different values of reactance as seen by
the 600 ohm line, therefore different phase shifts, all the way to
zero when the length of the 100 ohm line is 0 degrees and the
reactance is infinite (the 600 ohm line sees an open circuit). Say at
0+ degrees, -jX(C) = 1000000000; this is where you see it headed when
you look at the smith chart.

At zero degrees of 100 ohm line, you have 90-0-90 = 0 degrees at the
discontinuity.

AI4QJ