Jerry Martes wrote:
Is it posible that the length of the "stubs" change? I'd have thought the
length of the stub is always the same. 45 degrees should always be 45
degrees, shouldnt it?? An open circuit, 45 degrees back along a 50 ohm line
looks like 50 ohms capacitive. That 50 ohms looks like something like 500
ohms inductive as viewed 45 degrees back along a 600 ohm line.
I'd guess your point is that 500 ohms of pure inductive reactance is never
seen 90 degrees back from an open, no matter what the Zo of the line

The point I'm eventually going to make is about loading coils
in mobile antennas but let's stick with the above stub example.

| 45 deg | 45 deg |
Source====Z01=========Z02====open

Z01 = 600 ohms, Z02 = 50 ohms

If the Z0 were constant and the stub was 90 degrees long,
the source would see zero ohms. Yet in our above example
the stub is physically 90 degrees long and the source sees
+j500 ohms. The above stub is electrically 130 degrees long.
There is a 45 degree delay through the Z01 section of stub.
There is a 45 degree delay through the Z02 section of stub.
There is a 40 degree phase shift at the Z01 to Z02 junction.

If we want to turn the above stub into a functional 1/4WL
open stub such that the source sees zero ohms, we can
remove 40 degrees from the Z02 section. If we make the
Z02 section 5 degrees long, the entire stub will be
electrically 90 degrees long, and 1/4WL resonant.
There will be a 45 degree delay through the Z01 section
There will be a 5 degree delay through the Z02 section
There will be a 40 degree phase shift at the Z01 to Z02
junction.
--
73, Cecil http://www.qsl.net/w5dxp