Tom Donaly wrote:
O.K., Cecil, I finally figured out what you want to do. You want
a zero ohm input impedance, just like a 1/4 wave open stub. In that
case, you're absolutely right, the 600 ohm line should be 43.387
degrees long. If you call the 100 ohm line, line 1, and the 600
ohm line, line 2, then the criterion for what you want is:
tan(Bl1)*tan(Bl2)= Z01/Z02. This behaves sort of like a backwards,
transmission-line, Helmholtz resonator. I still don't know where you
come up with the 90 degree stuff.

For an open stub to exhibit a zero ohm input impedance,
it must be electrically 90 degrees long (or 270 ...).
That's where the 90 degrees comes from. The example
stub is electrically 90 degrees long while being 53
degrees long physically.

Good for you, Tom, now you have it - "just like a 1/4WL
open stub" from 53 degrees of transmission line. Here's
another tidbit for you.

Using 600 ohm line and 100 ohms line, if you make the two
sections equal length, the dual-Z0 stub will be very close
to 1/2 the physical length of a single-Z0 stub, i.e. physically
45 degrees long for an electrical 1/4WL (90 deg) stub. On 75m,
that cuts the 1/4 stub physical length from ~66 feet to ~33
feet, a much more manageable length.

Here's a useful equation. For a 1/4WL stub with equal length
sections, the physical length in degrees of each section is:

ARCTAN[SQRT(Z0Low/Z0High)]
--
73, Cecil http://www.w5dxp.com