Jim wrote...
My purpose is for impediance matching, from 50 ohm cable
to a 0.5 ohm load.
You could simply put a 50-ohm resistor in series with your
o.5-ohm load, to prevent reflections and insure a fixed
known current at all operating frequencies.
As far as wideband transformers are concerned, the common
4:1 transmission-line transformers (get Sevick's books) can
be made for 50 to 12.5 ohms and then 12.5 to 3.25 ohms. The
transmission line in each stage must have an impedance that's
the geometric mean between Zin and Zout, i.e. 25 ohms and
6.5 ohms. You'll have to make the transmission line yourself.
I handmade a 16:1 wideband transformer this way, and it was
a tricky task, taking several days. But it worked well.
In theory you can do the next step from 3.25 to 0.81 ohms,
but it's nearly impossible to make 1.6-ohm transmission line.
Perhaps the spot for a resistive match is here, at the 3.25
to 0.5-ohm level. At least you will have quadrupled the
delivered current into 0.5 ohms with your 16:1 transformer.
If you want to play a narrow-band matching game, no problem,
have at it.
