RadioBanter - View Single Post - How to match 190 +j140 to a 50 ohm source?

Richard Clark · December 8th 07, 05:13 PM posted to rec.radio.amateur.antenna

On Sat, 8 Dec 2007 06:58:33 -0800 (PST), wrote:

that about sums it up.

stub matching looks attractive, but how do I actually build one of
these suckers?

Using two lengths of transmission line that you have to cut to length,
or build them so that they slide like a trombone.

Do I have to carve out a piece of coax and then fit
another one into it, if that makes sense? Won't that be nearly
impossible to solder?

The trombone line will probably more successful, although more
difficult to accomplish. You would build it out of brass, staged
tubing (4 diameters), with BNC connectors at each end. All quite
complex as I said, but it would suit a far wider range of matching
applications. You would also need a shorted BNC to terminate one of
the trombones so that you had that variation covered too. Use a T
connector set a the end of the drive line, one trombone line goes to
the load, and the other goes to the remaining T connection. You might
be able to get away with this last trombone section and just use the T
and a short run of standard coax to the load - emphasis on "might."
These two trombone lengths should have the capacity to vary over a
range at least slightly greater than half a wavelength. You will want
to build them longer for mechanical reasons. The sliding contacts
will not be very reliable (professional tuners have spring loaded
surfaces).

Welcome to the wonderful world of double stub tuning.

Gamma matching at the antenna would make this vastly easier.

73's
Richard Clark, KB7QHC