I recently came up with a useful trick for dealing with a problem that has
troubled me and other homebrewers for years, so I though I would pass it on to
the universe.
While installing some wiring in a new amp project, I needed a source of 50
ohm coax that was small and flexible to facilitate routing it thru holes,
around
corners, etc. I ended up homebrewing some using standard components de junque
as follows. The method is fine for fabricating pieces up to 5 or 10 feet long.
First, take a piece of RG58 and strip away everything but the shield (it is
easiest to first strip off the outer jacket.) Then pull through the shield a
piece of #20TEW Teflon jacketed hookup wire, and pull the shield tight. This
happens to form a coaxial line of close to 50 ohms Z-sub-zero. I checked the
impedance from 5-100 MHZ with a meter and it runs about 52-53 ohms.
I also connected a short piece between an amp and a dummy load, and ran it
for a few minutes at 900+ W. There was only the slightest hint of heat, so
power handling capacity at 1KW looks fine.
This configuration is really a good solution for building Toroidal baluns,
since it can be easily wound on relatively small cores with little more effort
than hook up wire. For baluns, the outside has to be insulated, for which small
hollow tubing works well. I prefer the 1/8" Polyester mesh, which fits
nicely. Or, just wrap it with electrical tape.
73
Eric von Valtier K8LV
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