James M. Potter wrote:
There are two things to keep in mind when you put a coil in a can.

1. The inductance will decrease due to the reduced voulme for the
magnetic energy. This is the same effect as using a brass slug to
change teh inductance of a coil for VHF applications.
2. The losses will increase due to the induced currents in the walls
of the container.

What happens is that the metal acts as a shorted turn which absorbs some
of the current flowing in the inductor. A brass slug core inside the
coil takes advantage of this, the closer to the center of the coil the
greater the effect. The result is both a lowering of the inductance and
probably the Q. An effective way to tune vhf-uhf circuits, but a
shorted rotary turn was also used on the hf bands in "olden" days.
In the case of small tightly wound inductors with iron core slugs
the coupling from the shield can to the coil is rather small (ratio of
the turns and inductance) so the effect is small.

The further away the walls are the lower the effect. The various rules
of thumb you hear are just the result of someone determining what is
acceptable.

73 de K9GXC, Jim

On Fri, 02 Feb 2007 13:45:47 GMT, "Ceriel Nosforit"
wrote:

Quick, simple question:

Would a normal aluminum can be any good for RF shielding of a balun, or
would it for some reason not work? Should I connect it to ground?

And;
What does a transmatch do for me that a normal balun/transformer won't do
for me?

Thank you for your time.
Sincerecly,