On Wed, 15 Feb 2006 22:44:00 GMT, Cecil Moore wrote:


It might be interesting to some to explain how/why this works.
....

Some thoughts on why it might not work to plan, though it should be
close to plan and capable of fine adjustment if needed.

Worth noting that the characteristic impedance of some lines is quite
different to their market labelling, especially 300 ohm and 450 ohm
lines.

In this part of the world, nominal 300 ohm TV ribbon is more like 360.
Wes measured a range of nominal 450 ohm lines to be from 360 to 400
ohms.

Although the calculated answer might be a shunt capacitor of 147pF, in
practice a close value would be used and both the dipole length and
feedline length could be juggled for better match if needed.
Alternatively, a shunt stub could be used and tuned along with the
series line length.

The feed point impedance of the dipole will depend on its environment
to some extent, and may be reactive if formulas are used to cut it to
length.

Of course, it is a one-band matching arrangment.

Owen
--