One of the beauties of the L network is that we have a choice of values for
the L and C depending on their location or position relative to each other.
This makes it possible to choose the lowest loss configuration from the mix.
If it is a Ten-Tec model 238 or 235, and probably also 229, there are
only two configurations available. Those two configurations both have
the L in series. The shunt C can be switched to either the source or the
load end of the L. (There is also a very small L in series on the
opposite side of the C, which makes it actually a T network. This L is
so small that it serves mostly to counteract stray or minimum
capacitance. This makes it so that there is not an unobtainable tuning
zone between the two configurations.) For either configuration there is
no more than one setting of the L and C that gives a match. In some
cases there may not be enough L or C to get a match in one of the
configurations, or perhaps not in either configuration. In any case,
when you do find match, it is never a really high Q match, and there
will not be really high circulating currents or high voltages. The two
configurations available may not alway be the lowest loss configurations
possible using only two elements in a L network, though they are usually
pretty darn good. It is simple and effective.
DE N6KB
|