On Sun, 2008-07-20 at 18:59 -1000, Ken Brown wrote:
> > 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.
That's not necessarily true. The loaded Q depends on the impedance
ratio. The higher the ratio, the higher the loaded Q. So for a large
impedance ratio, there has to be a high loaded Q and large circulating
currents. In the L they will always be smaller circulating currents than
a PI or T, but they won't necessarily be small.
> 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
73, Jerry, K0CQ
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