[TenTec] OT Antenna Tuners

[Dr. Gerald N. Johnson]

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