[Antennas] Re: From transmission lines to tuners;Simulator

2002年12月19日 09:03:23 -1000

Interesting discussion. Of some help, might be to experiment
a bit with a T network tuner simulator, one is available. Go to:
http://fermi.la.asu.edu/w9cf/tuner/tuner.html
You can adjust everything, including the Q of the components!
Brief instructions are given, you will learn some stuff, hi.
Interesting that the highest efficiency in the network almost
always will only occur when either the input or output series
C element is set to its' maximum value. And in some cases,
you will probably need more capacitance than a given tuner's
components might have available!
The Simulator Set Up button allows you to change the maximum 
values of the three components and their Q values. Initially the 
capacitors are 250 pF, Q=2000 and the coil is 30 microH, 
with Q=100. 
Wes has commented on this aspect in his post; see,in part:
> With decent components in the tuner (not all of them have 
> them) the inductor will generally be the biggest contributor to 
> insertion loss. This results from the fact that the unloaded Q 
> of most capacitors is much greater that that of the inductor. 
>> Absent voltage breakdown in the components, it is the increased 
> circulating current in the network that is the major contributor to 
> loss. With a give unloaded Q, the loss will increase when the 
> loaded Q increases. With a network comprised of three variable 
> elements there are in theory an infinite number of settings that 
> will effect a match between two impedances. Each of them will 
> have a different operating Q, so the object should be to adjust 
> the network for a match with the lowest network Q.

Experiment with Q values with the Simulator to see what happens
to the network efficiency.
73, Jim KH7M