[Amps] *** SPAM *** Re: Antenna traps

[Steve Thompson]

Ian White GM3SEK wrote:

> An L-network only has two variables, so the working Q is automatically 
> determined for you. With a resistive load, this is automatically the 
> lowest that can be achieved - so that is an advantage. The only case 
> where an L-network won't give the lowest possible Q is with certain 
> highly reactive loads... in which case, you need to switch to a totally 
> different configuration of L-network.
I disagree. I haven't time to try and remember how to do the maths, but 
looking at a Smith chart, I think a three element network can give a 
lower loaded Q if there is any reactance in either impedance. The 
difference might be minimal when the reactance is low, but I think it's 
there.

> 
> This last point is the major DISadvantage of L-networks: lack of 
> flexibility. There are a total of 8 different configurations, and they 
> all have a limited matching range. Between them, they can match any 
> impedance (except a 1:1 match requires theoretically zero or infinite 
> component values) but it's a matter of finding which one out of the 8, 
> and most practical L-network tuners can switch between a maximum of 2 
> configurations.  However, I'd conjecture that for any pair of 
> impedances, there will always exist at least one L-network configuration 
> that can match them at the lowest possible working Q.

I think not, except for the particular comparison of L against three 
element matching between two pure resistances.

Steve

> 
> 
>