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

 To: amps@contesting.com Re: [Amps] *** SPAM *** Re: Antenna traps Ian White GM3SEK Ian White GM3SEK Fri, 16 Dec 2005 09:31:29 +0000
 ```Peter Chadwick wrote: >Rich said: >>** An L-network always has the lowest Q possible. Is mo' Q mo' betta?< >Rubbish. Do the math. The Q is the sq.rt of the impedance ratio -1. >So the bigger the impedance transformation, the higher the working Q. >In any two variable system, Qw is an uncontrolled variable. A 3 >variable network allows Q to be defined. That's the advantage of the T >or pi (which is the dual of the T). I think Rich is more right than Peter on this one. We all agree that the network should have the lowest possible working Q, in order to achieve the lowest possible internal losses and the highest possible power handling capability. When transforming between resistive impedances, the lowest possible working Q is: > the sq.rt of the impedance ratio -1 Any lower value of Q will not achieve a match. Any network with three variables (eg a T) can also achieve a match, but always with higher than the minimum possible values of working Q and internal losses. 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. 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. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps ```
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