I respectfully submit that none of that makes any sense in the context
of a dummy load.
A dummy load isn't resonant, it's resistive. It's a big ol' resistor
mounted in some sort of heat-dispersing set up. When the other poster
said he read 55 + j0 he wasn't kidding: The zero part of that means
that it's a resistive measurement. A negative j (or i, if you're a
math major) means the system is more capacitive, a plus j is more
inductive. A zero means it's neither from a practical point of view.
Or so they told us in college.
Jeff/KD4RBG
---- Original message ----
>Date: Fri, 7 Aug 2009 14:17:47 -0500
>From: "Perry - K4PWO" <k4pwo@comcast.net>
>Subject: Re: [TowerTalk] Resonance is over rated
>To: "Scott McClements" <kc2pih@gmail.com>,<towertalk@contesting.com>
>
>Resonance, in the normal sense has nothing to do with the value of impedance
>only in a minimum (for a series tuned configuration) or maximum (parallel
>tuned). While its possible to make the argument that a dummy load is a
>resonant "antenna" with a Q of 1 (Q=Fr/BW or infinity/infinity) the concept
>of a "resonant frequency" of infinity is counter intuitive. Since "dummy
>loads" are made with real world components, we know that the "resonant
>frequency" can not be infinity. So in that sense, the "dummy load" is a
>very low, non unity Q "resonant circuit" but it fails in fitting a second
>order differential equation for circuit analysis. If the shoe doesn't
>fit...
>That still doesn't negate the fact that radiation efficiency is the key to
>propagating a signal.
>BTW, I operate a fairly effective "dummy load" on HF... a B&W BWD-180
>terminated folded dipole. It's pretty flat from 1.8 to 30 MHz. but its
>efficiency is all over the place in that range.
>It works but...
>
>73 de Perry - K4PWO
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|