[Antennas] Q loaded versus unloaded

2003年10月01日 09:37:17 -0700

Dear Robert.
Many thanks for your kind answer and clear explanation, I did not realize=20
that it was so easy ... yes, unloaded=3Dalone, loaded=3D inserted into a=20
circuit .... great ...
I'm discovering a real wonderful world: antennas design and theory (always=
=20
since a long time ago I was surprise how the people could design an antenna=
=20
from the scratch, I have been so far just a builder of other's designs).
Now I'm reading W2DU "Reflections" and discovering misunderstandings that I=
=20
had in relation to the SWR and how to balance effort to reduce the SWR=20
versus real power gained.
Thanks a lot
Juan
At 30/09/2003, Robert Lay \(W9DMK\) wrote:
>Dear Juan,
><------------------------------------------------------------------------
>I'm in the process to understand in detail the basics of antenna theory and
>matching lines (transmission lines) and I have arrived to a point where I
>am a little bit confused:
>>Where could I find the difference between Q unloaded and loaded and their
>effects in the antenna design?
>------------------------------------------------------------------------>
>For an inductor (coil), in a theoretical analysis, the Q of the coil itself
>should be high, of course, in order to minimize loss. Any loss in the coil
>itself results in lower unloaded Q.
>>Once the inductor is "loaded" (a lossy element is placed in the same=
 circuit
>with the inductor), and a new Q is calculated based on that additional=
 loss,
>then the new value of Q is a function of the inductor's own losses and the
>additional losses of the rest of the circuit. However, we now are talking
>about the Q of the "circuit" - not just the Q of the inductor itself.
>><---------------------------------------------------------------------
>According to what I understood if the Q of a coil in the antenna is very
>high, the bandwidth decreases and losses too.
>-------------------------------------------------------------------->
>That is reasonable and true.
>> >--------------------------------------------------------------
>However in some articles
>related to tuners I found that coils with low Q reduces losses and it's
>better to use them ... is the "unloaded" versus "Loaded" present here?
>Anyone could be so kind to clarify me this point.
>---------------------------------------------------------------->
>>That makes no sense and I would appreciate a reference in order to
>understand the context.
>I believe there is a misunderstanding there.
>>Bob Lay (W9DMK) in Dahlgren, VA
>http://www.qsl.net/w9dmk

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