ORIGINAL MESSAGE:
On Wed, 14 Oct 2009 02:58:56 +0200, "DF3KV" <df3kv@t-online.de> wrote:
>The parallel resonant circuit will look like a very large resistor to the RF
>voltage.
>Circulating current is AC current times Q, but there is none or very little
>AC current.
REPLY:
AC current times Q is correct, but remember we are talking about a plate choke
which is virtually unloaded and has a very high internal Q. Don't confuse this
with the Q of the pi-network which is loaded by the antenna.
If you are looking at the LC combination from "outside" the pair, then yes,
they appear as a high impedance. Within the LC pair however, the circulating
current is very high at the frequency of resonance when it is unloaded or very
lightly loaded.
You can see this effect in your pi-net tank circuit if you disconnect the
antenna and drive it hard. The voltage across the tank builds up to spectacular
levels and the reason that happens is due to the very large currents within the
tank components, caused by the very high Q of the unloaded tank..
73, Bill W6WRT
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