On 28 Apr 2007 21:32:18 -0700, Bill Bowden
wrote:

Does anyone know why the distributed winding capacitance of a loop
antenna, or any inductor, degrades the efficiency?

Hi Bill,

For the usual reasons: Resistance (not capacitance).

It would seem that a loop antenna with 100pF of winding capacitance in
parallel with a external capacitor of 200pF would resonate at the
same frequency as a antenna with no winding capacitance and a external
capacitor of 300pF,but apparently that's not the case.

It could be the case, your mileage may vary.

The best explanation I got was that winding capacitance represents
'low Q' and a external tuning capacitor represents ' High Q'

You got bum explanations then.

What is the difference between high and low Q, and why should a loop
antenna with no winding capacitance perform any better than one with
50% of the total capacitance in the windings? Where is the energy
loss?

It seems you may be, instead, writing about Unloaded and Loaded Q.
Loaded Q would be that found in service (in the actual application,
whatever that might be). Unloaded Q would be that found at the bench
with no other attachments. The Loaded Q's lower value is due to the R
of the "load" ...as it stands to reason. That load will be an
antenna's radiation resistance (and any Ohmic loss of the structure).

The energy loss is called radiation - if you do it right.

73's
Richard Clark, KB7QHC