[Elecraft] OT: SGC Coupler / Small Wire Loops

[Ron D'Eau Claire]

A high "Q" resonant circuit, which one had better hope a small "mag =
loop"
is, will have very high peak voltages followed by very high peak =
currents.
Remember, the circuit is oscillating! All the energy is stored up as a
charge in the capacitor, then it discharges through the coil producing =
...
.uh.... I believe the technical term is "HUMUNGOUS" currents flowing in =
the
wire which transfers the energy to a magnetic field around the antenna. =
As
the current drops because the capacitor is discharged, the magnetic =
field
collapses producing a reverse current in the wire that then recharges =
the
capacitor. And on it goes, like any "tank" or parallel-resonant circuit.
Some of the energy gets radiated and some gets lost in the resistance of =
the
wire and in any leakage across the dielectric of the capacitor. The less =
the
loss to the wire and dielectric, the more there is to make =
electromagnetic
waves with...=20

And since these are RF currents, they all crowd in the outer few atoms =
of
the wire, meaning that you get ... er... here's that word =
again...HUMUNGOUS
resistive losses unless you have a superconductor handy. Air is a darn =
good
dielectric - until it ionizes - so the bulk of the losses will be =
resistive.


The bigger the loop, the lower the Q and the lower the Q, the lower the =
peak
voltages AND currents. So the bigger the loop, the lower the resistive
losses.

Ron AC7AC
K2 # 1289



-----Original Message-----
...I have to ask  - Mag loop users will have noticed the phenomena of
extremely high voltages across the loop capacitor - hence the need for
high-voltage capacitors when high powers (greater than 20-50 W ) are =
poured
into the system. How do you reconcile that high-voltage with the
"conventional wisdom" of the need for low resistance to achieve high
current.

Regards,

Tony
M3CJF
G7IGG