[Elecraft] OT: SGC Coupler / Small Wire Loops

[Tony Wells]

Ron wrote:

>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

Hi Ron,

Can you expand on that a bit - are we talking high voltage and high current
90% out of phase here?

Regards,

Tony

All mail in and out checked lovingly by hand, character by character.

----- Original Message -----
From: "Ron D'Eau Claire" <rondec@easystreet.com>
To: <elecraft@mailman.qth.net>
Sent: Thursday, March 27, 2003 11:59 PM
Subject: RE: [Elecraft] OT: SGC Coupler / Small Wire Loops


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...

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

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