Locate a tuning fork. Mount it any way you please. Then check it from
time to time to see if it spontaneously begins a sustained ringing.

As a mechanical engineer, you're well acquainted with the differential
equations that describe the motion of a physical object that's been
struck, for example a tuning fork. And you'll recall that the form of
the solution is a decaying sinusoid. An antenna or other resonant
circuit obeys the same equations and behaves the same way. In electrical
parlance, this response to excitation is called "ringing", after the
obvious physical equivalent. While a tuning fork or an antenna will ring
if excited, an antenna won't spontaneously ring, or produce a sustained
oscillation without an external source of power -- for exactly the same
reasons a tuning fork won't.

Roy Lewallen, W7EL

Art Unwin KB9MZ wrote:

Richard,
If I have a loop circuit unconnected to a transmitter
could it not oscillate under ideal conditions?
If it can then would it not radiate at the frequency
that it is resonant at as well as reradiate at the
frequency of the energy input
Regards
Art