[Antennas] 468/Freq in Mhz

[Andy]

492/F is the half wavelength in free space, and an infinitesimally thin bare
wire would resonate at that length.

468/F is an empirical formula that works pretty well for most common wire
diameters and no (or very thin?) insulation.  If the non-zero wire diameter
is mostly what is responsible for the reduction from 492 to 468, then there
probably is a difference between thin wire and tubing.

But 468/F is just a starting point, and should never be taken as exact!

I do not know the precise mechanism that causes the difference.  I don't
think I have seen a formula that starts with 492/F and then adds terms that
depend on wire size (and other factors), to get from there to ~468/F.
Antenna length also depends on things like proximity to the surroundings.
Each of the sections of an antenna have capacitance to the rest of the
antenna and to remote objects, and inductance along the length of the
antenna wire, and these things all add up to make the thing resonant at some
frequency.

Andy