AI4QJ wrote:
The close spacing of the coils reduces the time delays because the current
is "pushed along" faster.

This is true to a certain extent but not to the extent
that coil#1 couples heavily to coil#100 which is ten
inches away in W8JI's configuration. The 3 nS "measured"
delay at 4 MHz is off by approximately a magnitude. It
is much closer to 30 nS than it is to 3 nS.

I measured a ~25 nS delay in a 75m bugcatcher coil.
--
73, Cecil http://www.w5dxp.com