fair weather current

[Mike O'Dell]

i remember a construction article in a Popular Electronics
from my youth that measured sferic currents. i remember
it was a transistor differential amplifier driving a
small panel meter using two transistors (TO-5s) pushed 
into a small pill cap full of paper pulp mush so when it 
dried, they were insulated and temperature coupled. the "antenna" 
was a funnel-shaped fan of solid copper wires with
the ends sharpened, all tied together soldered
to the center conductor of coax. the othere side
was a driven earth ground, of course. 

the JHU-APL did work back in the 70s with an autopilot
demonstrated using R/C technology. there were "pickups"
on the wing tips and tail. the pickups had a little 
low-level radioactive source mounted on a mesh screen.
the three pickups fed MOSFET amplifiers and the differences
drove the aeleron and elevator servos. if the tips were
at the same height from ground, the difference would
be zero, so that levelled the wings. the difference
between the average of those two pickups and the
tail pickup drove the elevator servo, so that produced
level flight (some offset adjustments were necessary
to trim things out). they built a .60-class R/C plane
as a test platform with a *big* fuel tank. they broke
records for sustained time aloft and longest sustained
flight. and that was almost entirely with the "e-field
autopilot" doing the work of maintaining attitude.

it was written-up in a couple of magazines with lots
of technical details - enough so that reproducing it
was not all that hard. 

this was well before GPS

     -mo