[600MRG] Loop ground planes ( on aeroplanes )

[Dave Riley]

Re: Loop ground plane...

In the early days of aircraft radio one would find a small manually 
steered loop overhead of the pilot. This was during the rag wing era 
with no noticeable ground plane.
Then the same loop was joined along with a 'sense' wire antenna so that 
one loop null could be filled while the other null was made deeper.
The 'sensed' version could home in well on a non directional 'NDB' 
station to very good advantage with little probability of flying in the 
wrong direction and even to manually set the loop null abeam the 
aircraft for a 'marker' when passing a station.
It is thought that the "Lady Be Good' was a victim of this kind of error.
https://en.wikipedia.org/wiki/Lady_Be_Good_(aircraft)
Along comes automation.
Around the 1940s automated loops ( automatic direction finders ) made 
their way in with the ARN-6 and 7 radios. These loops were encased in a 
graphite like aerodynamic teardrop enclosure, further the loop was wound 
in a small diameter <1' and motor driven on a split bobbin because 
electrostatic noise was a real buggar to get rid of.
Eventually loops were made flush with the fuselage and were wound 
internally with 3 phase fixed windings modulated by the ADF receiver 
which resolved the received direction very accurately.
If you get a chance to see or even procure one of these surplus aircraft 
loops and hook it up to your MF receiver, you will be amazed @ the lack 
of noise. They really worked well. The above were good from 180kc. ( 
consolan ) to the broadcast band, covering the 600m emergency direction
finder frequencies...
Just some background for thought... This TX loop essentially sees silica 
sand down to a good depth ( insulator )...

Tnx from DaveR /17