[600MRG] Noise Issues.

[Claude Baker]

Ken,
 Responding to your final question, 

"Does anyone here know if an inductively coupled dual-loop was ever used, 
and what might have been its purpose?"

Many moons ago I worked on a military VLF receiver system that used a pair 
of shielded crossed loops along with a whip for sense. The loops were 
each each 7 turns with an additional single turn loop included inside 
the shield. The single turn and 7 turn were not electrically connected 
but were of course inductively coupled.  The single turn loops were used for injecting calibration signals check the DF circuitry function. 


The calibration signal was a sub-microseond pulse which made the tuned 7 
turn loop ring; they were tuned to 10KHz, Q of 3.3. With a single, in 
circuit pulse generator, a transformer and a set of relays, we rotated 
an 8 position switch to check the 45 degree spaced cardinal points on 
the compass.

During a physical calibration, we applied a signal to the N-S loop and tweaked (rotated) the E-W loop to get a minimal signal. Ideally, the E-W loop 
would see no signal when the N-S/E-W loops were perpendicular.

The calibration described has absolutely no bearing on correct "aiming" of the system

 Claude Baker, AC0ZL