[Lowfer] WA tests

[Bill Ashlock]

Jay,

>Please let me know what you're going to use for sequencing.

I think I have come up with a solution for the loop/loop coupling problem 
but need some time to implement. We are getting lots of wet snow today and 
this makes it hard to run the outdoor tests needed to be sure it's working. 
The snow should end later today.

I set up a simulation of the problem on the bench and found as long as there 
is a series combination of a stepdown transform secondary (one turn), a loop 
simulator coil (approx 90uh) and a resonant capacitor, there will be 
significant current flow as the result of an outside magnetic field at the 
same frequency as the resonant frequency of these three components. (Neat to 
see how you can separate the two coils by a number of inches and still see 
good coupling!) The circuitry in the primary of the transformer has <10% 
effect on this current. My solution is to connect an optocoupler across the 
resonant capacitor and thus destroy the Q of the circuit when the the final 
is off. The opto is needed because the secondary of the transformer floats 
relative to ground. I've simulated the coupler with a couple of series 
diodes and find the magnetic coupling between loop coils drops to <1%. I 
suppose I could even use this deQing connection as the regular modulation 
method for the final, instead of switching the exciter signal on and off. 
BTW this connection should work better for the std N/S .. E/W loop 
sequencing as well.

I'll keep you posted (and others) as to the progress of the full 
modifications.

Thanks,
Bill

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