[Lowfer] Jay's K9AY ANT

[JD]

>>> My own suggestion is a directionally coupled pick up.....see waveguide 
>>> and coax (trough-line ) directional couplers. The terminating resistor 
>>> gives the "directionality". >>>

Alan, this is a very good analogy.  In fact, closer than an analogy.

The usual K9AY loop is way too small to qualify as any type of wave antenna. 
It can't achieve directionality through the traveling wave effect alone. 
And, a wave antenna requires almost no elevation above the earth in terms of 
a wavelength.  The K9AY loop does need some.

If the far end were shorted to a return path, it would be a plain loop and 
exhibit the usual bi-directional pattern of a loop.  If the far end were not 
terminated at all, it would simply be a random wire antenna with a 
substantially omnidirectional pattern.  What happens if you combine signals 
captured with these two patterns in approximately equal voltage ratios?  The 
result is a pattern that strongly favors one direction over the other!

Now, I recall that this explanation for the K9AY operation has been 
pooh-poohed on this reflector in the past.  But it IS exactly what happens 
in a directional pickup in a transmission line.  The pickup loop couples to 
its output a non directional sample of voltage at that point in the line, 
without regard to the direction of power travel.  The pickup loop also 
magnetically samples the current flow in a bidrectional manner.  The 
terminating resistor and the impedance of the load "viewing" the sample 
comprise part of a bridge with the loop, combining the two samples to 
achieve the wanted directional sensitivity.

I can see no electrical difference between a K9AY loop and a reflectometer 
pickup except for the fact that the antenna is coupling to a wave in free 
space rather than in a confined line.

John

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