Dear Jay, LF group,
At 06:33 14/11/2002 -0500, you wrote:
Not sure, but I think you can prove this with a small receive loop while
nulling out a local broadcast station. Tilt the loop even slightly off
vertical and away goes your null in a hurry.
Oh no it doesn't! I have tried this with an LF loop antenna - if you have
the loop horizontal, it nulls out everything from all directions, including
the QRN. It would appear there really is no vertical H field near the
ground for the loop to pick up at LF. Pity really, you could use the
horizontal loop as an omnidirectional RX antenna otherwise.
If you do this experiment with a BC band radio, and you imagine a plane
cutting through the TX and RX, so long as you keep the axis of the ferrite
rod in this plane (ie. at right angles to the H field), there will be a
null in the signal however much you tilt the axis of the rod. Try this
experiment outdoors, away from metalwork and wires which can distort the
fields and spoil the null.
If what you suggest about the TX loop antenna were true, the same is true
of an RX loop antenna. This would mean you would never get a null in
skywave DX signals with a vertical loop if they arrive at an appreciable
angle. Experience shows you usually do get a reasonable null.
Cheers, Jim Moritz
73 de M0BMU
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