Re: Can a loop be shielded from one side? -FARMERIK


Tony Germanotta
 

The problem with steering loops is they only respond to the magnetic component of a radio wave not the electrical one that a wire or rod uses. 

I think it’s pretty difficult to block the magnetic component. You can use phase cancelling to steer the reception pattern. It doesn’t block the signal, it matches the undesired one with a completely out of phase version. Get the two to exactly the same strength and the bad one disappears. Mark Connolly has done a lot of amazing work on phasing and steering loops. But it sure isn’t as simple as putting a metal shield behind the loop. 

You can also do something similar by using more than one loop in an array. The distance between loops and the way you angle them can favor a certain direction. 

The rock cliffs probably work well on sky wave propagation, such as Trans Pacific signals. Might not do so well blocking Ground Wave signals that tend to travel along the earth. 

A beverage antenna uses the resistor connection to its ground rod to eliminate signals off the back end. 

On Oct 6, 2018, at 12:36 PM, Andy ai.egrps@... [ultralightdx] <ultralightdx@...> wrote:

 

farmerik wrote:

    "I am curious if any one has simply shielded one directional  pattern to hear only the other? "

I think you are talking about a reflector -- not a shield.  You may have a misconception about a shield (as in "shielded" antenna).

Things like "shielded" loop antennas are not really shielded, though they might make use of the shield as part of the antenna itself.  There's a misconception that the coax shield when coax is used to make a loop antenna, somehow shields the antenna from picking up the electrical field.  It doesn't   But it does help balance the antenna, which can be good for noise rejection.

But anyway, if you put a loop antenna on one side of a large metal plate, or metal screen, it would tend to block signals arriving from that direction, from reaching the antenna -- in the same way that the "reflector" element of a Yagi or boom antenna does.

Regards,
Andy


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