# Direction of a wave?

## Main Question or Discussion Point

How does one tell the direction of a wave, or is it even possible in this scenario...

"HYPOTHETICALLY"... if you have 'some sort' of electromagnetic wave and and 'some sort' of antenna, but the wave/particles travel right through your antenna, assuming your antenna still detects the wave, would you be able to determine the direction of the wave?

In other words, just like with a water wave, nothing 'actually' travels through space. The water molecules only move vertically up and down. So if you could not see the big picture and viewed only a small vertical slice of the water, you would only observe the particles moving up and down and have no idea which direction the wave was travelling. This at least what I understand and am looking for confirmation.

Thanks.

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Born2bwire
Gold Member
Antennas have a certain amount of directionality. Depending upon the structure of the antenna you could tell the direction of the incoming wave. This would work best with a highly directional antenna. Like a Yagi-Uda, parabolic dish, or an array.

Antennas have a certain amount of directionality. Depending upon the structure of the antenna you could tell the direction of the incoming wave. This would work best with a highly directional antenna. Like a Yagi-Uda, parabolic dish, or an array.
Thanks. If these are able to determine the 'path' or 'line' that the wave follows, would they be able to figure out which direction (ie, if it discovered that the wave is exactly from East to West, would it be able to tell if it was travelling toward the east or away from it?)

jtbell
Mentor
I'm one of those old-fashioned people who still gets broadcast TV via an antenna on my roof. I live in a rural area with TV stations in three different directions, and use a directional antenna with a rotator for optimum reception. When I watch the "signal strength" meter in my TV tuner while rotating the antenna, it's very obvious when the antenna is aimed towards the transmitter, versus directly away from it, or at an angle. In this picture, the transmitter is to the left, about 70 miles away.

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I'm one of those old-fashioned people who still gets broadcast TV via an antenna on my roof. I live in a rural area with TV stations in three different directions, and use a directional antenna with a rotator for optimum reception. When I watch the "signal strength" meter in my TV tuner while rotating the antenna, it's very obvious when the antenna is aimed towards the transmitter, and not away from it or at an angle.
Thanks. This is a difficult question and kind of relies on the 'hypothetic' idea that I mentioned. If the wave travels right through the antenna - which isn't the case with your experience on the roof, then, the receiver ought to pick up the signal whether pointed towards or away from the source.

That's what the example of the thin vertical slice of water was for. If we are dealing with a wave that travels right THROUGH the antenna, then the backside of the antenna ought to pick up as much of a signal as the front. The question then is, would be be able to determine the direction in that case?

Thanks.

jtbell
Mentor
If we are dealing with a wave that travels right THROUGH the antenna, then the backside of the antenna ought to pick up as much of a signal as the front.
Not necessarily. Directional antennas like mine are more sensitive in the "forward" direction than in the "backward" direction. Look at the specifications for good TV or radio antennas, and you'll find a quantity named the "front to back ratio," in decibels.

I updated my post with a picture while you were writing yours. The antennas are asymmetrical, and their "reception pattern" reflects this.

[added] Here's a page with plots showing the reception pattern of the upper antenna, as seen from the top and from the side:

http://www.hdtvprimer.com/ANTENNAS/XG91.html

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Not necessarily. Directional antennas like mine are more sensitive in the "forward" direction than in the "backward" direction. Look at the specifications for good TV or radio antennas, and you'll find a quantity named the "front to back ratio," in decibels.
Thanks. I think I might need to spend some time on rephrasing my question. I do understand that your TV antenna is directional. And yes it should be. That makes sense. I'm wondering if someone can help me with a different situation. One "unlike" the waves reaching your TV antenna. A completely different scenario that doesn't happen with your antenna where the electrmagnetic waves travel "right through" the antenna. In this scenario, direction can't be determined in the same was as your TV antenna.

...TV waves are easy to determine because all you need to do is have something block the waves on one side while detect on the other. Then when the detector is facing the source, you'll get waves. This isn't the scenario I'm looking for. In my case there is no 'blocker' - like if a ball hits you in the face - you know which direction it came from but if you feel your body temperature rising due to xrays going right through you, direction would be hard to determine.