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Averagesupernova said:The antenna is being fed by AC so why are you concerned with direction? Think of it as electrons bunching up on one end and then running back to the opposite end over and over. I would say the diagram is correct. It is a snapshot in time though, not a steady state representation.
erece said:i am just concerned with the direction. I think current flows outwards from the positive terminal of the source. But in the figure it is opposite.
samski said:could be talking about electron flow rather than conventional current...
erece said:But according to the polarity shown , is the current flow direction correct ?
In the next cycle , the polarity of the source will change and the direction changes as well.
I have seen this same diagram in so many tutorials.
Averagesupernova said:The diagram is correct. If the antenna is actually radiating, the current has to flow the same direction on BOTH sides of the feed line. Could the antenna be fed if the current was flowing in opposite directions? Think about the current in the feedline. You are correct in saying that in the next cycle everything changes around.
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As I stated in a previous post, and yes I'm sure sophie is cussing me at this moment for bringing those little devils into this, think of it as electrons bunching up on one end and then running back to the opposite end over and over.
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It is easier for me to envision it like this: Think of a skate board ramp. The skater is an electron. The skater runs back and forth from side to side with max velocity in the middle (lowest point) of the ramp and least velocity at each side (highest point) of the ramp. Never do max velocity and highest elevation both occur at the same point on the ramp. The skaters direction changes every time he hits the top of the ramp the same way the current polarity changes with each cycle. I know there are people on here that HATE analogies, but I think it may help you. Velocity and direction of the skater represents the magnitude and direction of the current. Don't confuse this with velocity of current. No analogy is perfect of course.
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The analogy does work for feeding the antenna as well. Think about where the skater gets his extra push to continue oscillating. If he were to get his push in the middle, which is a low impedance point on a dipole, he has to be pushed with max velocity which in the anology represents max current (lowest impedance). If he gets it towards the top it is the opposite.
erece said:great explanations...
I got it...thank you all.
One more question
I read this somewhere for current and voltage distribution that voltage will be minimum at center where current is maximum. How can it be possible for the voltage to be minimum at center? May be i read wrong
Averagesupernova said:I don't really know what to say here sophie. I already admitted no analogy is perfect. You question: ...how do explain that the current further out gets less? Well I don't. I stated, this is the third time now I believe, that no analogy is perfect. Get over it already, and I'm taking the liberty of remembering your acceptance of analogies from previous threads. If there is an explanation in this analogy it is that the current is represented by the velocity of the skater. And I already said DON'T CONFUSE THE VELOCITY OF THE SKATER WITH THE VELOCITY OF THE CURRENT!
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You are correct in saying that electrons are not a free pass to understanding. Anyone who believes that has never probably done much with electronics. It is a matter of how far down you want to go. As far as most residential elecricians are concerned the wiring they install just as well be carrying invisible marbles. But if you are in the business of designing semiconductors it is unlikely you will be thinking of invisible marbles hopping between PN junctions.
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From what I take from the OP in this case is that they don't understand how the current can be the same polarity over the length of the antenna and the voltage not be. I thought I explained how that is possible pretty well.
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Edit: Looks like the OP got it, hmmmm...
Averagesupernova said:It is correct that the current is max at the center and voltage is at minimum. You read correct.
erece said:great explanations...
I got it...thank you all.
One more question
I read this somewhere for current and voltage distribution that voltage will be minimum at center where current is maximum. How can it be possible for the voltage to be minimum at center? May be i read wrong
yungman said:It is not true, it all depend on the length of the dipole as shown in my equations. Books claimed it is too difficult to get the exact expression of the current, so they approximate using phasors with open termination at the end as show in my first post. The equation specified for the length h compare to quarter wave that if h> quarter wave, the max is somewhere in the line, not at the end due to sum of the forward and reverse voltage phasor.
yungman said:It is not true, it all depend on the length of the dipole as shown in my equations. Books claimed it is too difficult to get the exact expression of the current, so they approximate using phasors with open termination at the end as show in my first post. The equation specified for the length h compare to quarter wave that if h> quarter wave, the max is somewhere in the line, not at the end due to sum of the forward and reverse voltage phasor.
sophiecentaur said:But it's true for up to and a bit beyond a half wavelength dipole and particularly for the dipole shown in the original diagram. Yes, you can arrange for a high drive-point impedance if you make the dipole still longer or if you drive it at a point not at its middle. That just adds complication I think. The exact current distribution is very difficult and the 'end effect' is also there to upset the voltage distribution. I'll bet all that wasn't included in your first introduction to antenna theory!
The current in a dipole antenna flows back and forth along the length of the antenna, creating an electromagnetic field that radiates outward into space.
The current direction in a dipole antenna is determined by the direction of the alternating current flowing through the antenna's conductors.
The current direction in a dipole antenna is important because it determines the direction of the electromagnetic radiation pattern, which affects the antenna's ability to transmit and receive signals in a specific direction.
Yes, the current direction in a dipole antenna can be changed by altering the orientation of the antenna or by using additional elements such as reflectors or directors to manipulate the radiation pattern.
The current direction in a dipole antenna directly affects its gain, as the direction of the current determines the direction of the strongest radiation. By optimizing the current direction, the gain of the antenna can be increased in a desired direction.