"Electromagnetic radiation, this is what happens when you take charges and accelerate them".
He says that in like the first paragraph of his 'lecture'.
Nothing has to 'reverse' per se, but that is one way to get radiation. The main point being the acceleration and something that reverses direction must undergo a change in speed hence the acceleration has changed.
Something going constantly forward (never backward) can also have a change in acceleration of course just like a car on a straight road can accelerate or decelerate, but also when a car goes around a curve at constant tangential velocity it also has an angular acceleration associated with it.
So when something is going straight but changes speed it has an acceleration associated with it, and when something curves at constant speed it has an acceleration associated with it. The radiated power is proportional to the square of the acceleration so either acceleration or deceleration causes radiation.
We have to remember though that for small accelerations there will be small radiation, and for very small accelerations the radiation should be even smaller due to the squaring. Thus it should take very little extra power from the electrical power source to keep the electrons flowing.

So what are you trying to say with this video then?

 

Hello,

[The following is based on a straight wire antenna. See last paragraph for a circular antenna]

To obtain radiation from an antenna you must accelerate an electron within that antenna. What this means in terms of DC current is the current level itself must change. This is a 'double' change not just a single change. However, most applications use signals that have this property naturally because the current level itself must change in order to maintain a true AC signal.
So normal AC signals like sine waves and square waves cause radiation because the electrons are either constantly being accelerated (and decelerated) or they are done so abruptly.

This means that since a DC current does not change speed at all it can not radiate (in a straight antenna). A sine signal has constant change of change (acceleration) so it can radiate constantly. A square wave has abrupt change of change so it can radiate also.

To look at this another way, an electron at rest in an antenna does not radiate. An electron that has constant speed (velocity) also can not radiate. It's only when the electron speed changes (acceleration) does the electron radiate.
DC current in basic theory is comprised of electrons that move with constant speed, thus it does not radiate. Digging a little deeper, since the electrons are actually jumping around we might get tiny bits of radiation but the directions will be random and probably mostly cancel out although there will be noise. Since the noise is low level and uncontrollable, it is of little use in a transmitting application.

To look at this in terms of units of current, if you have a constant 1 amp flowing in an antenna there will be no useful radiation. If you suddenly change that to 2 amps, you will get radiation. If you then maintain the current at 2 amps you will not get anymore useful radiation. If you drop it back down to 1 amps you will again get useful radiation for a short time. If you do this repeatedly (1 amp then 2 amps then 1 amp, etc.) then you will get a constant stream of radiation.

Here is something to think about though...
If we have a round (circle) antenna 1 meter in diameter and pump a 1 amp DC current though it, do we get radiation?
The electrons are traveling at constant speed, however, they are also turning constantly and that means that they have angular acceleration.
My guess is that there could be radiation however it is probably very tiny because of the size of the electrons relative to the diameter of the antenna. It's like a race car riding around a track a million miles in diameter...the track looks mostly straight to the car so there is very little angular acceleration and thus in the case of the electron, very little radiation.

Regarding your question about why the electrons of a DC signal don't radiate from the wire of a circular antenna, here's the answer. The electrons in the wire are actually traveling from atom to atom as a "standing particle wave" rather than a discrete particle. If the circumference of the antenna is equal to a whole number of wavelengths, the electrons do not radiate. Keep in mind that particle waves are in femtometer range so the actual circumference of the antenna doesn't have any detectable effect on the phenomenon.

Also, if the electrons in the wire don't drop to a lower energy level, they don't radiate. This is quantum mechanics and quantum electrodynamics and the same behavior applies to superconductivity where a DC signal can produce a current for an infinite time.

 

Regarding your question about why the electrons of a DC signal don't radiate from the wire of a circular antenna, here's the answer. The electrons in the wire are actually traveling from atom to atom as a "standing particle wave" rather than a discrete particle. If the circumference of the antenna is equal to a whole number of wavelengths, the electrons do not radiate. Keep in mind that particle waves are in femtometer range so the actual circumference of the antenna doesn't have any detectable effect on the phenomenon.

Also, if the electrons in the wire don't drop to a lower energy level, they don't radiate. This is quantum mechanics and quantum electrodynamics and the same behavior applies to superconductivity where a DC signal can produce a current for an infinite time.

Hi,

Thanks for bringing this up, that was my only doubt.
However, i bring to your attention the word you used, "detectable".
I never said it would be detectable in fact i said it would be very very small. The radiation (if any) is proportional to the square of the acceleration, and as mentioned the wire circle loop diameter is very large compared to the electron and the acceleration so small and we know when we square a quantity less than 1 it gets even smaller. So we are looking at a theoretical property not so much a practical thing that can be used for anything meaningful. However, things change. Some day it may be useful, if it in fact does exist.
Another interesting point is that there are a LOT of electrons in the wire which may make a difference.

To answer for sure though i think we need to do some calculations. We might start by looking at the number of electrons in say a 1 meter radius wire loop of #18 gauge wire or something like that. IF we can prove that the signal should be detectable yet it is not, then we know it does not exist or at least not at the level we were expecting.

An extreme example would be as follows...
Take a piece of #18 AWG wire (or whatever size you like) and bend it in half so it folds over on itself with a very very sharp bend. Spread the loose ends apart a bit so that the wires dont touch either other except near the bend. Connect the two loose ends to a battery (perhaps with a series resistor to limit current).
Now we know the electrons in the straight part are moving at constant speed (although really the drift) but in the sharp bend they have to turn abruptly.
Now you think that because the electrons jump around that they wont generate any radiation even at the bend?

UPDATE LATER:
I found that the electrons do generate radiation but it is very small, possibly not measurable.
However, we also know that what is not measurable today may be measurable tomorrow.
We also know that to measure something very small that can be repeated N times means we can get N times the effect.
Therefore there may be a way to measure this effect.
It will be incredibly small though.
How can we be sure it radiates at all?
Well, if we rotate it at very high speed in a vacuum it definitely radiates. If we slow the speed down little by little we will see less and less radiation, and the effect should decrease as the square of the acceleration so it will be grossly smaller as we go down in speed. However, even something that decreases by the square still does not reach zero until we get to zero.
Again however it may be too small to measure.

Someone on Physics Forum calculated 10 amps through a 1mm wire and i think a loop of 1 meter, the radiated power would be 1e-20 watts which would be hard if not impossible to measure.
However, increasing the current may help.