But this isn't just in cameras. A transmission line has two conductors held a distance apart, so it has a capacitance as well. But it uses alternating current, so let's see what happens when we have a capacitor with an alternating current signal.
And light waves all travel at the same speed in a vacuum, about 300 million meters per second, or c. In the transmission line , the wave travels more slowly, but for a given line, that speed is still fixed, and if the speed is fixed, well, that means that frequency must be inversely proportional to wavelength.
But Smith was generating radio waves in the megahertz range, and at 10 megahertz, the wavelength is about 30 meters. With the transmission line he was working on more than two kilometers long, well, that's many times the wavelength. So, reflections were significant.
We can model the electrical signal as a simple sinusoidal voltage and current source, which we draw like this. Next is the transmission line . It consists of two conductors that form a loop.
Since both the antenna and the transmission line have their own electrical properties, we can model Smith's whole system by tying two slinkys together. One for the transmission line , and the other for the antenna. First, we're gonna try two very different slinkys.
Multiply by j again, and by definition you get negative one. a bit of extra transmission line called a stub.
They didn't think about where the power was going to go from the power plants in the transmission lines, which I have another picture for you. This is a transmission line between Baghdad and Dora. And it's very easy to bring one down.
So to have any chance of their signal reaching across the globe, Smith's team connected more than 20 smaller antennas into a massive directional array linked by over two kilometers of transmission line . Smith's job was to test this massive array, but when he tried sending a signal from the source down the line to an antenna,
But the real setup is more than just the transmission line . Since both the antenna and the transmission line have their own electrical properties, we can model Smith's whole system by tying two slinkys together. One for the transmission line , and the other for the antenna.
In electrical systems, the standing wave pattern can be a big problem. That's because if the reflections in your transmission line are bad enough, the peak voltages can reach up to twice the input voltage. And if your line isn't rated for that, well, it burns out.
Now, so far we've used just one slinky, with one set of properties, to show how waves travel. But the real setup is more than just the transmission line . Since both the antenna and the transmission line have their own electrical properties, we can model Smith's whole system by tying two slinkys together.
That's Ohm's law. The resistance is equal to the voltage divided by the current. So if a voltage wave hits the boundary between the transmission line and the antenna, and the resistance changes across that boundary, well, the whole wave can't pass through.
So perhaps this is what Smith needed to match. See, in every transmission line , there's a built-in impedance called its characteristic impedance, or Z_0. This is just a fixed property of the line.
Multiply by j again, and by definition you get negative one. We also know that as we move along our transmission line , because the same forward and reflected waves are interfering, the magnitude of the reflection
projects with uh with impoverished Indian reservations in South Dakota I had enough wind rights to power the city of Chicago but I couldn't get a transmission line built or get enough transmission capacity to get the power from the Indian reservations in The Dakotas to Chicago or Minneapolis then when I tried to sell the power I was basically blocked by a lot of coal burning power
- Here's the experiment. We've got a power source sending a radio signal down a transmission line to an antenna array, and we put it in an anechoic chamber to reduce interference. We've got a receiving antenna at the other end, which is able to pick up the signal and tell us just how much power is actually making it
That's why in circuits you might often see components that look like this. But even on a straight wire, like our transmission line , these fields still exist, and they affect the way that our current and voltage waves behave. A changing magnetic field induces a voltage that opposes any change in the current, and the faster you try to change that current,
So, how do you match a resistance without a resistor? Well, the answer actually already lies on the transmission line . When part of a wave reflects, the line now carries two waves at once, the forward one and the reflected one.
So starting from, kind of, the beginning rather. In 2014, there was a Northwest transmission line completed in British Columbia. Northwest British Columbia is an area that has about 2,000 people.
Indeed, in real life when we checked, the resistances didn't match. So the antenna array is at 12.5 ohms, and the transmission line is at 50. So, what we're gonna do is we're gonna add this 37.5 ohm or 40 ohm resistor to try to bring it up so that they match,
They all wanted the same thing, a simple graphical system that would make matching impedances quick and reliable. See, when Philip Smith tried sending a signal down his transmission line , some of the energy didn't reach the other end. It reflected, and it came bouncing straight back at him.
Multiply by j again, and by definition you get negative one. - Exactly, yeah. And hopefully as we cut this transmission line shorter and shorter, we'll move through that point.
And if your line isn't rated for that, well, it burns out. - There was a huge reflection, and a powerful standing wave did this to the inner conductor of that transmission line . This is the effect of the standing wave.
If we can match this property, it's like the discontinuity is gone and it's just one slinky again. So you might think Smith could do the same thing, except instead of matching slinkys, he had to match his transmission line to his antenna. But what electrical property could do that?
Multiply by j again, and by definition you get negative one. Now, we know to eliminate reflections, we need to match the impedance of the transmission line , and that happens when the resistance is one,
Multiply by j again, and by definition you get negative one. So instead of adding an inductor or capacitor, we get the same effect by just using a length of transmission line .
And then at the other end, allowing every employee of the company to make decisions whether or not they're in line with the CEO's vision, or allowing every community that might be impacted by the construction of a high-voltage transmission line from one place in one state to another place in another state, have a veto process.
Once the battery technology for storing solar power is good enough to be able to reliably store it, you will see local networks that are platform-based that will emerge where people who have excess power can then redistribute it to someone who needs it, either through a transmission line or by actually transporting the battery from one place to another.
a list of a few that I put down last night, room temperatures superconductors. I'll come back to this. If we had a metal that conducted electricity without any loss at room temperature, you'd have a perfect transmission line for example, and I'll come back to this one. If you could create a one penny per mile battery. Today we're talking about something that's almost 100 times more expensive.