 Now, having been guided to the approximate position of the bomber, the radar operator and the night fighter can pick him up and trail him with his AI aircraft interception set. There's the target now. Let's see how these airborne radars work. Here's a diagram of our night fighter on the tail of an enemy bomber. The antenna revolves in a complete circle, but since the night fighter pilot is primarily interested in what's in front of him, only that area is presented on the scope. The rest is blanked out. This area, scanned by the beam, and of course any targets within that area, appear on the indicator or scope screen of the night fighter. A bomber that's ahead and to the right of the night fighter will appear up and to the right on the scope. Since this B-scope is intensity modulated, like the PPI you saw a while ago, the target appears as a glowing blob of light. However, the scope presentation isn't fan-shaped like the sector the beam scans, or like it would appear on the circular PPI. If it were, the short range echoes would crowd together and be hard to spot. So for ease of operation, electrical circuits actually stretch the picture into a rectangle. This is the presentation furnished by the airborne B-scope. When you turn on your AI set, this is what you'll see on the B-scope. It measures range vertically from bottom to top and azimuth horizontally. Now that we've seen the presentation, let's see how the B-scope produces this picture. Remember, with an electromagnetic tube, it's current flowing through the set of coils on the side that bend the electron beam up and down. When sawtooth voltage is sent through these side coils, we get the familiar up-and-snap-back movement, thus forming our baseline. The baseline is synchronized with the transmitted pulse, like this. When the transmitter is triggered, the electron beam starts up toward the top of the scope as the pulse goes out. When the beam reaches the top of the tube, the set's maximum range, it snaps back and starts up again with the next transmitted pulse. Since the B-scope has a persistent screen like the PPI, the repeated spillovers form a constant glow at zero range, giving you the familiar main bang. Because the pulse is transmitted hundreds of times every second, the moving electron beam whips up and down so fast that it forms the baseline. Now, when a target is caught in this beam, the returning echo from it will form a blob of light somewhere along the baseline. Zero range is at the bottom of the scope, so if the target moves faster than your night fighter, the range between the two planes increases, and the target blip will climb up the baseline toward the top of the scope, maximum range. So that you can spot the range of a target more easily, we can divide the fan-shaped sector which our antenna will sweep with imaginary range markers, for example, every mile, one to five. Then we'll calibrate the face of the tube in the same way, with the five grid lines on the scope representing the mile distances in the sky. Here, the target is almost five miles away, so its echo appears just below the fifth range marker on the scope. So much for range. For azimuth, we'll add a vertical grid with the zero marker in the center. Then, planes to the left will appear to the left of center on the scope. Those to the right will appear to the right. This target is dead ahead, so it appears on the scope at zero azimuth. But don't forget, the beam isn't stationary as we've been showing it here. It keeps sweeping through that sector, much faster than this, of course. And since the baseline is synced up with the antenna, each time the beam passes over the target, the baseline repaints the echo on the scope. Here's another target to the left at about three and a half miles, and there's its echo on the scope. There's another to the right, this time at almost two miles. Because of the persistency of the tube, the glow from each target on the screen will be visible until the baseline repaints it on the next sweep. Now let's see how the tube does all this. You've already seen how current flowing through the two side coils produced the baseline. Varying the current flowing through the top and bottom coils makes the baseline sweep across the face of the scope. The flow of current through these two coils is electrically synced with the antenna, so that the baseline always indicates the direction the antenna is pointing. Of course, since the antenna revolves at 360 rpm, the baseline on the actual scope sweeps across so fast that you can't see it, but it enables you to see the target blip that much better, because it repaints the blip so much oftener. As you can see, the B-scope is excellent for helping you find the target and determining his range and azimuth. But in order to line up your guns on him, you must know his elevation. To get that, turn on your range marker and run it up to intersect the target blip. That gates in the C-scope, there at the left. It furnishes you both elevation and azimuth. Here's how it works. To feed data to the C-scope, the antenna as it revolves also nods, that is elevates and depresses slightly. If the beam could trace its movement in the sky, the effect would look like this, painting a series of paths with each stroke a little lower than the preceding one. This is, in effect, what the stream of electrons does on the face of the scope. When the area has been covered from top to bottom, the antenna slowly elevates and the beam repaints the area from bottom to top. By moving up and down this way between the elevation limits of the set, the beam effectively scans all the space within this pyramid-shaped area in front of the night fighter. Any target flying into this area will show up in the C-scope. Let's say our target is right here. When the beam points in this particular direction, the target and echoes are reflected back. Although the antenna revolves at high speed, it moves up and down comparatively slowly, and since there are thousands of transmitted pulses per second, a good many echoes will be returned while the beam is on the target. These returning echoes will brighten a spot on the scope screen at a point that corresponds exactly to the target's position in front of the night fighter. The face of the scope is marked off with a vertical azimuth line and a horizontal elevation line. The point where they intersect is dead ahead of you. Any blips that appear above the horizontal line are from targets higher than you are. Those blips that appear below are from targets lower than you are. So the C-scope is able to give you a scaled-down picture of what you would be able to see with your own eyes if conditions permitted. For example, this enemy plane, which is to the left and below your night fighter, will show up on your C-scope as a blip to the left and below the intersection of your reference lines. To get on target in elevation, you simply maneuver your plane so the blip will come to the intersection. In this case, by turning left and diving slightly, you'll line up on your target. The addition of this clock-type mask enables the radar operator to guide the pilot in clock terms. When the blip is on the crosshairs, you know that you're on target in elevation and asthma. Keep your eye on the B-scope, and when the blip gets within gun range, open up on him. In these three pictures, you've seen how radar works in principle and have seen many of its wartime applications. The same principles apply, of course, to radar reconverted into peacetime uses. Harbor control, navigation through fog and darkness by ships on the sea. And in the air, blind aircraft landings. Weather forecasting, meteorology in which radar locates and traces approaching storms. Newfield, astronomy opened up when we made radar contact with the moon. On this sketch of the scope picture, you can see the main bang and 238,000 miles along the baseline, the echo bounced back from the moon. Here's the actual scope receiving the moon echo. With a souped-up transmitter and hypersensitive receiver, the echo from the moon appeared as a good-sized pip, 238,000 miles away.