 Now let's look at the deflecting plates that move the beam horizontally. The same thing goes here. When the voltage reaches A, the beam moves horizontally to A. Every change in voltage produces a corresponding horizontal deflection of the beam toward or away from center. Next let's see what happens when sine wave voltage is applied to both sets of deflecting plates. Remember that when we apply voltage to one set of deflecting plates the electron beam is deflected upward. And if we apply the same amount of voltage to the other set of plates the beam is deflected sideways. The combined action on both sets of plates is to move the beam along this diagonal path. To simplify the diagram let's call the voltage applied to the vertical deflecting plates Y and we'll label the vertical deflecting plates Y. We'll call the voltage on the horizontal plates X and label its plates X. Now since these voltages are going to be applied simultaneously we can watch them more easily if we put one below the other. And to compare the movement of the voltages at any one instant we'll put a grid over them. Let's see what happens when voltages X and Y both reach their positive peaks together. The beam is deflected to its extreme diagonal position. That's because the vertical plates are deflecting it all the way up and the horizontal plates all the way to the side. As the two voltages complete their cycle of variation together the beam follows a diagonal path. Upwards to the left and downwards to the right. When the voltages vary together like this we say they are in phase. Now let's have everything that happens to the X voltage happen half a cycle earlier than it happens to the Y voltage. When we have this half cycle lead we say that the voltages are 180 degrees out of phase. Let's see what will happen to the electron beam under these circumstances. When voltage Y reaches its positive peak the beam is still deflected to its maximum upward position. However voltage X has reached its peak in the opposite direction causing the beam to be deflected to the right. The result is again a diagonal path but this time from upper right to lower left. Suppose that the phase shift was only half as much 90 degrees instead of 180 degrees. Notice now that at the starting point of the cycle the beam is already at its maximum left position. That's because voltage X is already at its peak while voltage Y is at zero. A quarter of a cycle later voltage Y reaches its peak and voltage X is at zero. The beam has moved through a circular path to its maximum upward deflection. As the cycle continues the beam continues on its curved path forming a circle and of course as the action picks up to its normal operating speed you get the illusion of a circular baseline. Remember that this circle is the end view of a stream of electrons. If we vary the phase shift the result will be some compromise between a circle and a diagonal line and ellipse. But phasing isn't the only thing that will affect the shape of our circle. You can have the voltages 90 degrees out of phase and still not get a circle if the amplitudes are allowed to vary. If for example the amplitude of voltage X becomes less than voltage Y it will change the circle into an ellipse pushed in on both sides because the horizontal deflection is not as great as the vertical deflection. However once you've corrected the amplitude you'll again have a perfect circle. If voltage Y is smaller you'll again get an ellipse but one which is squashed horizontally because the beam is not deflected to its maximum vertical position. If both voltages decrease in amplitude the same amount the result would again be a circle but a smaller one. When the voltage amplitudes are corrected the circle returns to its original size. So any change in the shape or size of your circle means an improper phase or amplitude adjustment. When you've corrected the amplitude and phase you'll end up with a perfect circle of the right size. Now you've seen how the deflecting plates can form a circular baseline. When this pattern is projected onto the face of your scope you get a baseline almost three times as long as the horizontal one we started with. Now that we have our circular baseline how are we going to produce pips on it? Both sets of deflecting plates remember are busy forming the baseline so something new must be added. It's a thin metallic rod inserted in the tube from the base through the center of the screen. This is the deflecting rod that will take care of forming the target pips. Here's how it works. Let's take a look at it from the front. We'll slow the beam way down so we can explain what goes on. There. That white dot is the end of the electron beam as it strikes the face of the scope. When negative voltage is applied to the deflecting rod the electron beam also negative will be repelled from the center. If we leave the negative charge on like this the beam keeps being repelled all the way around and as a result we get a bigger circle. If we remove the negative charge the beam returns to its original path. If negative voltage is applied to the deflecting rod for only an instant the beam is repelled from the center for only an instant and then comes back to normal. The timer synchronizes the deflecting voltages so that every time the electron beam is at top center the transmitter is triggered. The spill over energy picked up by the receiver and applied to the deflecting rod causes a pip to be formed. The main bang up at top center. This is zero range. The returning target echo voltage is also applied to the deflecting rod and another smaller pip will be formed somewhere on the circumference of the circle. As you can see this scope gives us everything in a scope did. A main bang, a target pip and a baseline along which you measure range. But because our new baseline is circular we can make it almost three times as long without increasing the size of the tube thereby giving us a more precise means of measuring range. Since our baseline is circular to measure range we simply put a circular range scale around the edge with zero at top center. By reading range clockwise to the pip you can tell at a glance how far away the target is. Here's that same J-scope you saw earlier. It's the coarse range scope of the SCR 584 and measures ranges out to 32,000 yards. To measure range even more accurately crank this hairline around until it's on the target pip. That makes the echo appear as an expanded pip on the fine range scope. They're at the right. It's also a J-scope and shows you an enlarged 2,000 yard segment of the set's entire range. With these two scopes you can locate a target to within a few yards. So much for the J-scope. There was still a need for another type of scope but before we get into that let's take a short break.