 There may be times when the pips will fade because of atmospheric conditions or a maneuvering target. But although they may become smaller, as long as you keep them balanced, your beam will still be on target. In order to project this split picture on the scope, the antenna, receiver and indicator circuits must be modified. Let's look at the antenna first. The antenna is designed so it can receive echoes alternately. First from the right lobe, then from the left. Notice, however, that each lobe is on long enough for a pulse to be sent out and its echo to return from maximum range before the next pulse is sent out through the other lobe. To handle the echoes from each lobe efficiently, to keep them from being mixed up, a special receiver circuit is used which acts like a gate. This gate allows signals from the left lobe to pass through and then those from the right lobe. The signals go down through the receiver alternately and onto the indicator. Hold it. That's right. Before they appear on the scope, the indicator must also be prepared to receive two echo signals and display them separately. Here's how the indicator works. When a pulse was sent out through the left lobe, at the same time part of that energy was sent over to the scope where it began forming the baseline. Thus when the echo from the left lobe returns, it forms the pip on that baseline. When the lobe was switched and the pulse went out through the right side, part of that energy was sent over to the indicator also and began forming another baseline so that when the echo from that pulse returned, it formed a pip on its own baseline. So that now you have the set sending out a pulse through one lobe, waiting for an echo, then switching to the other side, sending out another pulse, and again waiting for an echo to return before switching back again. Furthermore, the echo from each lobe appears on its own baseline. Normally, the two baselines are superimposed and appear like this, but there are still two separate baselines and two pips. On the actual scope, you may see them like this, and by adjusting your spread control, you can govern the distance between them. Okay, so now you know that by switching a single lobe back and forth often enough, we can get the effect of two lobes and thus stay on target much more accurately. So far, we've only been talking about the lobes that cover the horizontal plane and measure the azimuth of a target. But when you go looking for aircraft, you need elevation data too. So for those sets, we add another lobe, a vertical one this time, to flip back and forth and supply the angular height or elevation of a target in the same way the horizontal lobe takes care of the azimuth. Of course, the same idea holds true. Each lobe has its own pip and baseline. When the target's centered in the lobes, the pips on the elevation scope are balanced and your angular height data is correct. If the plane gains altitude, naturally it'll be in a stronger part of the upper lobe, a weaker part of the lower one, so one pip grows the other shrinks. By turning your antenna toward the larger pip, elevating it in this case, you again balance the pips and get back on target in elevation. To sum up this business on lobes, take a look at this miniature of a pip matching radar. It has two horizontal lobes, like this, for measuring azimuth and two vertical lobes for measuring elevation. Together, the four lobes make it possible for the radar beam to be centered on the target all the time, thus assuring you of highly accurate data. And of course for each pair of lobes, there is a separate scope picture. One for measuring azimuth, one for measuring elevation. This type of pip matching presentation is called the K scope. So much for measuring azimuth and elevation. You'll remember that to measure range, you need only a single pip, a scope. And the distance from the pip to the main bang represents the range of the target. As the target approaches your set, its pip approaches the main bang. The baseline or sweep, as we've said before, represents the full range of your set. When we pick up a target somewhere within that range, it's obvious that the longer the baseline we have to represent the range, the easier it will be to read our target's position accurately, right down to the last yard. However, using a horizontal baseline, this is as long as it can be and still remain on the scope. But what we can do is stretch it out three times that length and put it around the edge of the scope. With this longer baseline, representing the same range that the short one did, we can read range a lot more accurately. Here's a typical circular baseline range scope. The J scope used on the SCR 584. Now that we know why such a scope picture is desirable, let's go back to the electrostatic tube and see how we can get a circular baseline using the horizontal and vertical deflecting plates. Here's a front view of the plates. The electron beam is dead center since neither of the deflecting plates has voltage applied to it. Let's apply some and see what happens. We'll start with the deflecting plates that move the beam up and down. The sine wave represents the variation of the voltage we're going to apply with respect to time. Let's take it step by step. As the voltage climbs to this point, which we'll call A, the beam is deflected a corresponding amount toward the positive plate, upward in this case, to this point, which we'll also call A. When the voltage reaches B, its peak, the electron beam also reaches its peak on the scope, marked by B. When the voltage drops back to zero, marked by C, the beam returns to C, the center point from which it started. The same thing happens in the opposite direction. When the voltage reaches its downward peak, the beam goes down as far as it can. When the voltage returns to zero, the beam returns to center. That's one cycle of vertical deflection.