How did old WW2-era radars accurately measure time delay and integrate this into an oscilloscope?
The basic PPI (plan position indicator) radar display &mdash; the kind that has a bright line that sweeps around a circular screen like the second hand on a clock &mdash; works on the principle that the electronics produces the "sweep" of the electron beam in a radial path, while the signal from the radar receiver controls its intensity. Whenever a strong signal is received, a bright spot is created on the display. The position of the "blip" corresponds directly to the position of the target that created it in the real world.

Analog circuitry of that era could easily have a bandwidth of 10 MHz or more, allowing range resolution on the order of 15 meters (50 feet) or so. (Keep in mind that the signal has to make two trips, so you get twice the resolution that you might otherwise expect.) Say that the range is set to 75 km (about 45 miles). The signal will take about 0.5 ms to return to the receiver at maximum range, which means that for each pulse transmitted, the electron beam on the display must move from the center to the edge of the display in that amount of time. The circuitry to do this is no more complicated than the horizontal sweep generator of an ordinary oscilloscope. Shorter range settings require faster sweeping, but still within reason.

The output of a pulse generator could also be added to the intensity signal to create range "markers" on the display &mdash; concentric circles that gave the operator a better way to judge the distance to a target.

A sawtooth generator provides the basic sweep signal from the center to the edge of the display. There were a number of ways to get it to rotate in sync with the physical position of the antenna. The very earliest versions actually mechanically rotated the deflection coils around the neck of the CRT display. Later models used a special potentiometer that had sine and cosine functions built into it &mdash; the sweep signal (and its complement) was applied to the end terminals, the wiper was turned by a synchronous motor, and the the two taps provided the signals to the (now fixed) X and Y deflection plates. Later still, this sine/cosine modulation was done entirely electronically.

One issue was that these displays were not very bright, mainly because of the long-persistence phosphors used to produce an image that "lingered" long enough to be useful. They had to be used in a darkened room, sometimes with hoods over them that the operator could peer into. I wasn't alive during WWII, but I did do some work in the early 1980s on a chip that could digitize and "rasterize" the signal from a radar set so that it could be displayed on a conventional TV monitor. Such a monitor could be made much brighter (short-persistence phosphors) &mdash; bright enough to be used directly in the control tower of an airport, for example, so that the tower operator did not need to rely on verbal messages from a separate radar operator in another room. The chip even simulated the "slow decay" function of the analog display. Nowadays, every cheap digital oscilloscope has this "variable persistence" feature. :-)

Naturally, I had to simulate the radial scan of the analog display when writing the receiver signal into the video frame buffer. I used a ROM to convert the reported angular position of the antenna into sine/cosine values, which got fed to a pair of DDS generators to produce a sequence of X and Y memory addresses for each sweep.