Iowa displays her radars, including air-search, surface-search and several kinds of fire-control In the past few decades, longer wavelengths have also proven useful at detecting stealthy aircraft, which are usually optimized against the shorter wavelengths used on land. In general, this affects short-wavelength radars more than long-wavelength ones, although radars with longer wavelengths have trouble seeing close to the horizon.
Because these paths are different lengths, the waves can reinforce or cancel each other out, creating a complicated pattern of zones where the signal strength can either climb or drop, depending on the various paths the signals take. A calm sea is a good reflector of radio waves, which means that there are multiple paths that a radar signal can take to and from the target. But other effects tend to limit naval use of the shortest wavelengths in certain applications. First and foremost, waves shorter than about 7.5 millimeters are heavily absorbed by water vapor, to the point that they are useless for long-range detection even on land, to say nothing of operations at sea. This didn't make it impossible to use radar data to build a picture, as the British did with the Chain Home radar feeding information to the Dowding system, but this took lots of manpower and organization.īut if shorter wavelengths are better, why do the latest warships carry radars using wavelengths fairly close to those carried by Iowa in 1945? There are several reasons for this. Checking different bearings required rotating the antenna, often manually, and left the operator with the job of keeping track of what was going on around him. This gave the operator precise knowledge of ranges, a vast improvement over previous methods, but only in the direction the antenna was pointing. An object reflecting the beam would appear as a spike or trough on the line, depending on how the A-scope was set up. Essentially, the A-scope would draw a horizontal line for each pulse, deflected up (or down) depending on the received signal strength at a given range as measured by the round trip speed-of-light delay. 2 The returned signal would be displayed using a device known as an A-scope, a special cathode ray tube. A transmitter would send out a short pulse through an antenna shaped to focus the signal in a particular direction, and then switch over to listening for the echos through the same antenna.
The first radars, as developed in the late 1930s, were extremely crude. The first USN at-sea radar test aboard the USS Leary, 1937
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