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Originally Posted by Nisgeis
Luke, the current SD radar in game rotates and gives range information on the same bearing as the SJ is pointing, you're saying that's not how it worked IRL. So IRL, was the SD radar an active device, e.g. it sent out an omnidirectional wave and then displayed at what range it received a signal back?
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SD radar does not give range information on the same bearing as the SJ radar. It takes SD radar one second to do a full "sweep," but no, it does not revolve (SJ radar rotates at 6 revolutions per minute, I believe). That one-second sweep is the time it takes for the antenna to send out and receive back a return on its signal, giving a range to the target if it found anything.
The first SD radar sets had what is known as a vertically polarized antenna, which did not allow for that far of a range or that low of an altitude. With the following (practically identical) SD-a and SD-1 radar sets ("improved SD radar" in SH4), the antenna switched to a horizontally polarized one, thus allowing increased range (about 15 miles max) and better low altitude performance, though it couldn't pick up anything below 1,000 feet. Contrary to initial reports, the Japanese could and did pick up on the signals the SD radar put out, hence why the standing order was to use it at irregular intervals. SD-a was the field modification of SD; SD-1 was the factory-produced version; a further version, SD-2, was practically the same, other than having the addition of IFF.
BTW, there's a good set of articles about those polarized antennas at Wikipedia and why they work like they do.