When British government censors first read a radar patent that the
electronics company Marconi filed in 1982, they immediately slapped a secrecy
order on it. After 18 years, the government now thinks it is safe to reveal
details (GB 2 341 994). Radar can produce false readings when, for example, the
signal is reflected by more than one surface. Marconi鈥檚 engineers analysed the
spurious signals and found that they only lasted a few milliseconds.
In Marconi鈥檚 patent, reflected radar signals are delayed for a fraction of a
second to allow pulses of less than 1.5 milliseconds to be filtered out.
Although the invention hides very rapid changes in a flight path from the
radar鈥檚 user, it makes the data more reliable.
