The Decca/Plessy 424, wavelength 3cm and scanner rotation of 20 odd RPM [forgotten the exact RPM...... long time ago!], excellent renewal of information enabled accurate presentation of aircraft position. The Plessey 430 with a capable scan rate of 44 RPM...... even better! The problem with the short wavelengths being the susceptibility to weather interference.
A minor correction, Helen - probably a typo - the higher rotation rate of the 430 was 40 rpm, in theory to cater for high speed aircraft on final, but in practice a useless facility as it tended to shake the console and the aerial apart. It was also self defeating as it limited the number of strikes on each rotation which was not good as it was a poor enough piece of kit anyway! Other factors not mentioned that contributed to its approval for 0.5 nm RTR were the short pulse length and narrow beam width which ensured accuracy - even if it did require considerable imagination to maintain the identification!
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