 High interelectrode capacitances meant that at frequencies above a few hundred kilohertz the valves lacked any usable gain and became very unstable. An introduction to radio H.J. Round made some significant developments in valve technology to try to overcome the problem. However, it was a Frenchman named Lucien Levy who opened the gate to the real solution. In 1917 he devised a system of reception which he claimed would completely eliminate 'parasites and ordinary interference'. To achieve this he used the principle of beats to convert signals from a high frequency down to a lower one where the variable filters could be made more selective. The American Edwin Armstrong later used the same basic principle in his receiver. He used a variable frequency local oscillator to convert the incoming signals down in frequency. A fixed frequency filter was then used to give the selectivity. By varying the frequency of the oscillator the receiver could be tuned from one frequency to the next. This idea had a number of advantages. Using a low frequency for the filter gave better selectivity, and by keeping its frequency fixed, several stages could be placed in series to give even better performance. He also included a significant amount of amplification at this lower intermediate frequency stage, where better gain could be achieved from the valves. Armstrong patented his idea for the receiver, he called a supersonic heterodyne, or superhet receiver, on 30 December 1918. It was too late to see any real use in the war and the superhet did not see much use for a number of years. The main reason for this was that they used more valves than their regenerative counterparts, and for normal broadcast reception the additional performance was not needed. At this time most long-distance communications were undertaken on very long wavelengths. As a result amateur experiments were relegated to the short wave bands with wavelengths shorter than 200 metres. These bands were thought to be of little use, but undeterred by this, radio amateurs