As far as the professional manufacturers are concerned, the direct (TRF) receiver has "played out his tune". After half-century struggle on the market, it has been replaced by the superheterodyne receiver, that was patented in 1918 by Edwin Armstrong. In that time, commercially speaking, its main advantage was its substantially easier tuning to the station. It requires only one button for this, comparing to the TRF receiver that needs two buttons to be intermittently adjusted for optimal reception, and also it requires much of the knowledge, skill and patience, which the average buyer does not have. The superheterodyne receiver is, however, also more complex than the TRF, and setting of its stages during its production requires some special instruments, that the average radio amateur does not possess. Nevertheless, it is not impossible to build such device in the amateur environment, and when the operating principles are known, the necessary adjustments can be done "by hearing".