Direct receiver
The receiver of the remote control device was a direct-amplifier at first, and its characteristic is that the high-frequency signal received from the antenna does not change its original high-frequency frequency (that is, the high-frequency signal is directly amplified) before the detection. Its disadvantage is that the high-end and low-end amplification of the receiving frequency band are not the same, and the sensitivity of the entire band is not uniform. If you want to improve the sensitivity, you must increase the number of high-frequency amplification stages, which brings difficulties in uniform tuning between all levels, and the high-frequency amplifier gain is not high, and self-excitation is easy to occur. This method is currently widely used in toys.