121.5/243 MHz emergency receiver concept

摘要

121.5/243 MHz emergency receivers are permanent components of aircraft radio facilities. The RF section of an emergency radio receiver concept is described which reduces the technical expenditure and thus allows the further miniaturisation of emergency radio receivers, for example in thickfilm technology. A single IF at low frequency, for example 455 kHz, is provided. To obtain adequate image rejection for this, high attenuation is required at the RF input for the image rejection. According to the invention, this is achieved by crystal filters at the input frequency preceding the mixing stage. The essential savings are based on - absence of double frequency conversion, as a result - no problems with spurious receiving locations, - low power consumption because of the low single IF and omission of a double IF, - size advantage of crystal filters compared with large-size RF input coils with a high Q.