Hi Tony, With the 455Khz IF version, exactly what is the crystal frequency? I ask this as the IF is usually a lot narrower than the direct receive varieties and it would be preferential if it was to one side so that one does not have the potential problems around the centre frequency. A 1.820Mhz xtal centres the bandwidth yet a 1.780 or 1.860 Mhz xtal would provide the offset to give the 20Khz coverage outside the "zero" point.
Or have I missed something? Peter
