4.4 MHz crystal filter

7-06 elektor july/august 1980 L1 : see text R L = 1K L2 =47 gH xi C2= 6 . .. 60p c3 II 5p6 L3 68 AH X2 L4 = 150 gH 11. X3 L5 65 PH xa L6 = 68 gH L7 = 47 pH g L8 =120gH X5 pE 1 I R L = 1K L When building a communication receiver one of the main problems encountered is how to obtain the high selectivity required. If an inter- channel spacing of 9 to 10 kHz (used for AM broadcasting) is maintained, an excellent filter is needed. One advantage of this type of filter is that fairly cheap crystals can be used. These are called PAL crystals and, because they are used in every (PAL) colour TV set, they can often be bought at a very reasonable price. Their only possible disadvantage is that the receiver design includes a rather outlandish crystal frequency of 4.433 618 MHz, as far as the IF is concerned. Often, however, this forms an excellent IF. The circuit diagram shows that it T2OP L9 I = 33 AH :[ Ce TP T 2P X1 ... X5 = 4433.618 kHz (PAL XTAL) 80550 7 4.4 MHz crystal filter C4 C5 C6 C7...