RTTY/CW filter

An appreciable part of short-wave radio traffic takes place via morse and radio teletype transmission. To ensure optimum reception of these types of transmission, a practical bandwidth of about 300 Hz is required in the receiver. Such a bandwidth allows for some drift of both transmitter and receiver, and also for the frequency shift of RTTY signals. As commercial- ly available filters meeting these requirements are still rather expensive, it pays to build your own: a suitable one is shown in the accompanying diagram. The crystals used are inexpensive types, commonly found in computer systems. Inductor L1is made by winding 2 times 20 turns enamelled copper wire of 0.3 mm diameter onto a T50/2 RF X1...X4=2.4576MHz 7-36 RTTY/CW filter L1 =2 x 20 turns enamelled copper wire of 0.3 mm dia. ontypeT50/2RFtoroid toroid (available from Cirkit). Some parameters of the filter are: ■ bandwidth at —6 dB points 300 Hz ■ bandwidth at —60 dB points 1100 Hz ■ insertion loss — 7 dB ■...