mini signal cleaner - FSK filter for computers

FSK filter for computers A problem well known to personal computer users is the difficulty of swapping cassette tapes containing software. One of the main reasons for this is the setting of the read/write head in the cassette recorder. This should be at 90° with respect to the tape but in practice this is not always the case, with the result that loading a program from a "strange" tape causes problems. When using FSK (Frequency Shift Keying) the signal cleaner here pro- vides a very marked improvement. The time spent searching for the cor- rect signal level is then greatly re- duced. As the filter requires only five components there should be no problem finding a space for it within the case of any computer. The layout of the circuit is not at all complex. The signal passes first through the low-pass filter, consisting of R1 and C2, which has a cut-off frequency of about 1600 Hz. In fre- quency shift keying a "0" or "1" is recorded on the tape as a sinusoidal signal (with frequen...