MFJ-781 DSP Multimode Data Filter

摘要

The use of data modes on HF is increasing almost exponentially, not just by licensed amateurs but to a large extent by listeners as well. Fuelled by the wide availability of amateur-written programs such as JVFAX, HamComm, Mscan and the like, which use just a simple one-IC interface between the receiver and a low-specification PC (even a £5 second-hand XT type, cheaper than a second-hand Morse key!), getting going on data has never been easier. However, the user quickly finds that a strong, 'clean' received signal is needed for successful decoding, especially when using a simple data converter interface where the PC must decode the resultant signal. Although commercial stand-alone data terminal units have built-in signal filtering before the modem circuitry, the recent introduction of DSP technology, as built into modern HF transceivers, has shown that even these can benefit tremendously from prior filtering of the signal.