Digital Signal Processing
Many new radios employ Digital Signal Processing (DSP) to perform many functions
in software that were previously performed by electronic
circuits. Special microprocessors do the job inside the radio. The
latest generation of radios using DSP has very good performance. DSP
filtering was discussed in the preceding section.
DSP is also employed to get rid of unwanted noise. Noise reduction (NR)
is used to reduce the hissing and crackling of static and other random
noise present in the audio of received SSB and CW signals. This function
is usually available with several levels of processing, with more
aggressive levels also giving the signals a "digital" sound. Noise
blanking (NB) is used to remove repetitive noise pulses, such as those
from an automobile's ignition system or power-line noise from nearby ac
utility lines. Noise blanking is very useful in mobile HF radios and
noise reduction can be used for all SSB and CW HF operating.
DSP can also be used to create a notch filter. Not only can the filter's
notch frequency be manually adjusted, just like an electronic notch
filter, but many DSP notch filters can automatically detect the frequency
of the interfering tone and tune the notch filter (Automatic Notch Filter
or ANF). Some radios even have the ability to "notch out" more than one
tone at a time!
Radios with more DSP functions also allow you to control the filter
response; how aggressively nearby signals are rejected. A filter that
allows some of those signals to be heard has a "soft" response, while
one that rejects the signals more completely is "sharp" or "steep".
Soft filters result in more natural sounding audio, but do not reject
interfering signals as well. If the DSP functions are also applied to
the output signal, you may also be able to tailor your transmitted
audio to suit your voice, adding more average power and increasing the
intelligibility of your signal.
--- SBBSecho 3.01-Win32
* Origin: The Thunderbolt BBS - wx1der.dyndns.org (57:57/10)
|
