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RE: DSP fillters



In response to LU8EGB's question, I have just completed a comparison
between the DSP-9+ and the DSP-599zx in AM SWL and SSB service.  While
the 599 has many more features I found the DSP-9 to be as effective in
reducing QSB and eliminating tones in SSB.  

I purchased the 599 for use in SWL because of it's larger bandwidth. 
However, I found that the "artificial" sound due to the processing was
more annoying than the QSB.  Unlike a SSB contact, the sound quality is
important for scheduled broadcast listeners. My experience explains why
DSP units are not very popular with SWLers.  Adusting the noise
reduction agressiveness improves the sound quality, but also reduces the
effectiveness of the noise reduction.  This is not surprising given how
adaptive noise filtration functions.  

I briefly tested each unit on CW signals and both were extremely
impressive.  Reducing the filter bandwidth to 100 hz or less gives a
remarkable increase in S/N compared with my rig's standard CW filter. 

For me, a big advantage of the 599 is that it passes the rig audio when
turned off.  When you power the DSP 9 down it does NOT pass any audio. 
It does have a bypass switch as I recall however you must still use the
filter audio gain control rather than that of the rig when the DSP is
powered.  I found this inconvienient however lack of this feature alone
does not justify the difference in coat between units for my use.

In summary, my opinion is that while the 599 has many more features, the
9 is a much better value and almost as effective.  The DSP-9 is somewhat
easier to use also, just push a couple of buttons for the mode that you
desire.

Dean Shutt
AL7CR@amsat.org



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