DSP filters and desired features

John W. Brosnahan broz at csn.org
Wed Aug 4 09:04:10 EDT 1993

Dear DXer and Contester Users and Potential Users of DSP filters,
(If someone could post this on any other appropriate reflectors
(other than CQ-CONTEST reflector), I would appreciate it.)
I have had a JPS NIR-10 filter since the product first came out.  I have
not yet upgraded to the latest firmware, but feel that its best feature
is the automatic removal of multiple carriers.  At Dayton this year I 
purchased a Timewave Technology DSP-59.  I was very impressed with its
automatic removal of carriers as well as its noise reduction and LP/HP
filter capability, and of its intuitive control operation, especially
the "aggressiveness of the correlation function" adjustment.
I have also been one of the beta sites for the Digital Interactive
DSP-120 filters.  Comparing it to the others is a classic apples and
oranges comparison.  The DSP-120 has digital record and playback on
the host computer (which it requires for many of its functions and
the other filters do not use a host computer), as well as a graphics 
screen display on your computer for filter selection and changing, 
and a time domain and frequency domain display.  Because of the DSP-120s 
wide range of features and computer interface it is somewhat more 
difficult to master than the other two which have only knobs and switches 
(especially in a contest on Sunday at 4 a.m. local or anytime when the QSO
rate is high).  But the DSP-120 lacks the capability of automatic reduction 
of multiple carriers that I find quite useful on phone.  (In fact my normal
operation involves leaving any DSP engine in the automatic removal mode
for all general operating.)  (When the Timewave Technology DSP-59 is switched 
to carrier removal mode and it is used on CW, its operation is so fast that 
only the leading edges of the dots and dashes get through -- very impressive.)
(The Digital Interactive DSP-120 has an adaptive filter function that when
turned on integrates the spectral components over whatever time you let it
run and designs a matched filter that corresponds to the individual's voice
to which it was listening -- impressive indeed.)
The designer of the DSP-120 is not an amateur radio operator (the filter has
a number of non-ham applications) and relys on feedback from users for adding 
and prioritizing new features.  I feel that the automatic removal of carriers 
is an important feature, maybe even a fundamental feature, and that the lack 
of this capability reduces the usefullness (and marketability) of the DSP-120.
So, I am requesting any input from both users of DSP filters as well as 
potential users regarding usefullness of various functions on the
currently available filters, as well as a "wish list" for features to
be included in the next generation of DSP filters.  Especially interested
in "correlation function" types of filtering, where highly correlated
signals (such as carriers) are rejected, low correlation signals (such
as noise) are rejected, and moderately correlated signals (such as voice)
are passed through.
Reply to me directly or via the reflector as appropriate (per Trey's
guidelines).      I am at   broz at csn.org
Thanks for the input!       John Brosnahan  W0UN

More information about the CQ-Contest mailing list