Ken makes a pertinent comment; "the DSP does all the rest". Suggested
filters are roofing filters and serve a function of signal path and how
signals outside of the DSP bandwidth can affect the receive
performance. Receiver selectivity is actually accomplished by the DSP
engine. Regarding the function of roofing filters, I suggest reading
material such as:
http://www.sherweng.com/documents/NC0B-Contest-U-2008-9.pdf Although a
slide presentation, the information is clearly definable and explains
the use and the application of roofing filters.
If one is not anticipating CW contest operation nor has a station nearby
physically that would be on the same band at the same time, then it is a
good likelihood that no additional filter is required. As some have
pointed out, understand that operationally the roofing filter is
selected based on the DSP bandwidth selection. If one chooses to
operate CW with a 500 Hz DSP BW, the 400 Hz roofing filter would not be
in the signal path. Changing the DSP BW to 400 Hz or less will switch
the 400 Hz roofing filter into the signal path. This would then make it
more understandable why a very narrow roofing filter might not be
advisable unless the need actually exists.
Every one has their personal preferences based on their specific
operation, physical location and proximity to other stations operating
on the same band and a host of other effects. In my case, I choose the
6.0 kHz filter because I do operate some AM, the standard 2.7 kHz
filter, the optional 1.8 kHz filter for SSB and the 500 Hz filter for
digital modes and CW. In another of my radios I do have a 300 Hz
roofing filter. I find reducing the DSP bandwidth to 300 Hz to allow
this filter to be selected is typically too tight for my operating
preferences.
73
Bob, K4TAX
K3S s/n 10,163
On 9/28/2015 10:53 AM, Kenneth Christiansen wrote:
Hi to the Gang
This is a subjective question but after using a 500 hz and 200 hz filter for 7
years I ordered a 400 filter for my K3s. The main reason is it works well for
both CW and RTTY and of course the DSP does all the rest. I also ordered a 2.1
khz filter so if I go past 400 hz I get that one. It works well for me but this
is just my opinion.
Ken W0CZ w0cz at i29 dot net
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