Jim,
There is always the 2.7 (or 2.8) kHz roofing filter in-line even if you
have no other roofing filters.
If your situation is such that you do not encounter strong stations
within that 2.7 kHz bandpass, you can do just fine with only that
filter, the DSP is quite capable of isolating a single signal with no
problem.
The "problem" comes in if you have strong signals (S-9 +40 or more) near
the frequency you are trying to receive.
Those strong signals will activate the Hardware AGC and will cause AGC
"pumping" - meaning that the signal you are trying to copy will appear
to go up and down in strength. What is really happening is that the
strong signals within the passband of the 2.7 kHz filter are activating
the K3S hardware AGC and reducing the receiver sensitivity to keep that
strong signal from overloading the ADC. You may not even hear that
strong signal because it is outside the DSP filter bandpass.
In other words, if you experience problems with the desired signal
strength going up and down, then that strong nearby signal that you
cannot hear may be to blame. A narrow roofing filter will not allow
that strong signal into its passband and is a benefit during contesting
(or DXing in crowded conditions.
This was discussed at length in the early days of the K3. In this
aspect, the K3S is no different than the K3.
73,
Don W3FPR
On 11/11/2015 6:00 PM, James Rodenkirch wrote:
Anyone using the K3S in cw with no roofing filter(s) and enjoying how it sounds
during a contest?
Does the DSP filtering and the audio peaking filter do the job for you without
a 500 hz roofing filter?
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