[Elecraft] K3S query

[Don Wilhelm]

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?
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> Does the DSP filtering and the audio peaking filter do the job for you without a 500 hz roofing filter?
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