[Elecraft] CW filter and Roofing filter

[Don Wilhelm]

Gee,

The K3 DSP cannot be bypassed, it is part and parcel of the K3.  The DSP 
mathematical computations are what does the modulation, demodulation, 
and forms the filters as well as doing a lot of other tasks.  The K3 DSP 
processing in the K3 is done at a frequency of 15kHz.
There is no parallel to an analog receiver.  The front end of the K3 is 
analog, but as soon as the signal is converted to 15kHz, it goes through 
an ADC and becomes 'mathematical soup' - after processing, the math 
result is fed to a DAC where it emerges as audio.  In other words, the 
K3 is an SDR with an analog front end and a built-in processor.

The K3 must have the 2.7 or 2.8kHz filter installed.
If you have additional hardware filters installed, they are not cascaded 
- BUT the roofing filter can cascade with the DSP filter. Even if you 
select a narrow filter with the XFIL button, if you widen the DSP 
bandwidth beyond the width of that narrow filter, the K3 will switch to 
a wider filter.

I hope that helps your understanding.

73,
Don W3FPR

On 6/24/2015 8:55 AM, Gee wrote:
> Trying to sort this out.......
> 1) with any filter selected using the XFIL button on the K3, there is only ONE crystal IF filter in the signal path. In other words, there is no cascading or tail ending of the filters before and after the IF.
> 2) if I select a 400 Hz filter with the XFIL button then adjusting the DSP WIDTH control to any WIDER than 500 Hz is pointless.
> 3) can the DSP be bypassed to produce a purely analog demodulated audio to the speaker? As I recall years ago, some early DSP radios had this feature. I am pretty sure the answer is no but still, had to ask.
> It is interesting to note that there are new hams out there who have never listened to an analog receiver before. It can be an eye opening experience!
>