[Elecraft] K3 - Audio/IF filtering definitions

[Don Wilhelm]

Rick,

The Hi-Cut and Lo-Cut do essentially the same thing as Width and Shift, 
but they make voice signals easier to deal with.

If you have played with Width and Shift on the K3 or other transceivers, 
you will know that anytime you change the width control, you have to 
also change the shift control to maintain intelligibility for the 
received voice signal.

The main reason is that you must have some audio content in the 300 to 
500 Hz range to have intelligibility in the human speech range. So if 
you have your Width set at 2.7kHz and the Shift set at 1500 Hz, you will 
be receiving 300 to 3000 Hz.  Now move the width to 2.1kHz and the 
passband changes to 600 to 2700 Hz, and you have lost much of the low 
frequency content of the signal - changing the Shift control to a lower 
frequency will recover that 300 to 500 Hz segment of the audio spectrum 
that is essential to communications fidelity.

OK, the Hi-Cut and LoCut controls work in a similar manner as the Width 
and Shift.  HiCut reduces the high frequency content in the received 
signal while not changing the low frequency end.  That is ideal for 
voice communications where the 300 to 500 Hz content must be preserved 
for good intelligibility.  Try an experiment - set LoCut at 300 Hz and 
then tune in an SSB signal.  Reduce HiCut until you can no longer 
understand the vocal content.  If my guess is correct, you will still be 
able to understand the voice content when HiCut is at 1500 Hz (that is a 
width of 1200 Hz).

Now try the same thing using Width and Shift - it will likely be 
cumbersome to adjust both the Shift and Width to accomplish the same 
1200 Hz width while keeping the 300 to 500 Hz content active with the 
shift control.

So the result is to use Width and Shift for CW where the center 
frequency is well defined, but on SSB (or other voice modes) the use of 
HiCut and LoCut makes things a lot easier - set LoCut somewhere between 
200 and 400 Hz and leave it there - HiCut can be reduced to remove high 
audio frequency 'garbage' as desired.  If you run into interfering 
signals on the low audio frequency range, there is not much you can do 
about it without reducing signal intelligibility (time to QSY).

73,
Don W3FPR

On 11/27/2012 5:16 PM, Rick Stealey wrote:
> I'm confused as to the function of the receive equalization vs the width vs the hi
> and low cut.
>
> Example - The traditional  SSB filter is, say, a 2.7 KHz wide filter with the
> bfo carrier 300 hz from one side of the filter passband.  This provides audio response
> of 300 hz to (300+ 2700) = 3000 Hz.
>
> So I can set my K3 to 2700 bandwidth and adjust the  SHIFT control to give the
> same response as above.  But in addition I can adjust the 8 band receive EQ to roll
> off or peak this spectrum, right?  I assume this filtering is at audio, after the detector.
>
> Then what are the hi cut and low cut front panel controls for?  What do they control?
>
> Rick   K2XT
>