[Elecraft] Question about knobs

[Richard Ferch]

Larry,

If you look closely, what happens when you tap the Width knob is that it 
changes from Shift-Width to Hi-Lo, and displays the high frequency limit 
momentarily. When you tap it again, it changes back to Shift-Width, and 
displays the width momentarily.

I think I've got this next part right: The upper and lower frequencies 
are calculated from FC +/- BW/2. When the center frequency is set to 1.5 
kHz and the bandwidth is 4.0 kHz, the calculated upper frequency is 3.5 
kHz and the calculated lower frequency is -0.5 kHz (i.e. the other side 
of zero beat). The K3's DSP imposes a low-frequency cutoff at 200 Hz, so 
although the Lo frequency may read 0.0 (it won't go negative), the 
actual lowest frequency that is passed is 0.2 kHz. Therefore, despite 
your Width setting, the actual bandwidth you hear with this combination 
is 3.3 kHz (3.5 - 0.2). What gets transmitted in turn may be different, 
depending on which roofing filter is enabled as your transmit filter 
(e.g. if it's a 2.7 kHz filter, that's an upper limit on the transmitted 
bandpass regardless of what the DSP is set to).

If, on the other hand, you use the Hi/Lo Cut settings, you can set the 
Lo to 0.2 (no point in going lower, because lower frequencies are not 
passed through the DSP anyway), and then adjust the Hi to 4.2 (that's as 
high as it will go - the DSP imposes an upper cutoff frequency of 4.2 
kHz). If you check the FC and BW by tapping those controls, you will see 
that they correspond to FC = 2.2 and BW = 4.0, exactly as the formulas 
would predict (FC = (LO+HI)/2, BW = HI-LO).

73,
Rich VE3KI


W3OZ wrote:

> I have a question about the knobs on the K3. I have my knobs on the Shift-Width \
> position. When I just push the Width knob one time it says HI 3.50 next time I press \
> the same knob again it says BW 4.00 on the display. I have the FC at *1.50. Why \
> don’t both times I press the knob say the same thing? I think from monitoring my \
> signal on Spectra Plus, that I am transmitting at about 4K but receiving at 3.50 or \
> so. Are my assumptions correct? Or why can I not have both the BWs at 4K?
>
>
> I can move the FC to 2.0 and transmit and receive at 4K, but when I try to record \
> using my DVR, the bottom end of those I record shifts up and I lose the bottom 200 to \
> 300 Hz. Not what I want to do on a faithful recording. Strange!!!! but probably \
> cockpit problems by me.