http://elecraft.85.s1.nabble.com/K3-and-AM-mode-using-the-DSP-bandwidth-controls-tp457125p457127.html
To clarify -- Will something equivalent to this mode be possible on the K3
> I'm sure my fogginess on this is due to my own understanding deficit,
> but I would like some more explanation on this in order to compare
> how the K3 will be used to how I use GC receivers now to listen to AM
> SWBC in congested bands.
> I've found the best way to reduce QRM while using a typical "dumb"
> AM/SSB GC receiver is to put the carrier in the center of the IF
> passband, then switch to either USB or LSB mode (with the carrier
> zero-beat) and listen to either the upper or the lower sideband. That
> way, if adjacent-channel QRM is worse on the high side, listening
> only to the lower sideband eliminates it, and vice-versa.
>
> Will something equivalent to this mode of reception be possible on
> the K3?
> Bill / W5WVO
>
>
> wayne burdick wrote:
>> A few of you have asked how to use and interpret the settings of the
>> receiver's DSP controls when in AM mode (SHIFT/WIDTH and HICUT/LOCUT
>> functions). I'll be improving the associated Owner's Manual section
>> soon, but I thought I'd try to get the word out more quickly.
>>
>> What the DSP controls are adjusting is the final audio passband: what
>> you hear. This is true in all modes, and is immediately reflected in
>> the DSP "graphic" on the LCD. When you rotate WIDTH and see "2.80",
>> that means that the audio bandwidth is 2.80 kHz. When you rotate
>> SHIFT and see "1.60", that means the center of the audio passband is
>> 1.60 kHz.
>>
>> Of course there isn't just audio filtering in the K3. As you rotate
>> these controls, we internally adjust the 1st and 2nd I.F. passbands
>> optimally to match the audio passband. For example, in SSB mode, if
>> you set WIDTH to "2.80", and have a 2.80 kHz crystal filter, then you
>> have three filters all cascaded at this same bandwidth: a 2.8 kHz
>> 1st-IF crystal filter (centered at 8.215 MHz); a 2.8 kHz 2nd-IF DSP
>> filter (centered at 15 kHz); and finally, a 2.8 kHz DSP audio filter
>> (centered at 1.6 kHz). We do all the math to make this as seamless as
>> possible, selecting the ideal crystal filter as you cut the highs or
>> lows or reduce the audio bandwidth.
>>
>> With this in mind, I can now explain what happens in AM mode, which
>> has to be handled differently.
>>
>> An AM signal is comprised of a carrier and both sidebands. So it's
>> much wider than an SSB signal, and this is why you need a 6-kHz
>> crystal filter for best fidelity. But this filter bandwidth is only
>> required ahead of the AM demodulator, that is, at the first and
>> second I.F.s. After the demodulator, we're back to the audio passband
>> -- what you hear.
>>
>> So, when you rotate the DSP controls in AM mode, even though you'll
>> typically see the 6-kHz filter selected ("FL1" on my rig), you won't
>> see "6.00" shown on the LCD. Instead, you'll see the audio bandwidth
>> ("2.80", etc.), just like you do in other modes. And this is what
>> makes sense, given that the controls are linked the AF passband.
>>
>> This will be even more apparent when using FM (coming soon!). FM
>> requires a filter around 13 kHz wide. As you can see, having the DSP
>> controls show something like "13.00" when WIDTH is rotated wouldn't
>> be very useful. You'll want to know how they affect what you hear,
>> not the underlying IF filter selection.
>>
>> Note: For now, I suggest that you enable only the 6-kHz crystal
>> filter for AM. A future firmware revision will also properly handle
>> the 2.8 or 2.7 kHz crystal filters when DSP controls are rotated in AM
>> mode.
>> This will be most useful when doing hicut/locut.
>>
>> 73,
>> Wayne
>> N6KR
>>
>>
>> ---
>>
>>
http://www.elecraft.com>>
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