[Elecraft] Lack of low freq response K3 ssb rx audio

[Barry N1EU]

I made some spectrum curves of the 4KHz BW rx passband with FC of 1.00,
1.50 and 2.00 to illustrate what I'm talking about.  This list bounces
image attachments so if you're interested, please look at them here:
http://k3s.wikidot.com/

The posted curves have been verified on another K3 and RX EQ is flat.

My original question was:  Why does the audio passband dramatically roll
off in the lower frequencies as my Shift/FC goes above 1.40Khz?

I think the spectrum curves partly answer the question.  They reveal a  a
maximum passband width of 3300Hz (-3dB points) in SSB even though BW is
4000Hz,  within a 6KHz wide roofing filter.  I don't understand the
discrepancy between selected bandwidth and what the K3/K3s is providing.

For comparison, a passband curve in AM mode is also shown and it reveals
extended flat response from below 50hz to almost 4000Hz.

73, Barry N1EU


>
> On 1/31/2016 9:02 AM, Barry N1EU wrote:
>
> I'm pulling my hair out on this one, but let me keep it real simple.  This
> is on a K3s and all hardware/firmware is latest/greatest.
>
> Filter: 6KHz
> Mode: USB
> BW: 4.00KHz
>
> My question is this:
>
> *Why does the audio passband dramatically roll off in the lower frequencies
> as my Shift/FC goes above 1.40Khz?  *
>
>
> I would think that there wouldn't be any bass rolloff until FC was above
> 2.0KHz (i.e., half of 4KHz BW).  Instead, what I'm observing is:
>     - with FC of 1.6KHz, I see  -8dB at 100Hz
>     - with FC of 1.8KHz, I see -15dB at 100Hz
>
> I'm using Line Out to soundcard and Visual Analyser 2014 software.  It
> mirrors what I hear in my headphones.
>
> 73, Barry N1EU
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