K3: honest question re Audio Peak Filter

[Barry N1EU]

Vic, I think you might have missed my second post where I draw a
similar conclusion:

http://mailman.qth.net/pipermail/elecraft/2009-December/122275.html

73/HNY,
Barry N1EU

On Fri, Jan 1, 2010 at 1:28 AM, Vic K2VCO <[hidden email]> wrote:
> But is this any different from reducing the K3 DSP bandwidth to 50Hz and
> turning up the volume?
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[Julian, G4ILO]

This is all very interesting, but I seem to recall a post a few days ago by Lyle stating that the K3 RX EQ was applied by additional shaping of the IF response, and there is no programmable filtering at AF in the K3. That is the reason for the LPF board.

So surely this is one wish that can only be fulfilled using an external box, unless Elecraft finds a way to shoehorn a new APF board into the K3?

[Barry N1EU]

As far as I can see, Lyle's dsp firmware is creating the AF response dynamically from the IF - it's just a matter of Lyle shoehorning APF code.

I'd guess that one reason LPF was implemented in hardware rather than firmware is to filter out noise that was generated either at the DAC or post-DAC.

73/HNY,
Barry N1EU

 

Julian, G4ILO wrote

This is all very interesting, but I seem to recall a post a few days ago by Lyle stating that the K3 RX EQ was applied by additional shaping of the IF response, and there is no programmable filtering at AF in the K3. That is the reason for the LPF board.

So surely this is one wish that can only be fulfilled using an external box, unless Elecraft finds a way to shoehorn a new APF board into the K3?

[Joe Subich, W4TV-4]

> I'd guess that one reason LPF was implemented in hardware
> rather than firmware is to filter out noise that was
> generated either at the DAC or post-DAC.

The LPF eliminates leakage of the DAC clock and audio IMD
products of the clock with the recovered audio.  Those
products are not within the control of the DSP code, they
are hardware issues.  

The DAC clock/IMD is only an issue in the K3 because the
receiver is so quiet above 4.5 to 5 KHz.  Where other rigs
have audio response (noise floor) that is roughly 50 - 60
dB below the peak audio output, the K3's out of band audio
is down more than 90 dB (!) at 5 KHz except for the DAC
artifacts.  Even though the artifacts are more than 60 dB
below peak audio, they are more than 30 dB higher than the
receiver noise floor (at the same frequency) and are easily
audible for those with normal hearing and good speakers or
headphones.

I've ordered a pair of the LPF boards and will make comparisons
between S/N 622 with none of the audio modifications and S/N
1450 with all of the modifications except the LF audio
enhancement once I've installed the LFP in 1450 (and before I
do the updates to s/n 622).

73,

   ... Joe, W4TV
 

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Barry N1EU
> Sent: Friday, January 01, 2010 7:10 AM
> To: [hidden email]
> Subject: Re: [Elecraft] K3: honest question re Audio Peak Filter
>
>
>
> As far as I can see, Lyle's dsp firmware is creating the AF
> response dynamically from the IF - it's just a matter of Lyle
> shoehorning APF code.
>
> I'd guess that one reason LPF was implemented in hardware
> rather than firmware is to filter out noise that was
> generated either at the DAC or post-DAC.
>
> 73/HNY,
> Barry N1EU
>
>  
>
> Julian, G4ILO wrote:
> >
> > This is all very interesting, but I seem to recall a post a
> few days
> > ago by Lyle stating that the K3 RX EQ was applied by additional
> > shaping of the IF response, and there is no programmable
> filtering at
> > AF in the K3. That is the reason for the LPF board.
> >
> > So surely this is one wish that can only be fulfilled using an
> > external box, unless Elecraft finds a way to shoehorn a new
> APF board
> > into the K3?
> >
>
> --
> View this message in context:
> http://n2.nabble.com/K3-honest-question-re-Audio-Peak-Filter-t

p4237359p4239351.html
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