[Elecraft] K3: honest question re Audio Peak Filter

[Joe Subich, W4TV]

> 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: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Barry N1EU
> Sent: Friday, January 01, 2010 7:10 AM
> To: elecraft at mailman.qth.net
> 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
Sent from the Elecraft mailing list archive at Nabble.com.
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