[Elecraft] : K3 receiver noise - my test results (long)

[Julian, G4ILO]

Don Wilhelm-4 wrote:
> 
> My conclusions: I am not certain what K3 owners are perceiving as noise 
> any more than I  had been before these tests.   The flatter passband of 
> the K3 may be sub-consciously perceived as being more 'harsh', but I 
> could not equate that to 'noise'.  The other filters with a high end 
> in-passband response that drops off similar to a "pink noise" response 
> *could* be causing a perception of additional noise *if* their local 
> noise has significant content in the 2 kHz to 3 kHz range - yes, the K3 
> will make this section of the audio spectrum louder than the other 
> receiver I measured.  The "audio hiss" is not coming from the high 
> frequency spectrum outside the passband because in that area, the K3 and 
> the K2 are much more quiet than the others measured.
> 

I used Spectran rather than Spectrogram which has the advantage that it can
also be used interactively as an audio filter. I found that decreasing the
bass content by increasing the frequency of the high pass filter made the
audio seem more noisy. I presume this is because high frequency noise
components then comprised a greater proportion of the signal and were
emphasized.

I think that if people were using low impedance headphones and the original
DSP board with small value coupling capacitors then they would find the
audio over-bright and harsh, as I did.

I tried different AGC settings and agree that lower AGC THR settings make
the radio sound more noisy, so that may also be a factor. I am now using AGC
THR = 8 which is the maximum and might well use a higher setting if it was
available. I am also using AGC SLP = 1.

Having identified the problems and made some adjustments to settings the K3
sounds really good now on high impedance phones and on the internal speaker.

-----
Julian, G4ILO. K2 #392  K3 #222.
* G4ILO's Shack - http://www.g4ilo.com
* KComm - http://www.g4ilo.com/kcomm.html
* KTune - http://www.g4ilo.com/ktune.html

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