[Elecraft] [K3] K3 Receiver Noise Level -- Evaluation and Adjustment

[Sverre Holm (LA3ZA)]

Concerning the last few days' discussion of noise and artifacts, here is a
spectral analysis plot of my K3's output:
http://www.qslnet.de/member/la3za/bilder/K3-CW-spectran.jpg

First it shows the signal related artifacts in the 10-13 kHz range as
mentioned by Wayne N6KR below. It also shows line noise at approximately
every kHz (harmonics of 1.025-1.030 kHz). The highest of these is at approx
2050 kHz and is at about -40 dB relative to the main signal, i.e. at a level
of about 10^(-40/20) = 0.01 or 1%. Thus these lines could be audible and be
part of the explanation for the complaints about the K3's sound. Apart from
the lines, the background is down to -60 dB above 2-3 kHz.

It is interesting to note that my spectran plot has discrete line noise as
opposed to that of G4ILO in his blog from today
(http://www.g4ilo.com/blog.html), plot here:
http://www.g4ilo.com/uploaded_images/k3freqresponse-736797.gif . His
background noise level is similar to mine. 

Could this be due to differences in individual K3's as has been hinted to on
this list?

My setup is:
K3 with PRE on at 14.102 MHz, RF gain at max,
CW with 400 Hz roofing filter and bandwidth set to 400 Hz,
AGC-F on and with AGC parameters SLP=9, THR=3,
I use a lot of averaging in Spectran to make the lines more visible as seen
from the setup info in my plot


wayne burdick wrote:
> 
> This filter rolls off everything at about 4.5  
> kHz, including some low-level AF sampling artifacts from 10-14 kHz  
> that some operators with excellent ears can hear. 
> 


-----
Sverre, LA3ZA

http://www.qslnet.de/member/la3za/K2/mod.html LA3ZA Unofficial Guide to K2
modifications 
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