Posted by
Joe Subich, W4TV-4 on
Dec 20, 2009; 5:47pm
URL: http://elecraft.85.s1.nabble.com/K3-Receiver-Noise-Level-Evaluation-and-Adjustment-tp4187070p4195360.html
> However - and this is the interesting bit - the level of the
> harmonics relative to the fundamental can be varied by
> changing the LIN OUT level. On my K3 reducing LIN OUT to 003
> and they just about disappear. (Obviously that also depends
> on the strength of the input signal.)
Using Line Out is not a good representation of the audio response
to either the speaker or headphones. The Line output originates
in a different DAC (U29) than the headphone and speaker output
(U7). In addition, the differences in amplifiers, LM4950 for
the speakers and LM4811 for the headphones really means that one
must measure the specific output with the appropriate loading
(speaker or headphones) in place.
I see that Paul has already answered the low level linearity issue
with the Line output. Note as well, the transformer issue also
results in significant LF roll off starting at 1 KHz if R19 and R20
have not been changed on the KIO3 board.
73,
... Joe, W4TV
> -----Original Message-----
> From:
[hidden email]
> [mailto:
[hidden email]] On Behalf Of Julian, G4ILO
> Sent: Sunday, December 20, 2009 11:59 AM
> To:
[hidden email]
> Subject: Re: [Elecraft] [K3] K3 Receiver Noise Level --
> Evaluation and Adjustment
>
>
>
>
>
> John Lemay wrote:
> >
> > I have deviated from white or pink noise, because most of
> the time we
> > are listening to real signals (or qrm!). I decided to
> inject a signal:
> > I used my K3 and XG1 to perform the test. The line out from
> the K3 was
> > connected to line in on my PC.
> >
> > With reference to a fundamental audio signal at 0db, a
> third harmonic
> > of this was observed at about -40, and a fifth harmonic at around
> > -50dB. The even order harmonics are well down in comparison.
> >
>
> Hi John.
>
> Thanks for posting this. It reminded me while I had Spectran
> set up to take a look at something that has often bugged me -
> the appearance of harmonically related ghost signals when
> using narrow filters in CW or PSK31. I used the XG1 as you
> did. With a wide bandwidth selected, the harmonics were lost
> in the noise. When using a narrow filter they can be seen
> quite clearly.
>
> However - and this is the interesting bit - the level of the
> harmonics relative to the fundamental can be varied by
> changing the LIN OUT level. On my K3 reducing LIN OUT to 003
> and they just about disappear. (Obviously that also depends
> on the strength of the input signal.)
>
> It seems to me that there is some non-linearity in the audio
> stages that sets in at a fairly low level. I'm not an expert
> either, but might the isolating transformers in the line
> output be the cause of this?
>
> -----
> 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>
> --
> View this message in context:
>
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