[Elecraft] OT - sound cards

[David Gilbert]

OK, now that sounds a lot like the issues I had when I first began using 
pre-recorded .wav files for contesting.  I got several reports of "hum", 
"noise", or "whine" on my transmitted signal ... all of which went away 
when I disconnected the RS-232 cable from between the computer and the 
K3.  As I have mentioned several times here before, it took a very short 
piece of shielded braid between the chassis of the K3 and the chassis of 
the computer to fix it so that I could reconnect the RS-232 cable 
without issues.  I started with a couple of feet of braid and had to go 
all the way down to eight inches before I could no longer notice the 
problem.

You don't say what measures you've taken to bond the chassis of your K3 
to your computer, but that would be my first suggestion.  Your symptoms 
sound almost identical ... even with respect to the noise during pauses 
and the metallic twang at the end of words.

Regarding sound cards for SDR use, certainly the great majority of cards 
out there would have major deficiencies ... most especially for noise, 
but also for dynamic range and sampling rate.  And as you say, many 
don't even have stereo inputs.  N8LP keeps a list of recommended cards 
on his web site with good information on the pros and cons of each.

73,
Dave   AB7E


On 1/9/2012 8:50 AM, Erik Basilier wrote:
> Dave, "decent quality" may be a somewhat subjective concept. Without the
> software noise reduction in the computer, the microphone recordings sound
> very good, except for that noise which is noticeable in pauses. With noise
> reduction on, the situation is reversed: Low noise during pauses, almost
> like a noise gate, but artifacts during words. To be more precise about the
> artifacts, I don't notice a great deal of reduction in higher audio
> frequencies as has sometimes been observed in radios' noise reduction
> algorithms, but mostly a metallic twang, similar to "robot speech" in an old
> sci-fi movie, which is most obvious at start of recording and at the end of
> words, where the speech signal level is close to zero. (This is all using
> the standard Sound Recorder that comes with Windows 7.)
>
>
>
> The KX3 I/Q outputs may for all I know have sufficient levels that they can
> feed the sound card's line input. That input doesn't necessarily have the
> same noise problem as does the microphone input; I have never tried the line
> input on this rather new PC. To clarify, when I referred to past digital
> mode usage, it was not on this computer but on either an older desktop or on
> the old laptop. As I recall from the small number of qso's using the laptop,
> the results may have been inferior on receive compared to the old desktop,
> which had a mid-level brand name PCI soundcard.
>
>
>
> I don't think it fair to expect Elecraft to somehow guarantee that a user
> who wants to make use of the KX3 I/Q outputs will get optimal results with
> all computers' sound cards. For starters, most laptops obviously won't do
> the job without an external soundcard, since they don't have stereo inputs.
> I would expect that a good internal sound card will do a better job than
> most motherboard-integrated "sound cards", and that a good external one will
> perform best, even if one doesn't need a high sampling frequency for a given
> application.
>
>
>
> I would not assume that the noise performance of the microphone input is
> determined by the quality of the sound chip, but that the layout of the
> card, as well as decoupling and isolation components play a significant role
> in preventing sub-millivolt noise signals from entering the signal chain at
> some point before digitization.
>
>
>
>
>
> 73,
>
> Erik K7TV
>
>
>
>> If you can't even make decent quality voice recordings, you have something
> else wrong.  Unless it is simply defective, even the cheapest sound chip out
> there isn't going to act like you describe.
>
>
>
> And what exactly do you think the I/Q outputs of the KX3 are going to be
> using?
>
>
>
> Dave   AB7E
>
>
>
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