[Elecraft] Re: K3 Audio

Thu Aug 7 05:09:30 EDT 2008

Hi Brett,

yes, I can play with it today evening I hope.
Now having AGC-F, SLP 13 and TRSHLD 6, RF MAX
On TS-850 I have AGC Fast, RF max
All testing on relatively strong signals(more then S7).

But I am not sure possible if "clipping" is before final AF output as 
there are differencies between LINE OUT and PHONES output. But who 
knows...

Generally having some "leakage" -50dB and 3f out of desired signal is 
not seriuos problem for CW/SSB (imho), maybe only for us we use af out 
for some post-processing (Spectran, Winrad,...) or digital decoder 
(PSK, WSJT, WSPR, CW Skimmer,...) can such "ghosts" make some confusions.
Not sure if there can be problem with weak digital signals like WSJT 
(but decoding K2UYH on 23cm some week ago without any problems and 
shortly tested WSPR on 30m band and no problems od decoder recognized 
also).
Maybe all this is more academic but still interesting :-)
Maybe somebody else can report more serious problems with this 
phenomena, I am not using digital modes intensively.

As I am leaving for holiday I am afraid I will not be able to make 
more tests/screenshots during next days - maybe somebody else can 
spend next weekend with some testing :-)
(But taking my K3 and some "HF wires" with - surely :-))

73!
Lexa, ok1dst
K3/10 #727

Brett Howard napsal(a):
> Could you try this test again and just turn down your RF gain a bit?
> 
> Or try turning down your AGC threshold.  I found that if your an
> automatic kinda guy that a threshold of 2 with a slope of 10 works
> pretty good.
> 
> I found that when listening to a CW station if the AGC was threshold was
> set to high and the RF gain was maxed out that I did get a lot of
> harmonic distortion.  I found that turning down the RF gain helped a
> little bit but once you hit a certain point poof most of it goes away.
> It seems like there is a stage being driven into clipping even before
> the audio and thats where the harmonics are coming from. 
> 
> Even from the two previous recordings that I did where I preferred the
> K1 because the narrower filter settings sounded very harsh on the ears
> well it just so turns out that some better AGC settings (or simply
> turning the RF gain down) results in a MUCH more pleasant sounding rig.
> Another one of those places where the ultimate adjustibility of the K3
> caused me some grief but I learned something about the rig and had fun
> with the hobby so still yet color me happy! 
> 
> Hope the rest of you are having as much fun finding and figuring out
> things as I... :)  
> 
> New K3 tagline.....
> 
> Elecraft K3....  Its not an appliance!
> 
> ~Brett (KC7OTG)
> 
> 
> On Wed, 2008-08-06 at 23:53 +0200, Alexandr Kobranov wrote:
>> I just made two basic samples using K3 and TS-850 using Firebox 
>> external soundcard and Winrad SW.
>>
>> You can see screenshot from K3 line-out audio on
>>
>> http://www.ok1kei.org/K3_audio/line_out_firebox_winrad.jpg
>>
>> This is K3 with 400Hz roofing filter on some stable carrier.
>> LINE OUT setting on level 9.
>>
>> Then the same signal with the same af level (no change in Firebox 
>> input mixer settings) with TS-850
>>
>> http://www.ok1kei.org/K3_audio/ts850_af_firebox_winrad.jpg
>>
>> This is my TS-850 with 400Hz inrad filter and output from phones jack.
>> There are also some "ghosts" in af spectrum, generaly more noisy, but 
>> no "image" of passband af signal visible.
>>
>> As I do not believe in overloding of the Firebox soundcard (the same 
>> conditions for both RIGs so if overloded so in both cases...), there 
>> is something to explain.
>>
>> Comments?
>>
>> Thanks for your attention,
>> 73!
>> Lexa, OK1DST
>> K3/10 #727
>>
>>
>>
>>
>> Alexandr Kobranov napsal(a):
>>> I can confirm cca 20dB lower level of 3rd harmonics on front panel 
>>> phones output against rear panel line out. Main versus 3rd harmonics is 
>>> 50dB resp. 7OdB on line-out resp. phones output here.
>>> Just tried with on-board sound card od my Dell workstation.
>>> (using Spectran SW and output level adjusted for the same peak out level 
>>> on Spectran screen).
>>> Maybe later will try with Firebox sound card which has better parameters.
>>> Lexa, ok1dst
>>>
>>> Joe Subich, W4TV napsal(a):
>>>>> There is still a bit of a problem on receive audio.  This has been 
>>>>> there for some time and exists in the form of harmonics.  The 3rd 
>>>>> harmonic is quite easy to see and repeatable.  I used HRD to show 
>>>>> this on the waterfall after a conversation with a friend. You can 
>>>>> clearly see the harmonic at..
>>>> You are overdriving your sound card or the line out transformer in the 
>>>> K3. 
>>>> I have measured the third harmonic using an audio spectrum analyzer
>>>> at both the line out and headphone jacks of my K3.  Until the level 
>>>> becomes excessive (> .7V RMS on the Line Out) the third harmonic is 
>>>> more than 50 dB down (Line Out) and more than 70 dB down (headphones). 
>>>> 73,
>>>>    ... Joe, W4TV  
>>>>
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> 