[Elecraft] k3/psk on laptop

[Joe Subich, W4TV]

Jim, 

> I agree, Joe, but do so on the basis of far less information than 
> you and Simon, both of whose work I have a great deal of respect 
> for. Sound cards are wildly variable in their quality and 
> characteristics, and virtually all have pin 1 problems. But if you 
> understand how audio level matching works and do the bonding I 
> recommend to eliminate the hum and buzz voltages that exist 
> between equipment that you're interconnecting, most computer sound 
> cars, laptop or otherwise, will work very well. 

While there are certainly "pin 1" problems contribute to the 
problem, the real issue is the high level of internal circuit 
noise on the motherboards of many laptops and even desktops. 
I have measured noise floors in the area of -60 dBu on many 
occasions with NOTHING connected to the soundcard inputs.  

When that is coupled with transceivers from the "big three" that 
have line level outputs 20 dB below the 1V RMS the computer sound 
cards are expecting, the "system" dynamic range is less than 40 
dB!  Consider that the audio level at the "line" output of many 
transceivers is only -50 dBu with an antenna connected listening 
to a "quiet" band and you can see how difficult the situation 
becomes. 

On the other hand, if one has a "good" sound system - the Audigy 
2ZX in one of my test desktops has a noise floor around -105 dBu 
and the soundcard in my HP laptop is around -85 dBu the situation 
is considerably different.  

Still, external sound and control interfaces (shameless plug - 
like microHAM DigiKeyer or microKEYER II) make a lot of sense 
just for one reason - if they contain a very low noise preamp 
(like the microHAM units) they will the 100mV signal (AGC limit) 
from the average transceiver and bring it UP to 1 V RMS which 
improves system dynamic range by 20 dB and makes operation with 
signals all the way down to the received noise level much more 
reliable.   

> Another BTW -- I am told that most laptop mfrs farm out their 
> sound cards to a third party mfr, and they're a commodity. That 
> adds to the wide variation. 

A lot of the laptop manufacturers farm out the design and 
fabrication of their motherboards to "design/build" shops 
in the far east - a trend also extends to consumer desktop 
systems.   Most of the design/build shops do not pay attention 
to the on board noise levels as long as the external/radiated 
levels are within limits of Part 15 or the EU equivalent. 

BTW, to answer Ed's question ... even a limited dynamic range 
is generally satisfactory for "narrow bandwidth" operation. 
If one is doing RTTY or PKS31 with a narrow (300 - 500 Hz) 
filter, dynamic range is not a concern as even the weakest 
signal, as long as it is above the receiver noise floor, will 
be strong enough for the soundcard/software to demodulate. 

Finally, from an operational point of view you want to separate 
the radio from Windows' "beeps and boops."  If you use software 
that announces DX stations,  run an e-mail program on the ham 
computer or play video games on the same machine as you use for 
RTTY/PSK the chance of other noises getting on the air is much 
reduced by leaving the "other stuff" on the Windows default 
sound card and running the digital mode applications and voice 
keyers (contest loggers) on a dedicated soundcard. 

73, 

   ... Joe, W4TV 
  





> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jim Brown
> Sent: Wednesday, June 11, 2008 11:43 AM
> To: elecraft at mailman.qth.net
> Subject: RE: [Elecraft] k3/psk on laptop
> 
> 
> On Tue, 10 Jun 2008 22:51:02 -0400, Joe Subich, W4TV wrote:
> 
> >I hate to disagree with Simon but I do want to answer the old 
> >wives' tale about internal sound cards and laptops ... 
> 
> I agree, Joe, but do so on the basis of far less information than 
> you and Simon, both of whose work I have a great deal of respect 
> for. Sound cards are wildly variable in their quality and 
> characteristics, and virtually all have pin 1 problems. But if you 
> understand how audio level matching works and do the bonding I 
> recommend to eliminate the hum and buzz voltages that exist 
> between equipment that you're interconnecting, most computer sound 
> cars, laptop or otherwise, will work very well. 
> 
> My piece on interfacing is 
> 
> http://audiosystemsgroup.com/HamInterfacing.pdf  
> 
> It is a Power Point for a tutorial I did for a local ham club. The 
> tutorial also exists as text -- it's in Chapter 7 of the RFI 
> tutorial -- Solving Problems in the Shack. Both of these pdfs are 
> written to help hams UNDERSTAND the issues, and provide simple 
> step by step solutions. 
> 
> http://audiosystemsgroup.com/RFI-Ham.pdf   is the tutorial.
> 
> BTW -- my limited sample of laptops over the past 10 years has 
> been almost entirely with Thinkpads, specifically T20-series and 
> T40-series. I bought them new and paid big bucks, but they are now 
> available as used, off-lease units with a legal version of Windows 
> at very modest cost. The T20 and T30 series have a COM port. Later 
> ones do not. 
> 
> Another BTW -- I am told that most laptop mfrs farm out their 
> sound cards to a third party mfr, and they're a commodity. That 
> adds to the wide variation. 
> 
> 73,
> 
> Jim Brown K9YC
> 
> 
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