Soft Rock exciter update

Frank Gentges fgentges at
Sun Oct 1 20:29:37 CDT 2006


I had a really great chat with George Le master this morning at the CARA 
Hamfest this morning.  We gravitated quickly to the sound card problem.  
I have been looking to buy a better sound card for my SoftRock receiver.

Sound cards are typically characterized in terms of audible sound and 
not what we need to interface with an SDR.  Our conversation concluded 
that we at AMRAD may be in a good position to re characterize sound 
cards for this new and unique application.  In addition he brought me up 
to date on the skills of AMRAD member Steve Dove, W3EEE and his 
knowledge and skills in audio engineering.  With a little effort, we may 
have really great expertise on the problem within the group and can zero 
in on what sound cards are able to do. They should be:

1.  cheap

2.  best choice in performance for SDR duty.

One key issue is that the sound cards are rated for "A" weighting 
wherein the card is measured from 20 Hz to 20 kHz with a variant of the  
Fletcher Munson hearing curve and with anything above 20 kHz being 
filtered out for measurement.  When used for a 96 kHz sampling rate this 
is not a good overall measure for the SDR application.  What we need is 
a broad sampling of the many sound cards to see if any do well and if 
not, how to modify one or to design a new one that does.

While many sound cards now perform a 24 bit digitization, overall 
dynamic range is more like 17 bits with the rest of the bits being 
buried in card noise.  We may find a 16 bit card turns out to be the 
best for SDR.  Apparently, many sound cards have excess noise above 20 
kHz which will make them less useful in SDR applications.  This subject 
is potentially deeper than reading a few reviews from the computer 

Thanks to our esteemed Vice President for his insight into the problem.  
Hopefully, AMRAD members can rise to the challenge.

I will be announcing the availability of some dumpster grade computers 
in the next message.  Combined with a SoftRock receiver and good sound 
card the amateur can have a great SDR on the cheap.  I would like to 
call it the  "AMRAD Cheap Thrill for All-You-All".  As many of you are 
aware, I don't do nested acronyms so we will just forget about using 

Then we need to catch up with you on the exciter side of the 
technology.  Similar issues will likely arise on the D/A side of the 
sound card and the software-human interface.

I am copying this to the Tacos list in hope of stimulating some 
discussion and hopefully work and effort on the problem of sound cards.  
Steve, W3EEE may be able to bring light and knowledge onto the problem.

Frank K0BRA

Terry Fox wrote:
> Hey there all-you-all.  The latest here is the soft rock exciter protoype I
> have is working fine on the bench.  I am measuring about 1/2W out on
> 7.060MHz and thereabouts.  Putting the signal through a 40db pad and into my
> homebrew spectrum analyzer, I am measuring the second harmonic down 46db
> from the main signal.
> Now,  I am having to learn the PowerSDR software, so I can make my first CW
> contact with the SoftRock transceiver.
> Terry
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