Soft Rock exciter update
fgentges at mindspring.com
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:
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.
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.
> Tacos mailing list
> Tacos at amrad.org
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