What I haven’t quite figured out is how important is this really is
to weak signal digital decoding.
Low noise in a sound card is important to weak signal decoding in two
ways:
1) you want the inherent noise floor in the sound card to be 10 to 15
dB *LESS* than the minimum - receiver noise + "antenna" - noise. On
VHF with a very quiet receiver the receiver noise can be quite low.
2) high noise level in a sound card directly subtracts from the dynamic
range (ADC clipping - noise floor). With a high noise floor, strong
signals either overflow the ADC or the receiver AGC must reduce gain
with moves the weak signals below the (higher) noise floor.
After testing, I settled on a Sound BlasterX G5 model SB1700 which
> tested at about -120dB noise level.
-128 dB relative to what? A quality 16 bit sound card has a theoretical
dynamic range of 97dB - a quality 16 bit card (low noise) will produce
about 90 dB dynamic range in practice. A 24 bit sound card has 144 dB
theoretical dynamic range but a practical 24 bit sound card will produce
maybe 115 dB dynamic range but to take advantage of that dynamic range
the sound card (any audio preamps and the ADC) need to operate with a
supply voltage greater than the typical 3.3 or 5 V USB supply. A 24 bit
sound card with a 5 V (USB) supply will be lucky to achieve 100 dB
dynamic range.
73,
... Joe, W4TV
On 2021-10-31 10:41 AM, SteveL wrote:
Dave,
This interest caught my eye awhile back:
http://members.chello.at/oe1mww/sound-card-check/
<http://members.chello.at/oe1mww/sound-card-check/>
I’ve tested several of the inexpensive (<$10) nameless USB sound card dongles
using his method and saw a wide variety of noise floors - however significantly
higher than a name brand USB card. After testing, I settled on a Sound BlasterX
G5 model SB1700 which tested at about -120dB noise level. How does this compare?
My nameless sound dongles noise level tested -70 to -90dB - a big difference.
What I haven’t quite figured out is how important is this really is to weak
signal digital decoding.
Steve
aa8af
On Oct 30, 2021, at 10:49 PM, David Christ <[email protected]> wrote:
Yes this has been bead to death previously. Jim Brown made a number of
suggestions in a paper from 2014. However the market has changed. Those
models are all discontinued and those manufacturers' follow ons are much more
expensive and have features that are not needed for sound card modes. Any
offerings of these older models seem to be coming from overseas. The $100 and
under market seems to be dominated by mystery brand dongles which are a gamble.
So can any one recommend a tried and true sound card interface for use between
an K3 (without a sound card) and a MacBook Pro (which has no mike or line in
jack)? I would like to hear from people who have actually the unit, not just
speculation.
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