On 6/15/2020 4:55 PM, Wes wrote:
OK QSL.
All of my computers have soundcards including the, soon to be replaced,
shack Lenovo laptop. I tried a TASCAM US-100, highly recommended by
K9YC, without seeing any improvement over the Lenovo on digital modes.
Hi Wes,
You might want to look at the piece I wrote on the topic, which details
my testing. It was pretty rigorous. The USB interfaces I recommended
were equally good, decoded to much greater signal to noise levels, and
produced almost twice as many decodes as the sound system built into the
two T43 Thinkpads used for the tests.
Pulling out the weakest signals requires a lot of dynamic range if very
strong signals are present, and cheap A/D converters can have poor
linearity close to the low end of the dynamic range. WSJT-X uses 48 kHz
16-bit, theoretical 96 dB, real life more like 90. It's not unusual for
there to be locals 30-50 dB over S9 when the band is open, so every
little bit of dynamic range can matter when you're trying to work the
weak ones. All of this is why I started my search in the semi-pro audio
world.
One thing I differ with in the WSJT-X instructions is to set band noise
to 30 dB on the green voltmeter bar. That's fine for modes like MSK144
and ISCAT B, but gives up FAR too much dynamic range for modes like FT8,
FT4, JT65, and JT9.
73, Jim K9YC
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