I should have stated for KG6MZS that my computers do have audio inputs to the
internal cards.
And when I spoke of digital modes, I meant RTTY, the only one I seriously use.
Wes N7WS
On 6/15/2020 8:51 PM, Jim Brown wrote:
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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