Jim, VLF,
Am 12.03.2011 01:51, schrieb James Moritz:
Dear Andy, Wolf, LF Group,
Over last night and today I did some further tests with my cheapo USB
sound card and calibration source, but this time using a different
laptop PC. Result - after some fiddling, sample rate error indicated by
SpecLab matches measured error of clock crystal frequency, and a nice
glitch-free spectral line with 180uHz FFT resolution. So the erratic
measured sample rate would seem to be more specific-PC-related than
sound card related. I also got glitch-free results using the internal
sound card of the desktop machine I tried the USB sound card with
previously, which I guess would at least suggest the cause of the
problem is not within SpecLab.
[...]
Absolutely! I have done some TX tests in the last weeks after the
mishap in my 10th experiment. There the DFCW-600 transmissions were
quite fuzzy. I found that the reason seems not the be a EMC problem
(strong local E fields near the antenna) but rather the PC. Local tests
with locking to DHO38 showed that the signal was still fuzzy, so the
GPS module isn't the source of errors as well.
Later i found that the signal is much clearer with another PC (more
than 10 years old HP notebook, once running at win95).
Back to the netbook (running at win7): In the task manager i observed
the CPU load and found some short and sudden peaks to 100% although no
other programs were running and WLAN was disabled. I knew that
everything was fine in the 9th experiment, with exactly the same
hardware. So something must habe been changed.
The solution: Before some time i changed the netbooks energy saving
mode. It reduces the CPU power if traffic is low. But the reduced
power seems not to be enough for SL, sometimes. So the system toggles
between low and high load and this seemed to produce the massive phase
glitches. Now i choosed "maximum power" mode (QRO! :-) )and get
a nice and stable trace, even in the 6000 window. The trace looks
"perfect" in 600 of course.
So i hope to be able to produce a well readable signal in my 11th
experiment that will be in April.
73, Stefan/DK7FC
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