[ntp:questions] WV/CHU/IRIG audio drivers
David L. Mills
mills at udel.edu
Sun Jan 21 04:46:24 UTC 2007
I've just gone through a round of audio driver upgrades for the WWV and
CHU radio services and the IRIG signal. The documentation has been
rewritten as well. I'm hoping that the CHU upgrade might find users in
Canada to support the continued operation of CHU with three frequencies,
even if the 7335 kHz frequency is moved. As it is, that frequency is
clobbered from sundown to sunup by broadcasters that should be using the
All three drivers have much better accuracy and lower jitter to the
point the radio drivers can track movements of the ionosphere. Expected
accuracy without prior calibration, but with accurate propagation delay
configuration, within 0.5 ms with IRIG, 1 ms with WWV and 2 ms with CHU.
When calibrated relative to a PPS signal from a GPS receiver, the
accuracy is .02 ms for IRIG, 0.5 ms for WWV and 1 ms for CHU. With WWV
the residual errors are dominated by ionospheric movements. These
figures are for FreeBSD 6.1 running on a Pentium 4. Forget Solaris; it
is a terrible platform for squeaky clean time.
In addition to the accuracy improvements, the radio drivers have better
behavior under marginal signal conditions, especially the
maximum-likelihood UART and majority decoder used in the CHU driver. As
we are at the nadir of sunspot cycle, propagation conditions have been
truely awful, but does present the opportunity to improve the algorithms
to separate weak signals from real trash.
To Canada (my father was born there): get the CHU thing running and make
sure the NRC knows it.
More information about the questions