On 8/4/17 7:22 AM, Tom Van Baak wrote:
We were originally going to put a 5071A-locked beacon on three ham
bands, but decided WWV and CHU would be better sources, and logistics
were turning into a problem: I'm going to be doing my wideband recording
from a cottage in northern Michigan. But I'm still a time-nut, so the
receiver will be GPSDO-controlled, and there will be a stratum 1 NTP
server in the cottage to provide timestamps. :-)
John
Hi John,
My favorite write-up about atomic clocks and eclipses (a null result) is at:
http://www2.mpq.mpg.de/~haensch/oldStuff/eclipse/eclipse.html
There you will find a good summary, thorough methodology, and many plots for
the 1999 eclipse. Plus they posted all the raw data (H-maser, cesium,
rubidium), a time-nuts dream. There is no model for why an eclipse should
affect time at the atomic (quantum) level so a null result is fine. If nothing
else, it sets an upper bound on measurement precision or a lower bound on clock
anomalies, if they exist.
Much more dramatic is what an eclipse might do to the ionosphere, as this may
affect both GPS and HF radio. So I'm very please to see the ham community
milking this rare opportunity for all it's worth.
It is of great interest - the fact that we have an ionosphere (which
helps keep us alive) also is one of the bigger factors in accurate time
distribution from space since the medium is refractive - not only does
it change the speed at which a wave propagates through, but the
propagation path is not a straight line.
The ionization is almost entirely due to the sun. There is some small
effect from terrestrial upper atmosphere phenomena propagating upwards,
and then there's also human caused changes (HAARP and other heaters,
rocket launched clouds of easily ionizable material, and the occasional
high energy nuclear reaction in the upper atmosphere/space).
There's a lot that is unknown about the time constants of the ionization
and deionization, since the usual situation is that you gradually reduce
the solar input (sunset) and increase it some 12 hours later. And
there's not, often, the chance to have a "step function" in the solar
illumination vs horizontal distance.
The real challenge is that it's a short event - with conventional
ionosondes, the sweep is minutes long (which is fine given the usual
slow diurnal variation), which is significantly longer than the duration
of totality. That long slow sweep makes synchronization less critical -
if you start off by a few milliseconds, as long as your receiver
bandwidth is wide enough, you still capture the sweep.
It's not going to happen this time, but something where "all frequencies
get measured every few seconds" would be wonderful. There are some
ionosondes using a broadband PN waveform. And there's some interesting
propagation experiments that have been done over the Cascade mountain
range using TV and Radio stations as a form of pseudo random transmit
signal.
But you could do a real interesting science experiment with several
dozen (or hundred) RTL-SDR receivers, a good oscillator for timing, and
a data logger spread over several thousand km. In conjunction with the
existing ionosondes, you could collect a lot of oblique measurements of
the ionosphere during the eclipse.
Then would come (years of) post processing -
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