[time-nuts] WWVB phase plots

[Poul-Henning Kamp]

In message <2D539724-9C95-497F-8539-36A9840AC279 at gmail.com>, Dennis Ferguson wr
ites:

>DCF77's AM modulation is a much better fit for what they did,  [...]

Well, with a footnote about a few details, such as only 1 hour leap-second
warning, but yes, it is a very robust signal.

>It is also the case the DCF77's phase modulation probably isn't as good
>as it could be if the goal is to find it in the noise since it only swings
>+/- 15 degrees rather than +/- 90.

When they started it, a lot of DCF77 frequency receivers existed
and 15 degrees were as much as one particular widespread military
model could stay in specs with.

That is also why the sign of PM signal follows the bit in the
second pulse, so that the average PM code is close to zero
in the long run.

>Its big advantage might be that it
>is high speed, with lots of transitions, so you can probably measure
>phase alignment pretty accurately with that.

As usual it depends on your averaging period and thus stability of
your timebase, but 20 microseconds isn't too hard 1200 km from the
transmitter.

If you want to measure propagation effects really precisely, DCF77
is your signal :-)

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