Hi Bob.
> After acquisition, it seems to do some kind of matched filtering for
> "what it expects" to stay synchronized and gets better Eb/N0 performance
> as a result.
You are correct. NIST encourages radio controlled clock manufacturers to
employ bit and frame averaging techniques to improve decoding accuracy. The
frame averaging and the "sanity checks" that take place in firmware take
several minutes _under good reception conditions_ to complete.
WWVB reception quality normally improves at night due to better D layer signal
propagation (and naturally lower noise levels).
While every amateur text I've come across states that the D and E layers
disappear at night, they, in fact, do not. They rise to higher altitudes and
remain ionized through background cosmic radiation. It is this lightly ionized
D-layer that makes LF reception possible beyond the normal range of surface
wave propagation at night.
Oddly enough, I have my K2/100 building experience to thank for discovering
this.
73, de John, KD2BD
Visit John on the Web at:
http://kd2bd.ham.org/
.
.
.
.
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