[time-nuts] WWVB PM Receiver

[Peter Monta]

> Have you actually tried it and gotten it working, except possibly in a
> very strong signal area?

This is precisely the issue.  Squaring the WWVB signal results in a
significant SNR penalty.  At high SNR it doesn't matter that much; at
low SNR you are in a world of hurt.

I had suggested to John Lowe that they consider retaining some carrier
in the signal, which would be trivial to do---instead of a modulation
index of 180 degrees for BPSK, make it 120 degrees or 150 degrees, so
that there remains a little bit of pure carrier at 60 kHz that's
trackable with PLL receivers.  He said something about being receptive
to the idea, but apparently it was not adopted, since the latest
document still says antipodal BPSK.

Ironically, GPS is heading in the opposite direction.  The legacy C/A
and P(Y) signals have no unmodulated pilot spreading codes, while the
newer ones at L2 and L5 have strong pilots that allow much better
tracking.

Cheers,
Peter

ps: what happened to the public comment process?  Did I miss the window?