[time-nuts] Near-perfect chip for Loran-C frequency

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Jul 3 21:24:37 EDT 2008


JJY(40kHz, 60kHz) HBG(75kHz) DCF77(77.5kHz), MSF(60kHz), WWVB(60kHz) all 
use AM to encode the time using different pulse widths to denote markers 
, 0 and 1 respectively.
WWVB, JJY reduce the power by 10dB to encode 1, 0 etc so that a residual 
carrier is always present.
WWVB also phase modulates the carrier at 1/3600Hz (period = 1hour) with 
a duty cycle of 5/60.
MSF and HBG  use ON/OFF keying.
DCF77 encodes 1, 0 etc by reducing power to 25%, in addition DCF77 phase 
modulates the carrier with a PRBS.
Since the minimum pulse width used is 0.1sec the receiver's effective 
bandwidth (when receiving WWVB, MSF or DCF77) need not be more than a 
few Hz.

Bruce




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