[ntp:questions] Re: Clock accuracy & auto setting :digital television does a crap job of providing time services...
mikehack at u.washington.edu
Tue May 2 10:22:04 UTC 2006
Has anyone experimented with QAM or PSK around 60 KHz?
Theoretically one does not need to transmit QAM or PSK all the time,
allowing for CW pll and frequency locking at say every 10 or 20 minutes.
>>>>LF time services are OK, and are necessary over large transnational
>>>>regions -- like Sub Saharan Africa, Australasia and South America ...
>>>>any new LF service needs to be more technologically advanced than WWVB,
>>>>MSF or DCF77 and its Swiss twin. In these regions 10 LF frequencies need
>>>>to be allocated, but the signal to be transmitted needs to be more
>>>>WWVB or DCF77 -- maybe using some form of low complexity PSK or low
>>>>complexity QAM and 240 hz to 480 hz of bandwidth. The signal must be
>>>>futureproofed -- as above.
> One thing to remember is that LF stations were originally designed, and
> still serve, another important purpose: to provide precise *frequency*
> measurement capability. The original intention of WWVB was to provide a
> stable carrier frequency in a spectrum that has minimal ionospheric and
> propagation disturbances. The original WWVB receivers were phase-tracking
> units that allowed a local frequency standard to be directly compared to
> the USFS.
Part of the solution is inevitibly creating new LW time stations.
Only 1/3 of the US (& CA-MX) LW "Time Signal Station" spectrum allocation is
being used -- leaving room for at least 2 transmitters (61 & 59 Khz).
Potentally 62 Khz could be used as well. Canada / Australia / NZ have no LW
time station, a sad loss to their infrastrutre.
> One of the advantages of the current modulation scheme is that it doesn't
> mess with the carrier phase. If more complex modulation schemes reduce or
> destroy the ability to phase track the carrier, one of the primary
> purposes of the LF stations will be lost.
More information about the questions