Poul-Henning Kamp wrote: > In message <[EMAIL PROTECTED]>, Bruce Griffiths writes: > >> Poul-Henning Kamp wrote: >> > > >>> http://phk.freebsd.dk/loran-c/CW/ >>> >>> >> That is restricted to the Loran-C case only. >> > > You have not actually looked at that page have you ? > Not for a few years anyway. > Hint: "CW" is, as usually, used as an abbreviation for "Continous Wave". > > > Plots without scales are not particularly useful. Given the relatively large field strength (>100uV/m ??) for DCF77 in Denmark perhaps a receiver with an optimised (for DCF77 or other LF station) front end can do better.
>>>> Thats only a 33 dB difference in signal level what happens when the >>>> signal strengths differ by 60, 80 dB? >>>> >>> Then we don't care to track them, because we will not be able to >>> derive a sensible frequency signal from them. >>> >>> >> So how come NIST at WWVH in Hawaii still manges to do this then? >> > > I am happy tell you that NIST has taken great care to NOT inform > me, that they want to replace their very expensive high-end gear > with my <EUR100 gadget. > > Their commercial?? VLF receiver uses a chart recorder and may need replacement eventually. > Likewise, I can inform you that I have neither the budget or level > of ambition of NIST in this area, wherefore a <EUR100 receiver that > will track a couple of loud loran-C signals is plenty to make me > happy. > > As there is the option of adding a high performance front end and disabling the Loran-C code (where its not sensible/practical to use it), then there will be much wider interest in this. >> In the case of LF transmissions you would have us believe that anyone >> beyond 500km (theoretical limit within which the DCF77 ground wave >> dominates according to the PTB- excludes Denmark) from the DCF77 >> transmitter hasnt any hope of usefully accurate (1E-9 or better) >> frequency comparisons against the received signal. >> > > I can get 1e-12 from DCF77, as long as I integrate for about a day. > > Which perhaps indicates that the effect of the skywave interacting with the groundwave isn't too critical as long as you integrate for long enough. > I can get 1e-14 from DCF77, as long as I integrate for about a year. > > Given the frequency of European power blackouts and transmitter maintenance the latter integration period is perhaps a little impractical. > Please don't argue any more until you understand that. > > >> If the system is split appropriately into 2 modules the analog front end >> and the DSP backend, customisation to suit a particular site is easy to do, >> > > If you had read what I wrote originally, you would have realized instantly > that it is perfectly possible to use as complex an analog frontend as > you want. > > The goal of my project is to use as simple a frontend as possible, > and there is nothing you can say to persuade me to make it more > complex than it needs to be. > > Poul-Henning > > > Your original loop antenna should have a lower phase tempco (particularly if a lower TCE coil former than a plastic lid is used) than any ferrite antenna, particularly so if the antenna is resonated. Quartzlock have abandoned the use of ferrite antennas and substituted a balanced shielded loop antenna for this reason for their VLF phase tracking receivers. Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
