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

Poul-Henning Kamp phk at phk.freebsd.dk
Sat Jul 5 02:43:26 EDT 2008

In message <486EC7F0.10006 at xtra.co.nz>, Bruce Griffiths writes:
>Poul-Henning Kamp wrote:

>> Look at:
>> 	http://phk.freebsd.dk/misc/L6/
>Nonsense, although it may work in favourable cases where the signal 
>levels arent too disparate, in the more general case this isnt true.

Bruce, you are input-resistant, please read what I write:

1. I am not trying to solve the general case.

2. I am quite happy for it to work only in "favourable cases", because
   most people in the western hemisphere live close enough to a Loran-C
   for it to be a "favourable case".

>Thats obviously fine for some Loran applications but you haven't 
>demonstrated that its also true when attempting to simultaneously track 
>another signal of interest that is relatively weak.

Yes I have, but you seem to refuse to read it:


>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.

This is *not* an attempt to build a shiny complex, gold-plated contraption
that can drag out a signal from half-way around the world in Hi-Fi
quality, described as:

>In which case a dedicated ST32M103 for Loran and another for 
>MSF/WWVB/JJYDCF77 etc is appropriate together with optimised analog 
>front ends, bandpass filters, notch filters and orientation of the 
>individual antennae to null strong interfering signals should cope with 
>most problematic sites.

That's exactly all the stuff I'm trying to avoid.

What I'll build is an <EUR100 single-chip receiver that will
discipline an OCXO or Rb against the strongest Loran-C signal

... And make an excellent platform for experimenting with SDR
on other VLF time/frequency signals.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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