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

Poul-Henning Kamp phk at phk.freebsd.dk
Fri Jul 4 19:54:03 EDT 2008


In message <14647AC2-BDFB-422A-9FCE-BE9D936DF3D9 at cox.net>, "Thomas A. Frank" wr
ites:

>In as much as we know exactly the frequencies of interest, perhaps  
>the analog front end could consist of multiple signal paths with very  
>narrow band filters to separate out the signals of interest (a 60 kHz  
>channel, a 100 kHz channel, plus whatever other channels are  
>desired), then each channel gets an individual AGC amp, and the  
>matched signals are summed back together for A-D?

If you really want to do something like that, notch filters are
a much better way to go.

But as I keep trying to tell you guys: you don't need all that.

Look at:
	http://phk.freebsd.dk/misc/L6/

There are four GRI's: 7499, 6731, 9007 and 8000, each in their own row.

The leftmost plot shows the entire FRI (2 times GRI) and is used
to locate the individual signals (look for one green (master) and
multiple blue (slave) peaks.

The small plots show three stations in each chain, to the extent that
I have been able to locate them by eyeball.  The X, Y designations may
not match the official LORAN-C station names.

The title on each of these plots show the relative signal strength,
and as you can see the 7499M is 44 times stronger than the 9007Y.

The data you see there is roughly 8 minutes worth of data at 
10 bits per sample, 1Msps, processed as fixedpoint in the
time-critical path.

The antenna is this one: http://phk.freebsd.dk/loran-c/Antenna/
and it just has a simple Low-pass filter around 200 kHz.

Unfortunately, the ST32M103 will have neither the RAM nor
CPU power to track that many signals, but how many it can
do remains to be seen.

-- 
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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