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

Carl Walker carl at icmp.com
Thu Jul 3 18:38:04 EDT 2008


Therein lies the rub; you'll have a family of signals of widely varying
signal strength over a fairly large bandwidth. A real challenge for the
analog part of the receiver design.

How many bits of A/D do you have at 1MS/S with this device?

I've worked on several successful commercial LORAN-C receiver designs
over the years - all of them with linear front ends and hard limiting
back ends to interface with the tracking logic. These provided very high
performance in terms of zero crossing displacement vs signal strength -
but were designed to avoid allowing anything we could possibly exclude
outside of the 20 percent bandwidth needed for LORAN to make it through
the receiver to the limiters - to avoid the "FM capture" effect one
often sees with a limiting receiver. Good quality front end filtering
with low group delay distortion were the order of the day for
performance - along with notch filters for the strong LF RTTY signals
that were always annoyingly close by in frequency.

Receivers without hard limiting and direct analog sampling by A/D were
just becoming practical from a design standpoint when I left the LORAN-C
world for greener pastures.

I'm happy to join in on the design if there's interest.

-Carl



On Thu, 2008-07-03 at 21:38 +0000, Poul-Henning Kamp wrote:
> In message <20080703.230345.407454645627532368.cfmd at bredband.net>, Magnus Danie
> lson writes:
> 
> >It would be nice to have LORAN-C, MSF and DCF-77 in the same solution if
> >possible. I am sure some of the US signals can be included.
> 
> It's trivial to do phase-tracking on any moderately strong CW signal
> at the same time, so that could easily be done using the same chip.
> 
> The analog side would need to allow for those signals also then.
> 





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