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

[Thomas A. Frank]

On Jul 3, 2008, at 7:16 PM, Carl Walker wrote:

> On Fri, 2008-07-04 at 01:02 +0200, Magnus Danielson wrote:
>>> The analog side would need to allow for those signals also then.
>>
>> Naturally. The antenna-amplifier design will need to be more wideband
>> oriented. Should not be too hard thought.
>>
>> Cheers,
>> Magnus
>
> I respectfully disagree; while making the wide-band receiver is an  
> easy
> task, you now have a family of unrelated signals - often of widely
> varying signal strength. Once any of those signals becomes large  
> enough
> to drive the receiver non-linear, you rapidly run into issues.
>
> AGC to maintain linearity isn't practical in this case - since  
> reducing
> overall receiver gain to compensate for one large signal - like  
> WWVB if
> you're close by that one transmitter - will potentially drive down the
> gain for desired LORAN and other signals to the point where you can't
> acquire and track many of the weaker but never the less desired  
> signals.
>
> There's more than meets the eye initially when you attempt a receiver
> design of this type - at least as far as the analog section goes. Once
> it becomes 1's and 0's it's all straight forward - at least as far as
> this old ex-analog guy is concerned ;-)


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?

It might in fact be cheaper to have multiple A-D modules behind such  
filters...

Tom Frank