[time-nuts] WWVB BPSK Receiver Project? (fwd)

[Jim Lux]

On 3/15/12 3:27 PM, Poul-Henning Kamp wrote:
> In message<Pine.LNX.4.64.1203152001370.3542 at tesla>, Marek Peca writes:
>
>
>> Yes, it should work on any USB audio capable OS, ie. Linux, Windows, MacOS etc.
>
> I would like to recommend against this approach for a number of reasons.
>
> First, yes, while you can do undersampling and such, it puts very high
> requirements on your analog filters.
>
> The reason I use 1MSPS is that it allows me to use a very sloppy low-pass
> filter filter which just cuts off somewhere around 150-200 kHz, and do
> everything else in software.

and if you have any sort of processing behind the 1MSPS, you can do a 
simple digital filter and decimate.

>
> This means that I have no phase/group-delay distortion in the analog
> part that I need to compensate in software.
>
> It also means that I don't have to change hardware to play with different
> signals, they're all there, all the time, for instance the stuff under
> 	http://phk.freebsd.dk/Leap/
> is pulled out that way.
>
> If I, based on my design, were to design a gadget for doing VLF
> time-nuts stuff, it would be:
>
> Floating Input trafo with center-tap for powering antenna
> 16 bit 1MSPS ADC
> ARM chip
> 10MHz clock input
> 1PPS sync input
> 1PPS sync output
> (DAC output for {Rb|Ocxo}DO use ?)
> 1-4MB RAM
> USB2 interface
>
> Sending 2MB/s through a serial port profile is not a big problem
> for USB2 or for that matter for an operating system, so you can
> easily grap full spectrum and play with your your PC, and once you
> have made some of it work, you can compile the same code and and
> download it to the ARM chip, and use the serial port only for
> stats/summary/(Tek4010-graphs) or you can use another USB profile
> or whatever.
>
> The ARM chip is plenty powerful to do pretty much anything you
> are to on its own once you give it the code to do so.
>