[time-nuts] wtd: WWVB info

Bob Camp kb8tq at n1k.org
Thu Aug 6 07:02:24 EDT 2015


> On Aug 5, 2015, at 11:27 PM, Donald <donvukovic at gmail.com> wrote:
> On 8/5/2015 7:55 PM, Bob Camp wrote:
>> Hi
>> Analog Devices has some very nice ADC’s that are directly targeted at
>> doing this general sort of thing. They do not have any “odd” filtering approach
>> that creates issues. Some of the early 192 KHz audio parts did not do very well
>> past 1/4 the clock rate.
> What type of FFT horse power would be needed at 192 Khz ?

A ~$30 FPGA card plus an MCU would be massive overkill. It would also be fairly 
easy to do. A similarly priced ARM board from any of a dozen outfits 
*might* do the trick. I’d do it with:

Analog Devices ADC as a front end clocked at ~ 240 KHz
FPGA board to decimate and filter the ADC samples
ARM board to do the time code -> OCXO stuff and user display.

Could you get away without this or that? Who knows. There isn’t 
enough cost in any of those “chunks” to really matter compared
to the months of effort this would take. 

If I was going to do the front end with what I have sitting here, I’d probably use
the AD7660 clocked at 1.5 MHz (15 / 10 out of the KS box) or one of it’s slower
cousins clocked some other way. 


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