[time-nuts] wtd: WWVB info

Iain Young iain at g7iii.net
Sat Aug 8 03:29:18 EDT 2015


On 07/08/15 07:18, Charles Steinmetz wrote:
> Bob wrote:
>
>> Well, at least *some* of the chips out there do not make it to 96 KHz
>> when sampling at 192 KHz. It’s
>> been a few years since I dug into them. Back then a chip that had an
>> internal filter that went to 96K
>> was very much the exception rather than the rule. If the only point of
>> 192K is getting to a 96K bandwidth,
>> a lot of the chip guys missed out on it ….
>
> 192k *audio* ADCs often have input anti-aliasing filters that are only
> 20-50kHz wide.  In that case, the point of sampling at 192ks/S is so the
> anti-aliasing filter does not need to have a brick wall response (as it
> would need to have if you sampled at 48 or even 96ks/S), so it can have
> a flatter group delay over the range of human hearing.

I guess I got lucky. The machine I brought specifically for SDR work
ended up with an (on board) 192kHz sample card, that appears not to have
such filters in.

http://hal.g7iii.net/vlf/vlf1.png and http://hal.g7iii.net/vlf/vlf2.png

You should be able to spot MSF and DCF booming in amongst the low data
LF stations (and odd sprog). This is off my LF antenna, but a long wire
may be sufficient

(In fact a 2M long feed wire to the mic socket was picking up both time
signals by itself for me, but that's another story!)

While not decoding the phase, my gnuradio MSF and DCF receivers are
here: http://hal.g7iii.net/GRC/Radio_Clocks/

I do have a gnuradio TDF decoder as well if anyone is interested. TDF
twiddles the phase on a AM carrier to transmit the time. Originally I
simply used an LPF, but then switched to using the Quadrature Demod
block which was available in gnuradio


Iain


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