[time-nuts] WWVB BPSK Receiver Project?

Chris Albertson albertson.chris at gmail.com
Fri Mar 16 00:17:59 UTC 2012


That would be big expensive filter.   All you really need is the
average of the last N samples.
But with WWVB the bits are amplitude modulated at one bit per second.
so you want a big time constant on any AGC, maybe 100 seconds.   If
you are sampling at 192K that would use way to much memory if you
stored each sample.  Better to only keep running statistics.    For
AGC you don't need to process every sample, you can feed the AGC a
subset of the sample stream.     But with a 24b-t ADC you may not need
AGC

On Thu, Mar 15, 2012 at 4:01 PM, Azelio Boriani
<azelio.boriani at screen.it> wrote:
> PHK,
> I'm interested in your circular averaging buffer: suppose 1K long, the 1st
> sample goes into position 0, the 2nd into 1 ... the 1000th into 999 or, the
> 1st gets scaled and then summed with that already present in position 0
> then the result back in position 0? And so on, of course, for position 1, 2
> ...
>
> On Thu, Mar 15, 2012 at 11:48 PM, Chris Albertson <albertson.chris at gmail.com
>> wrote:
>
>> On Thu, Mar 15, 2012 at 3:13 PM, Poul-Henning Kamp <phk at phk.freebsd.dk>
>> wrote:
>> > In message <20120315152620.8347488e049854218aed4aa6 at kinali.ch>, Attila
>> Kinali w
>> > rites:
>> >
>> >>> Do you need 16 bits or can you get by with a 12 bit ADC?
>> >
>> > In general: The more the merrier, for a digital dude like me, having
>> > more bits is easier than getting AGC working correctly :-)
>> >
>> >>> Have you considered using an FPGA for signal processing? It seems
>> >> you need a fairly serious CPU to handle that much data.
>>
>>
>> "That much data" we are talking about 192K samples per second.   I can
>> routinely record multiple tracks of 192K audio and do processing in
>> real time and the CPU meter hardly moves  the bottom.    Even a
>> gigabit per second Ethernet port is not "a lot of data" on a modern
>> computer.
>>
>> FPGAs and DSP come into play if you are talking about tens of millions
>> of samples per second with data rates above say 200Mb/Sec  But the
>> rate from an audio interface running 192K and 24-bits is still under
>> one megabyte per second.    An interesting ratio is the number of CPU
>> cycles available to process one sample.  On my Apple iMac that would
>> be about roughly  200,000 operations per data sample.
>>
>> In real life SDR receivers even an older CPU can process the I and Q
>> channels and maintain a large graphic screen and send and receive data
>> over a network and still not be "maxed out"
>>
>>
>> Chris Albertson
>> Redondo Beach, California
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.



-- 

Chris Albertson
Redondo Beach, California



More information about the time-nuts mailing list