[time-nuts] WWVB BPSK Receiver Project?

Wed Mar 14 22:46:48 UTC 2012

Asus has a $30 Xonar PCI soundcard that should do the job.
I have two of the the more expensive  pci-e versions.  Some motherboards
can do a/d at 192 but not as well as the Xonar.

I made a 60 KHz antenna by winding a zillion turns on a ferrite
rod and a padder going into the gate of a FET.   This was in the
1970s.

On 03/14/2012 03:35 PM, Chris Albertson wrote:
> On Wed, Mar 14, 2012 at 3:08 PM, Brooke Clarke<brooke at pacific.net>  wrote:
>> Hi:
>>
>> I sure would like a WWVB BPSK receiver for the new modulation.  The
>> processing gains described in the paper John Seamons linked describes
>> processing gains that are tens of dB above what's possible with the old AM
>> data format.  John has also measures the experimental phase modulation
>> testing, see:  http://www.jks.com/wwvb/wwvb.html
>> The WWB paper "New Improved System for WWVB Broadcast" given at the 43rd
>> PTTI November 2011 is at:  http://jks.com/wwvb.pdf
>>
>> Part of the processing gain comes directly from the BPSK modulation and that
>> amounts to a little over 10 dB improvement, but there's a further 18 dB gain
>> to be had by accumulating an hours worth of data and processing that.
>>
>> I'm sure in time there will be plenty of low cost ICs designed to receive
>> the new signal, but my guess is that many Time Nuts would like to be in on
>> the ground floor.  Also NIST probably would like to get reports on the new
>> signal when they do test transmissions.
>>
>> How to move forward?
> I'd say to go "100% SDR".  In other words a simple front and that
> pushes as much of the functionality into software as possible.   The
> carrier is only 60K.  That is low enough that one can directly
> digitize the RF using an ADC that samples at only 192K/sec.
> 192K/Sec is a common sample rte for high-end audio and you can buy a
> 24-bit dual channel interface for under $200.
>
> So I'd use an antenna (the best would be a shielded loop with many
> turns of wire but ferrite "loop stick" could work) Follow that be an
> RF amp and very narrow filter and then the above 24-bit 192K ADC.
> With a 24-bit ADC you may not need any automatic gain control.   So yo
> are almost sampling the voltage off the antenna, so that's why I
> called it "100% SDR"
>
> Once the data are inside the computer the very next step might be an FFT.
>
> Some good easy to use software is this:
> http://gnuradio.org/redmine/projects/gnuradio/wiki/GNURadioCompanion
> Using this you simply drop function blocks on a screen and connect
> then with lines.  It's a visual drag and drop way to build a signal
> processor
>
> As  an example to build a spectrum analyzer you drop a block the
> represents your audio interface, another for the FFT operator and a
> third for a graph.  Connect them together.    Then plug in a
> microphone and point it as something you want to plot.
>
> If you do use the simplest possible RF front and that can still work,
> followed by a common off the shelf audio interface and then a simple
> graphical programming environment you then will have a wider community
> of people working on this.    You could use more complex technology
> like an FPGA or a DSP chip but then the number of people who would
> know how to help will be a number close to zero.
>
> The RF front end does not need to be sophisticated because much of the
> selectivity and gain control is done in software.  You just need a
> hard low pass filter to remove everything above 60KHz
>
>
>> --
>> Have Fun,
>>
>> Brooke Clarke, N6GCE
>> http://www.PRC68.com
>> http://www.end2partygovernment.com/Brooke4Congress.html
>>
>>
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>
>

-- 
Chuck Forsberg WA7KGX N2469R     caf at omen.com   www.omen.com
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