[time-nuts] Phase modulation detection/NIST plan

[J. Forster]

Hi Peter,

That's be the hard way, but yes, if the message BPSK coded is computable
and of a known format. If the message contained more than time, like solar
flux, it gets more complicated very rapidly.

A similar thing was done with the Equatorial system 30+ years ago. In that
case, each data bit was broken into something like 32 or 64 chips (I don't
remember). There were two maximally distant, orthogonal chip patterns,
representing 1 and 0. The incoming BPSK message went through a 0 or 180
degree switch, then the IF stages. The switch was driven from a local
(known pattern) chip generator, so that if everything was synced up the
narrow band IF would put out the 0 or 1 that had been encoded. BTW, this
trick vastly improved the system S/N becaust it narrowed the receiver IF
bandwidth many times.

If the chip pattern is not known (fixed) or computable (like a correct
TOD) things go to pot quickly.

Rather than building such a kludge, it would be easier to use the locked
clock in a newly designed receiver and phase compare that to your local
standard directly.

-John

==================






> Any possibility of using the decoded signal to un-do the modulation and
> feed the reconstituted signal to the older receiver?
>
>
>
> On 7/8/2012 12:56 PM, paul wrote:
>> Ei
>> Sorry if I have your name reversed. By taking this approach it
>> eliminates the ability to use wwvb as a frequency reference because it
>> destroys that traceability.
>> Thats what we are trying to preserve. Or at least re-establish for the
>> older phase measuring receivers.
>> Regards
>> Paul
>>
>> On 7/8/2012 12:10 PM, Tofurk Ei wrote:
>>> If the changeover you are talking about is this one:
>>> http://www.nist.gov/pml/newsletter/radio.cfm as a proof of concept a
>>> DVB-T
>>> dongle/upconverter combo could almost certainly handle PM easily to
>>> output
>>> whatever it encodes, when paired with gnuradio..
>>>
>>>   The RTL2832U chip might also be able to handle some low band signals
>>> directly, using direct sampling. No upconverter.
>>>
>>> Regardless, then the data would be fed into gnuradio - the gnuradio
>>> developers GUI is called "gnuradio companion" It has a nifty way of
>>> doing
>>> this kind of thing, one builds a "flow graph" where the actual
>>> demodulation
>>> is simply laid out graphically and tested.
>>>
>>> When everything works to one's satisfaction the file is saved and it
>>> gets
>>> compiled - then it can run - its basically a python script.
>>>
>>> If the modulation scheme is public, I think you can be almost certain
>>> that
>>> gnuradio might be quite useful to rapidly design a tool to demodulate
>>> it.
>>> Perhaps very quickly.
>>>
>>> For the money, one really couldn't hope to beat the flexibility of this
>>> combination in any other manner. If I were interested in trying this I
>>> would join the gnuradio mailing list and ask there. Perhaps the
>>> answer is
>>> surprisingly simple.
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>>
>>
>>
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