[time-nuts] WWVB BPSK Receiver Project?

[J. Forster]

Why make it simple when complicated also works?

-John

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> On 3/15/12 7:49 AM, J. Forster wrote:
>> Suppose the modulation is not present. The output of the phase detector
>> that steers the local standard ot indicator works correctly.
>>
>> Now reverse the 60 kHz carrier. The phase detector works exactly thye
>> opposite way...  wrong.
>>
>> Now alternate between 0 and 190 degrees.
>>
>> The loop alternate works between exactly right and exactly wrong...  it
>> dithers around and the output is a measure of the ratio of 1's to 0's
>> and
>> is utterly useless.
>>
>
> and the cleverness of the  Costas loop is that it uses (an estimate of)
> the current data bit (the output of the I arm) to flip the sign of the
> error signal from the quadrature arm.
>
> There's a lot of scope for modification of the basic linear Costas loop.
>   Hard/soft limiters in either or both arms, you've got three filters
> (the two arm filters and the loop filter) to fool with, plus all sorts
> of schemes using "data aiding" where you get feedback from your symbol
> slicer to help do a better job on the carrier tracking.
>
> You can also run your loop with hard limited signal input (makes the
> "mixers" turn into XOR gates).
>
> If you don't need the bits in real time (i.e. you can tolerate some
> latency), then you can also build tracking loops that effectively "look
> into the future"; i.e. make decisions on carrier and bit at time t using
> future data from t>now, as well as t=[-infinity, now].
>
>
> Enormous literature out there on this, and it's been grist for many a
> Master's or PhD dissertation.
> All in a quest to get ever closer to the Shannon limit...
>
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