[time-nuts] BPSK decoder for WWVB

briana alsopb at nc.rr.com
Thu Jul 4 08:59:59 EDT 2013


Please read the WWVB article on this. There is a whole section devoted 
on how it can  provide higher immunity to MSF.   I don't think it a 
false advertising claim.

www.jks.com/*wwvb*.pdf

Read the Fundamentals of the new protocol section.

Don't shoot the messenger please.

Brian
On 7/4/2013 2:01 AM, Attila Kinali wrote:
> On Wed, 03 Jul 2013 19:15:40 +0000
> Brian Alsop <alsopb at nc.rr.com> wrote:
>
>> Apparently this modulation scheme is less prone to "jammers".
>> There is is British station which "jams" east coast WWVB.
> The way WWVB implements BPSK does not make it less prone to jammers
> or noise. The idea, to get higher SNR would be to encode a known
> signal onto the carrier which you can correlate against. WWVB does
> not do that. The phase switches every second according to the bit
> to be transmitted. As the bits are unkown (safe the 12 sync bits)
> you have no additional information what the phase/signal is, actually
> you have even less knowledge compared to a fixed phase signal (aka AM only
> modulation), hence lower SNR (= less jamming protection).
>
> Compare this modulation scheme to what DCF77 or GPS does. Both modulate a
> long pseudorandom, but known bit string over the carrier against which you
> can correlate. The effective data bitrate is much lower.
>
> And just for clarity: The jamming resistance of such modulation schemes
> is not inherent in the "known signal", but comes from spreading the signal
> over a larger bandwidth. White noise and random narrow band noise (the
> two most common noise sources over the air) can be "averaged" out by
> the modulation if the bitstring is known. If designed right, you can detect
> a signal that is several dB below the thermal noise limit, like GPS.
>
>
> TL;DR version: The way how BPSK modulation is implemented in WWVB makes
> it more prone to jammers and noise instead of less.
>
>
> 			Attila Kinali



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