[time-nuts] BPSK Receiver & GPS Antenna siting

[Bob Camp]

Hi

Ok, to *try* to bring this back together. 

There is indeed a valid Time Nuts need for something other than GPS. In reality there are many reasons. One that has not been mentioned is to check on the validity of your long term GPS time estimate Small errors that accumulate can be a really nasty thing …

If you live in the mainland US, there aren't a whole lot of alternatives to WWVB. Propagation is a reality that no amount of wishing will eliminate. HF isn't going to do you much good. Other LF signals just don't get here in any sort of useful condition. 

The only rational way to get time information off of WWVB is to look at carrier phase over many days. We have decades of information about that. Unless they implement a fancy modulation scheme (which they very much have not) we are stuck with phase. 

Making this all happen (or not) with legacy gear is an independent issue of the basics above. I believe that if you can extract phase by some technique, you can re-broadcast a signal that the old gear will work with. Maybe it's easier that that, I hope so, but have not proven that by doing it. 

IF you want to simply do a new phase tracking receiver, there are a lot of bits and pieces you can use. None of them are terribly expensive. The "radio" part of the system (not the antenna, not the frequency standard, not the other boxes that input to the system) likely can be done for < $50 in raw parts. Weather that's a $5,000,0000 receiver or a $200 receiver depends on your markup. 

Back when I bought them new, *none* of the legacy WWVB receivers cost $200. I don't remember any of them being much under $2,000. Would I pay $2,000 for one today? Nope, no more than I'd pay the same for a Loran-C receiver. Just for the record, I wouldn't pay $2,000 for a GPS either. 

Would I dive into a receiver project *before* we see the patent filings? - no. I'm not independently wealthy. Financing the challenge(s) to the likely stupid series of patents isn't something I want to fund. Easy or hard technically has nothing to do with it. It's not worth going broke for ….

Bob



On Sep 27, 2012, at 7:59 PM, Jim Lux <jimlux at earthlink.net> wrote:

> On 9/27/12 4:34 PM, Bob Camp wrote:
>> Hi
>> 
>> A PLL locks to phase. If the phase switches by 180 degrees, the phase tracking switches signs. There's no way to track that. You either need to double the frequency (and thus eliminate the modulation) or demodulate the signal and lock to the result. If you simply put up a real narrow filter and hit it with continuous 180 degree phase shifts, the output will be nothing at all…
>> 
>> 
> that's the whole thing about the inphase arm on a Costas loop.. that gets multiplied by the phase error signal from the quadrature arm and fixes the sign flip from the modulation.
> 
> 
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