[time-nuts] Alternative WWVB Spectracom solution

[Tom Van Baak]

Since the topic of WWVB came up again, here's another idea.

A number of people still want to use (hp, or Tracor, or) Spectracom WWVB receivers as frequency standards or to maintain NIST traceability. As has been discussed on the list, these receivers no longer work now that the enhanced WWVB format is in effect 24/7. Paul Swed's Costas loop project is a nice hardware solution.

I'm wondering if anyone wants to help on a mostly software solution. Here's the idea -- if you already know the time of day to a few milliseconds (from NTP, GPS, etc.) it should be simple to generate the live 1 baud data of the new PM code. The only hardware you need is an analog inverter/switch which then applies either a 0 or 180 degree shift to the antenna signal, based on the predicted state of the PM code for that second.

In this case, every second, your local phase shifting neatly cancels the Ft Collins phase shifting. The PM bit prediction and edge timing don't have to be perfect, just close enough that the 60 kHz PLL stays happily locked.

The advantage of this approach is that the existing WWVB phase tracking receiver can remain completely unmodified. You would simply insert the programmable inverter inline between the antenna and the receiver. For testing even a DPDT reed relay might do the job.

It would be a good project for a RPi (running an NTP client) or an Arduino (using a cheap GPS NMEA+1PPS receiver). If you can spot holes in the design let me know. It seems too simple to be true.

/tvb