A No-Sync Solution

[NZ0I]

I always thought it would be great to use a so-called "atomic clock", one that periodically synchronizes itself to WWV, to keep ARDF transmitters precisely timed without any need to manually sync them. So here's a way-out idea:

While it is an expensive solution, it should be possible to add that self-syncing capability to these transmitters using GPS receivers. Consider this project at SparkFun:

https://learn.sparkfun.com/tutorials/alphanumeric-gps-wall-clock

The GPS module that goes into that project (https://www.sparkfun.com/products/13670) costs $40. It only consumes 37 mA in continuous tracking mode, and could be shut down when not needed, to save battery power. Each transmitter would need its own GPS module. But with that capability the transmitters could remain precisely synchronized with no action required on the part of the user. They could also automatically adjust themselves for Daylight Saving Time and leap year. Also, since it is a GPS module, the transmitters could be aware of their locations... though I'm not sure how big an advantage that is. I suppose it would allow an organizer to read the transmitter positions for creating a accurate master map, even if one or more of the transmitters had been misplaced in the field. Broadcasting their positions, say using RTTY, might also prove helpful if one of the transmitters was ever stolen!

Adding a GPS module only to the Control Head would ensure that it always has accurate time, that could then be used to manually sync each transmitter. That would be more affordable.

[Patrick R. Sears]

It would be really nice to have a no-sync solution.

What about combining it with a charging solution?  I like systems where the radio is stored in a docking station and it's guaranteed to be charged when you grab it.  The charger could have the GPS module or some other way to ensure a time standard and with a few extra wires it communicates with the transmitter to ensure it's synced.

Of course it makes designing the charging circuit on the transmitter much more of a pain.  We can't just have a plug that disconnects the batteries from the main PCB when the charger is plugged in since the PCB needs to be powered to communicate with the charger.  And we lose the transmitter's ability to know where they are in the field.

Just a thought.

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[Gerald Boyd]

I think this is a very good idea.

Doing A quick check on hobbyking there are cheep GPS receivers ( less then $15) for quads.

Only downside that there is no data sheet for serial stream formats.

However a serial port capture or more detailed check on the internet may fix that.

Jerry
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[Charles Scharlau]

When running the USA ARDF Championships back in 2006, we were using the same rechargeable batteries for both the 2m and 80m events. And the same transmitters too, since they were dual-band Russian-built transmitters. We had seven transmitters (six and one spare) and seven SLA batteries for them. All the devices were in use for 1) Practice events, 2) Demonstration events, and 3) Competition events for four consecutive days. What we discovered was that we needed all the transmitters to be charging simultaneously whenever they were not in use. Otherwise they would not all be fully charged prior to each event. We had lots of extra power in those batteries, and probably could have run several events without ever charging, but that made the batteries much heavier and more expensive than necessary.

So any charging system should be designed to charge (and sync) multiple devices simultaneously. Having a separate charger for each transmitter would also be more expensive, since each would need its own GPS unit... meaning that cost-wise we would be no better off than if we had a GPS in each transmitter. Charging through a USB port (FTDI) would provide connections for communications between the charger and the transmitters, and would be a nice standard for having communication between a charger and transmitters... at least when using LiPo batteries as does the optional feature now supported in the schematic.

Jerry's post about less expensive GPS units just came in as I was writing this. I wouldn't be too concerned about the lack of documentation. Most manufacturers use one of only a few chipset options. If we can determine which chipset the $12 units utilize, we should be able to get the specifications we need. We would just need to do some research before designing them into the transmitters. Getting some user reviews might also help determine how reliable they are.

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