Okay, I've been thinking (somewhat abstractly, since I have had relatively little free time lately) about what I eventually want my beacon transmitter to be. One of the issues with it is that I'd like it to be relatively autonomous and lower power: I'd like it to be able to run for weeks at a time without human intervention. I'd also like to use it for WSPR beacon transmissions, much as my original experimentation that I carried out. The trick for making a long term WSPR beacon though is time synchronization: WSPR transmissions begin on even numbered minutes, and must be accurate to a couple of seconds or so. The DS1307 I've been playing with only has that accuracy for a day or two: so I need something better. A few ideas leapt to mind:
- Temperature control the whole thing. I suspect this only postpones the problem for a period of a week or so, rather than curing it.
- Synchronize using a GPS. I'd only need to wake up for a few minutes every 12 hours or so to keep it going. Still, seems pretty high tech.
- Add a receiver for 10Mhz time signals. Nice, doable with technology I have on hand, but perhaps needlessly complicated and probably more expensive than...
- Using a WWVB integrated receiver. These are about $10, and have very low power consumption. Less homebrew, but perhaps a reasonable choice.
Digikey has 'em in stock for ~$10, falling to about $8 if you order 10.
Digi-Key - 561-1014-ND (Manufacturer - CMMR-6P-60).
My experimentation with oscilloscope displays made me wonder what the oscilloscope clock by Sparkfun/Dutchtronix used. It turns out to be a $5 dual parallel input DAC from Analog Devices, even available as a 20 pin PDIP. It can apparently do 833K samples per second, making it quite a bit faster than a conventional sound card like I was using. Archived for future playing.
AD7302 Digital to Analog Converter