I've messed with a fair number of small beacon circuits and am interested in your comments on this.
I've been using the Epson programmable oscillators for a while, in ISM band HIFER use. They're super cheap ($4 , programmed to your 4 digit places of accuracy).
https://www.digikey.com/product-detail/en/epson/SG-8002DC-MPT/SG-8002DC-PHC-ND/275176 I'll have to re-measure my HIFER into a 50 ohm resistor, but IIRC it's about 4mW output. Programming takes 2 days and it's at your door in a week. What a bargain for FOUR BUCKS.
Following up on Stretch's post of an old familiar CMOS inverter transmitter, I'm going to try replacing what's hanging off pins 11 and 9 in this schematic:
http://new-ham-radio.blogspot.com/2010/07/is-it-possible-to-create-qrp.htmlWith one of the Epson oscillators.
Keying will be handled by an ATTiny 85 stuffed with any of the million keyer software packages available for download. I've not programmed a Tiny but have done so with a Arduino and I think it can use the same IDE. I have one of the dev boards to mess with and a programmer of fine Chinesium quality.
Given that power budgets are where it's at for solar powered beacons, Class E is the way to go. The epson oscillator has a chip enable so keying it from an ATTINY should be straightforward, and the AT TINY can be put into super efficient sleep modes.
Anyone see any major problems with this concept? Digikey has decent shipping ($5) in US and they're fast at programming (2 days).
First application will be a QRSS transmitter for 40M, but if this works, the possibilities are endless, and the frequency flexibility of these things is handy.