FCC Part 15/ISM DIY radios for full duplex microcontroller coms?

[Mr RB]

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Unadulterated, those modules are really just wireless wires. You put 5V to a pin on the TX side, and a 5v signal shows up somewhere on the RX side. That's great and all, because that makes them really cheap. However they obviously have limits, you can't change frequencies, you can't use more than one pair in the same space/time, you can't do full duplex, you can't spread spectrum, you can't change the modulation scheme; you can't do lot's of things. If you want to do this stuff, you can go full out and start reversing and rebuilding the entire thing. But then, you essentially wind up back to where we are now.
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Agreed, you've made some good points there. But now by adding those features you've gone into more complexity, more parts, more effort to build and test etc.

If you're happy to do that for the increased functionality that's fine, but it further narrows your target market of people who would find it useful and maybe build one themselves from your design.

And if you wanted all the channel hopping auto packet type comms there are other pre-built modules that will do that;

NRF24L01 transceiver modules, $6 per pair, 10 for $17 ($1.70 each!)
CC1101 transceiver modules $9 per pair etc

I'm not trying to put a downer on your project, like I said it sounds like fun and I'm sure you can get a lot of personal satisfaction and learning experience. If that's the way you want to go it will be a nice project.