So here I am, trying to bring up the receive side of this low-power RF link....
I know the transmitter is at least somewhat working, because if I force it into continuous transmit mode I see a correct result on the spectrum analyzer.
And now there's the receiver. Well, a transceiver chip being used as a receiver.
Rather than muck about with trying to do initial bring-up on an AVR - and an ATtiny26 at that, utterly lacking any sort of console - I wired it up to an LPC2148 eval board, and hacked up a little program to run under AGROS and do stuff like initializing registers and polling for status. Having printf available is kinda handy!
After some fiddling, I got it to come up on the right frequency, as determined by putting it in transmit mode. Unfortunately, it appears to be severely modulated, sometimes... and sometimes it comes up clean. Eh? I suspect the VCO is wonky, but the VCO is entirely internal to the transceiver chip.
And then there's the receive path. We all know how to bring up a receive path: apply a signal (for example, by turning on the previously brought up transmitter), and follow it through the IF and demodulator. Here, though... the whole path is internal to the chip. Can't put a scope probe on it.
Grumble, grumble... well, I guess the thing to do is get it to put out a clean signal, consistently, in transmit mode. Once it does that, I'll know the VCO is working OK, and bringing up the receiver makes sense. As things stand now, the receiver has hallucinations, and keeps claiming to be receiving (random-looking) data when there's no signal.
There's this to be said for the itty-bitty chip with everything in a tiny closed package, though: assuming I can get it to cooperate, the complete transceiver section, including crystal & filter/matching components, will fit (after footprint corrections) in a fingerprint-sized area. Couldn't do that with the tech I was using a decade back.
Update: turns out it was something I could put a scope probe on. I'd installed a wrong-value cap on the bypass pin of the on-chip voltage regulator, and the regulator was singing to itself. Think that might make the VCO get a bit wonky? (This wasn't the problem with the other copy of the hardware, which has the correct cap, didn't have a significant AC component at that node, and was showing similar-looking problems. On the other hand, maybe I didn't have the register values right a couple of days ago, when I was working on that one.)
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