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I have stumbled upon this very cheap so called "crystal-less" RF transmitter: http://www.mouser.com/ds/2/368/Si4012-35123.pdf

It says there on page 5 the Carrier Frequency Accuracy is 250 ppm while crystal-less. Does this mean that for a 433 MHz carrier there will be 250 x 433 =

108.25 kHz

maximum drift above or below the nominal carrier frequency ? Does this look like enough for the FSK receiver not to be able to tell the signal any longer ? A few tips on how to program the receiver and whether or not I can get away with a non-crystal-less SiLabs paired receiver would help.

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Your calculations are correct, according to the data sheet and using their ppm figures the actual frequency of 433 MHz could be out by up to 108.25 kHz.

Does this look like enough for the FSK receiver not to be able to tell the signal any longer ?

No, I think a reasonably well designed FSK receiver should be able to lock on to anything in the realm of 433 MHz +/- 1 MHz. The FM demodulator should be designed to exceed the full range of the oscillator offset plus the FM deviation. I don't see this as difficult. Then you have a data slicer after the demodulator and you should be fine.

Remember that the drift is slow moving and a data slicer's speed at traversing across the full receiver demodulated output range will be many, many times faster.

A few tips on how to program the receiver

I have no idea what you mean.

whether or not I can get away with a non-crystal-less SiLabs paired receiver would help

"non-crystal-less" - what are you actually asking here?

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  • \$\begingroup\$ I am talking about regular receivers that do not have the SiLabs patented "crystal-less" technology. Those regular receivers will usually have quite high drifts, in the realm of 10 000 ppm if I am not mistaken (can be brought to 10 ppm with external crystal though). Programming them as in setting their params via SPI / I2C / whatever interface they are using. I am not looking to actually design the receiver :) \$\endgroup\$ – kellogs Feb 15 '17 at 16:09
  • \$\begingroup\$ I read your comment but I'm not sure what relevance this have. Is there something about the answer that confuses you or, do you need additional info in my answer? \$\endgroup\$ – Andy aka Feb 16 '17 at 19:36

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