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Using SmartRF04, CC1101EB, and SmartRF Studio to determine unknown transmission properties

Brian White1
Prodigy 60 points
Other Parts Discussed in Thread: CC1101, CC1120

Hi all

  I may be on a wild goose chase, but I'm trying to listen in to packets sent by an iClicker remote. It's a little 915mHz remote transceiver used in classrooms for students to send in answers to questions asked in class. The thing is, I only know a little about its transmit configuration and I'm wondering if it's possible to use SmartRF04 or a TrxEB with a CC1101EB to determine the configuration of the packets.

  Here's what I know: the operating frequency is 917mHz and it uses a XE1203F transceiver chip. This chip can only do 2-FSK. Some internet sources of questionable reliability suggest more parameters, but I set the CC1101 to these and it did not work. If I was using my ham radio rig and the clicker was another ham, I'd tune to 917mHz and listen, then once I hear a chirp, I'd play with the receiver and demod until it was intelligible. Is there a way to set the 1101 "wide open" so I can do something like this? Ideally, I could start from a situation where I see the signal at 917mHz, then play with one setting (frequency shift?) until I get that right (how could I tell?), then set the next one, etc.

  For this to work, there needs to be a reasonable sequence of parameters that I can run through (first do freq shift, then ...) and a way at each step to know when I've got it right. I don't know if this exists. Any suggestions would be great.

  I apologize if this is called something specific that I didn't search for - I'm new to the lingo. If it is called something specific, let me know and I'll happily search for that.

  Thanks!


Brian

  • 0
    TI__Guru**** 317180 points

    - If you set the CC1101 in asynchronous serial mode you can monitor the data out on the GDO pin with a scope and measure the distance (datarate) on the received bit train. I haven't tried this with CC1101 but it works well with CC1120 since when in transparent mode only the sign of the deviation is used.

    - If you access to a spectrum analysator it's possible to find the deviation by looking at the received spectrum. Or you can try to change the deviation step by step. Typically start with a deviation equal to half the datarate and go from there. This shouds be done in synchronous mode.

  • 0 in reply to TER
    Prodigy 60 points

    Cool - thanks!
    I will give it a try.

    I'm trying to figure out the differences between asynchronous and synchronous modes - is there a good place in the docs to look for an explanation of this?


    Thanks!


    Brian

  • 0 in reply to Brian White1
    TI__Guru**** 317180 points

    The CC1101 documentation has a separate chapter about asynchronous and synchronous modes.

    Simplified: For asynchronous  mode the chip has no knowledge about datarate and deviation (for Rx). When the deviation is larger than 0, a logic '1' is on the output else a logic '0' is on the output. 

    Synchronous mode is close to be the same as FIFO mode, the main difference is that the data is placed on a GDO and not in the FIFO.

  • 0 in reply to TER
    Prodigy 60 points

    Thank you very much; I will give it a try.

    All the best

    Brian