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CC1101 Range and FEC

Johan Wallström
Intellectual 335 points

Other Parts Discussed in Thread: CC1101

Hello,

I'm designing a product using the CC1101 transceiver. 

I can currently receive at a range of about 60 meters. I need to push this up a bit.

I was thinking that if I enable the FEC/Interleaver, the range would increase, however

it turned out it would actually decrease. Same thing if I turn down the baudrate.

Would this indicate that the crystals are not enough accurate enough?

I have a log of the received data of a typical message with and without FEC, as well as the parameter settings,

visible in the screenshots here: edab.nu/flextag. The start and end of a message is shown with the cursor markers.

  • 0
    TI__Mastermind 39860 points

    Without knowing your system parameters (RF frequency, data rate, deviation, RX filter BW and modulation format) I will still say that 60 meter range (line-of-sight?) is lower than what you should expect. FEC will not improve range dramatically (at least not for short packets) so I suggest you look at the design first of all. If you provide schematic and gerbers we can have a look. Also, before you set up an RF link you need to measure conducted RX and TX performance separately to get an idea why the range is poor. Is the sensitivity lower than you should expect? is the output power lower than you should expect? For the former use a signal generator as input. For the latter use a spectrum analyzer. What about the antenna performance? You also need to measure this separately before setting up an RF link. Use a network analyzer and check S11 and resonance frequency. 

    If your first test is an RF link you have no way of knowing where the problem is. In order to debug you have to narrow down the problem => separate RX, TX and antenna testing

  • 0 in reply to Sverre
    Intellectual 335 points

    Thank you for your suggestion. I will see what tools I can bring up to examine these areas. Since this is my first radio project I do not really know what levels I would expect. The RSSI shows around -30 when the devices are close to each other. 

    So it's a 868 MHz. The data rate is not set, at the moment I am trying with 200kHz. Deviation is 47kHz. The details are available in the parameter settings screenshot. It's currently set to GFSK.

    I have added schematics and placement including the antenna layout in the folder (edab.nu/flextag). Is it enough or is a gerber file preferred?

  • 0 in reply to Sverre
    Intellectual 335 points

    I've added the gerber zip in the folder too. I can add protel files if requested.

  • 0 in reply to Johan Wallström
    TI__Mastermind 39860 points

    The register settings you provided are for 160 kbps, +/-47 kHz deviation. This is ok. However, you still need to make some register changes:

    AGCCTRL2 = 0xC7 (Setting AGCCTRL2][2:0] = 0 will not work as this will give a too low SNR for low input levels)

    FREND1 = 0xB6

    MDMCFG2 = 0x13 (optimized for sensitivity, not current consumption)

    Haven't look at the design files, but suggest you try the register changes first and report back.

  • 0 in reply to Sverre
    Intellectual 335 points

    Hello,

    Thanks a lot for the information! It really hit the spot and the range increased a lot, so far I could test up to 100 meters with a low percentage of errors. I will continue testing longer ranges soon.

  • 0 in reply to Sverre
    Intellectual 335 points

    I thought that my settings would produce a data rate of 200kb/s, as in:
    MDMCFG4 = 0x5C
    MDMCFG3 = 0xF8
    DRATE_E = 12
    DRATE_M = 248

    R_DATA = (256+248) * 2^12 / 2^28 * 26MHz = 200kHz.

    This seems to be what I get in reality too.

  • 0 in reply to Johan Wallström
    TI__Mastermind 39860 points

    Sorry - my mistake. MDMCFG5 = 0x5C and MDMCFG3 = 0xF8 corresponds to 200 kbps (I entered MDMCFG3 = 0x93 when I did the calculations).  

  • 0 in reply to Sverre
    Intellectual 335 points

    May I also ask if it is acceptable to run the device on 2.1V to reduce current consumption? We were somewhat hesitant reading the datasheet.

  • 0 in reply to Johan Wallström
    TI__Mastermind 39860 points

    Don't understand your concern. CC1101 is characterized down to 1.8V supply voltage.

    In RX there will be less than 1 mA difference in current consumption across the supply voltage range as the RX path runs on regulated voltage (i.e 1 mA difference between 3.6 and 1.8 mA supply).

    The output power and TX current vs supply voltage is given in the CC1101 data sheet (Table 5 and Table 11)