• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 54 subscribers
  • Views 666 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

CC1200 4FSK at maximum rate

Bill Garland
Prodigy 250 points
Other Parts Discussed in Thread: CC1200

I am trying to use the CC1200 using the RF Studio '500ksps, 4GFSK .. ETSI' settings. The link works most of the time but I get occasional CRC errors. These are nearly always on the first payload byte (which in my case is the packet length byte).

The error seems to be consistent in that bit 6 of the byte gets set to 1. This suggests the first 4FSK symbol after SYNC is decoded as 01 rather than 00.

Is this a known problem?

Bill

  • 0 in reply to Sverre
    Prodigy 250 points

    Hi Sverre

    I tried changing the AGC_REF as suggested in the link but it makes no difference.

    Bill

  • 0 in reply to Bill Garland
    TI__Mastermind 39860 points

    The modulation index (for the inner symbols) might be too low. Have you tried increasing the deviation?

    Try to increase the deviation from 400 kHz to 500 kHz (or more) and see if this helps. Change DEVIATION_M to 0x9A for 500 kHz deviation, DEVIATION_M = 0xC3 for 550 kHz deviation,DEVIATION_M = 0xEC for 600 kHz deviation Note: since the RX filter BW is 1.7 MHz the deviation should not be increased above 600 kHz in order for the transmitted signal to fit into the RX filter BW and also allow for some crystal inaccuracies between RX and TX units.

    AGC settings to look at are AGC_CFG1.AGC_WIN_SIZE and AGC_CFG1.AGC_SETTLE_WAIT. If you increase those settings you should also test with a longer preamble.

    Provided "wrong link" in previous post: This one is more detailed: http://e2e.ti.com/support/wireless_connectivity/f/156/t/362128.aspx

     

  • 0 in reply to Sverre
    Prodigy 250 points

    I have tried a number of 4 GFSK configurations (both high and low bandwidths and deviations) using two CC1200 dev boards and cannot achieve a 100% reliable link under good SNR conditions. 

    The settings seem to be very sensitive to deviation. If I vary the receiver deviation slightly (compared with the transmitter) the link fails. The receiver is also sensitive to the Viterbi setting. The problem goes away when I use 4 FSK but this is not an option as the spectrum is too wide.

    I would be interested to know how the receiver works in 4 GFSK mode. I believe that the Gaussian filter will close the 'eye' which is OK for 2GFSK but for 4GFSK this moves the 'decision window'. Does the Viterbi compensate for this? 

    On a related subject, I am confused by the eye diagrams in SWRS123B. The 2 GFSK diagram looks more like 2 FSK