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CC1120 never receives anything

Anup Rajput
Expert 1920 points
Other Parts Discussed in Thread: MSP430FR5739, CC1120

Hi,

We are working on a test setup based on a combination of an MSP430FR5739 Launchpad (which comes with EM slots) + PCBs we got manufactured from the Gerber provided for CC112x (CC112x 2 layer design with IPC - http://www.ti.com/tool/cc112x-ipc-2l-868rd). The parts used are the same and the Balun is the one from Johnson.

We were able to port the Easylink example to the same board, and run with default values. On the transmitter side, we see that the interrupt on successful transmission is raised. But, the receiver side never receives anything!

We have experimented with the on-board PCB antenna but found out that the PCB thickness is wrong (should have been 0.8mm, but it was manufactured using 1.6mm). Now, we have moved to SMA connector + whip antenna. But, results are the same! We have never been able to get anything on the Rx side.

Although we have tried multiple settings in the SmartRF Studio, the current one that we are trying is:

Carrier Freq.: 868.00 MHz

Xtal Freq.: 32.00 MHz

Symbol Rate : 50 ksps

RX filter BW: 100.00 kHz

Modulation format: 2-FSK

Deviation 24.963379 kHz

TX power: 15dBm

Manchester Enable: NO

PA ramping: YES

Whitening: NO

Performance Mode: High Performance

Any guidance on how to go about this would be great!

  • 0 in reply to Anup Rajput
    TI__Mastermind 39860 points
    Seems like the first thing you are trying to do is to set up an RF link. This is not how to do RF testing and debugging as you then have no way of kopwing where the problem is; could be HW/RF, antenna, SW

    Check your HW: Test RX and TX conducted performance first. Solder a semi-rigid coax to the board at the antenna feedpoint. Remove any connectoins to the PCB antenna. Use a spectrum analyzer to measure the TX performance. Use an RF signal generator to measure the RX performance www.ti.com/lit/swra097 explains how to do simple sensitivity measurements. Use SmartRF Studio to control your board (this is a good known SW) by soldering wires to the SPI and GDO lines and connect to TrxEB. After doing this testing and doing whatever tuning needed you know the HW is ok.

    Check your antenna: Measure the S11 using a network analyzer. Tune the antenna length and/or improve the antenna impedance matching. www.ti.com/lit/swra161 tells you what and how to test. After doing this test you know the antenna performance is ok.

    Then, when HW and antenna are tested and verified, you can test with your SW. Not before.
  • 0 in reply to Sverre
    Expert 1920 points

    Hi Sverre,

    For lack of certain resources, we decided to go with TI's Gerber files instead of designing our own PCB. Would we still have to go through this whole process? We thought that the whole point of getting the Gerbers from TI was to bypass verifying the hardware itself!

  • 0 in reply to Anup Rajput
    TI__Guru**** 317180 points
    The same still applies to some degree since it could be something wrong in assembly or similar.

    I notice that you have started with sniff mode in Rx, if you use "normal" Rx do you then receive anything? Also have you tried to use cont Rx and reading out the RSSI to see if something actually is in the channel.
  • 0 in reply to TER
    Expert 1920 points
    Hi TER,

    We tried the regular Rx mode too. While we never receive any packet (indicated by the interrupt on GPIO), reading the MARCSTATE register confirms that the CC1120 stays in Rx mode, and reading the RSSI0 and RSSI1 registers shows that the RSSI seems to always be valid, as is the CARRIER_SENSE_VALID bit, while the CARRIER_SENSE bit is almost always '1' and rarely goes to '0'. The RSSI bits when concatenated and shifted right appropriately, result in a reading of 23, but I don't think it is of any relevance.

    Please note that this is WITHOUT the transmitter being switched ON. Behavior remains the same even when the transmitter is switched ON.

    Does this indicate that there is some sort of noise on the carrier frequency?
  • 0 in reply to Anup Rajput
    TI__Guru**** 317180 points
    Do you have a TRXEB or a CCDebugger? For debugging it would be nice to be able to control the board with SmartRF Studio.

    As for the carrier sense bit, have you tried different frequencies and also tried to change the carrier sense threshold?