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CC1120DK Long Range Issue

Other Parts Discussed in Thread: CC1120, CC1101

Hi,


1) I have tried PER test with

-868 & 915 MHz Freq.,
-1.2kbps data rate,

- 14db tx Power

- tx Height 15m and rx Height 1.2m

but I am getting range of 250-300m only.


2) Also tried LRM demo

with 470 & 868 Mhz freq.,

tx Height 15m and Rx Height 15m

still I am getting range of 00-400 m only.


How can I achieve range of at least 4km ??

Is there any kind of register setting in CC1120 that we need to do to achieve range?

TIA

  • Hi,I presume you are using TI development kit.
    When you are using narrowband (1.2KBPs), you need to have high accuracy crystals on both Transmit and reciver boards. Otherwise, the tranmitter and receiver has a frequency offset in between them and this freq offset should be accomodated in the Rx Filter Bandwidth.
    I suspect the problem with the frequency offset in between the transmitter and receiver. This can be tested by increasing the Rx Filter Bandwidth on the receiver to around 100KHz (for test purpose). If the range improves with widening the filter then the problem with the accuracy of crystals on the boards.
    Also please make sure that the Antennas on the board makes a good contact with the SMA connectors. Sometimes the Pin on the Whip antenna is not making contact with the SMA.
    4KM range is possible with Line-Of-Sight only (without any obstructions in between them).
    Thanks,PM
  • Hi,

    Thank you for your quick response.

    Still having Issues.

    1) How can I find the accuracy of crystals on the board?

    2) How to make sure that SMA connectors are having good connection with antenna?

    Here are the scenarios I tried

    CC1120 Performance Line Development Kit test scenarios
    SW code Frequency Tx Height Rx Height Tx Power Deviation Data Rate Rx Bandwidth Range
    PER Test 868 MHz 15m(on terrace) 1.2m (On the Ground) 14dbm 4kHz 1.2kbps 25kHz 250m
    PER Test 915 MHz 15m(on terrace) 1.2m (on ground) 14dbm 4kHz 1.2kbps 25kHz 250m
    Long Range Mode test 868 MHz 15m(on terrace) 1.2m (on ground) 14dbm 1.499176 600bps 12.5 400m
    Long Range Mode test 868 MHz 15m(on terrace) 1.2m (on ground) 14dbm 1.499176 600bps 100kHz 450m
    Long Range Mode test 470 MHz 15m(on terrace) 1.2m (on ground) 14dbm 1.499176 600bps 7.81250 400m



    As you can see, I am not able to achieve range more than 500m and there were no obstacles between Rx and Tx in any of the scenario.

    Also tried dense urban environment city scenario given in this document section 5.3 still getting the 300m of range.

    http://www.ti.com/lit/an/swra479/swra479.pdf

    Can you suggest me any configuration to achieve range more than 1 km?

    Thanks,

    Maulik

  • Hi,

    It seems you don't have a problem with Antenna connections. If you have a problems wth Antenna connection, it won't get 400 Meters range.

    If I look at your results of Long Range Test at 868 MHz with 12.5KHz Filter BW and 100KHz Filter BW, it shows 400 meters with 12.5KHz BW and 450 meters with 100KHz BW. Theoritically, with 12.5KHz BW, the range should be more than double than the range with 100KHz BW in LOS but you get less range with 12.5KHz BW. This shows that you have a frequency offset in the Transmit and Receive boards.

    The frequecy offset can be verified by measuring the Transmit carrier frequecy ( in CW-Unmodulated mode) on both boards. You need spectrum analyzer or Frequency counter to measure the transmit frequency of each board. If their frequency is not the same then you need to offset one of the board frequency (programmed freq - for example 868.xxxx) to match it to the other. The frequecy accuracy is very important in narrowband application.

    Once you measure and correct the frequency offset then you can try again with 600bps, 1.5KHz Dev, 8KHz BW. You should get the maximum possible range with this setting.

    The range is also affected, if you have a stronger interferer signals (other than desired) at the receiver.

    Thanks,

    PM

  • Hi,

    We don't have Spectrum analyzer or Frequency counter. We are thinking to purchase it.

    Found one from ti

    http://www.ti.com/tool/msp-sa430-sub1ghz#1

    Can you please tell us that will it be appropriate for CC1120 (Sub 1GHz Band) ?

    Will this help us to get accurate frequency offset?

    If not, can you please suggest other options if available?

    Thanks,

    Maulik

  • Hi,

    I think the the minimum frequency resolution is around 400Hz (Not clear) on that spectrum analyzer. By considering the cost of the spectrum analyzer, it is good for coarse measurements.

    So, for 12.5KHz BW, 400Hz error should be OK.

    Please make sute that the spectrum Analyzer has enough frequency resolution before you buy it.

    Thanks,

    PM

  • This will help to show a rough frequency offset until you have a standard spectrum analyzer. The minimum span of the 430 spectrum analyzer is 100 kHz.

    The 430 spectrum uses CC1101 radio so this will cover the standard sub 1 GHz frequency bands.

    //Richard
  • If you don't have an accurate spectrum, use a CC1120 board with a TCXO as a measuring receiver. Sweep the frequency in fine steps and see for which frequency the RSSI is best.
  • Hi,

    Thanks a lot for your suggestions.

    We found offset as you have mentioned,

    CC1120 as a measuring device and sweep the frequency in fine steps and found frequency offset.

    Now we are able to get 1-1.2 km range in dense environment at 868MHz Freq., 600bps data rate, 1.499176 Freq. deviation, Tx height-15m and Rx height-1.2m(In hand).


    Thanks,

    Maulik