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CC1200: Poor range test results using SmartRf default settings

Spiros Kleftogiannis
Prodigy 130 points
Part Number: CC1200
Other Parts Discussed in Thread: CC2538, , TEST2, CC-ANTENNA-DK2

Hello all,

I'm working in a custom board using cc2538 for zigbee and cc1200 at 169MHz connected to cc2538 over spi.

The cc1200 has an external PA - 65367_11 Skyworks - up to 27dBm Tx power, no diversity, SMD antenna -2dB Peak Gain.

My problem is that even with Smart RF Studio default settings (Generic 169MHZ, Symbol rate: 1.2kbps, 2-FSK, 12.5 kHz, 10.9 Rx Filter BW) & Tx power at 27dBm,

I cannot get a link greater than 400 meter in Packet tests.

Also the best RSSI I can get without packet loss is around -90dBm.

Using a spectrum analyzer the noise floor in my area is around -100dBm.

On my tests, my devices are 1.5 meter from ground.

Could anyone help me on this?


Thanks in advance,

Spiros

  • 0
    TI__Guru**** 317180 points
    - The default settings you refer to need very small frequency offset between the boards. Either compensate for the frequency offset or increase the Rx Bw to 25 kHz.
    - In the excel sheet in this post: e2e.ti.com/.../375556 you will find a check list for debugging poor range. Go through this and post the measurement results.
  • 0
    TI__Mastermind 29560 points

    Hi,

    The antenna bandwidth at 169 MHz is very small and this is easily detuned. Which antenna are you using ?

    Regards,

       Richard

  • 0 in reply to RGW
    Prodigy 130 points
    Hello all & thank you for your replies!

    I've make some tests using/including the default RF settings in my code and 27dBm Tx power:

    Test1:
    Using my board connected-to / powered-by a laptop, I'm sending a "ping" message to another board powered by a portable battery-pack.
    In this setup, I manage to reach only 80 to 100 meter line-of-site.
    The worst RSSI I could get was about -67dBm, then nothing.

    Test2:
    Both board are connected to 2 different portable laptops.
    In this setup, I manage to reach about 850 meter line-of-site!!!
    The worst RSSI I could get was about -107dBm.

    More or less I had the same results with external antenna (+2dB gain) & with smd AP-1010a antenna (-2dB gain).
    According to my results, this is definitely not a firmware issue (I think) .
    Please, do you have any idea what could be the issue?

    Regards,

    Spyros
  • 0 in reply to Spiros Kleftogiannis
    TI__Guru**** 317180 points
    Did you look at the excel sheet I pointed to?

    Which datarate/ settings do you use?

    Since Test1 and Test2 gives very different results you have to look into what you do differently in the two tests.
  • 0 in reply to TER
    Prodigy 130 points
    I've looked it & thank you for that.
    From Smart RF I'm using : "Typical Settings" -> "Generic 169MHz" -> "Symbol rate: 38.4kbps. 2-GFSK, RX BW 100kHz, ETSI Standard (169MHz)"
    Based on those settings, I change:
    Carrier Frequency: 169.40625MHz, RX Filter BW: 11.76kHz, Symbol rate: 4.8ksps, deviation 2.4kHz.
    As i said above with exactly the same settings, I take different results when the one of the boards powered by a battery-pack or powered by a laptop usb port!
    How (or can) a usb port/ground of a laptop effect the performance?
  • 0 in reply to Spiros Kleftogiannis
    TI__Mastermind 29560 points
    The SMD antenna (AP-1010a antenna, 2.5 x 1.2 x 0.08 cm) will not have a gain of -2 dB unless the GND plane of the antenna test board is very large.

    The large 169 MHz antenna on the CC-Antenna-DK2 that is 8 x 8 x 3 cm only has an efficiency of -6 dB. A whip antenna approx 30 cm long and tuned on a small GND plane will have an efficiency around -6 dB and a gain of -2 dB.

    CC-Antenna-DK2: www.ti.com/.../swra496.pdf

    Calculate with a realistic antenna efficiency on the GND plane size of your product.
  • 0 in reply to RGW
    TI__Guru**** 317180 points
    Spiros: You wrote that Test1 send back a ping, does that mean that Test1 and Test2 runs the same software or not?

    You wrote that you are sending 27 dBm. Are you powering this in Tx from the batterypack? (27 dBm means 400 -500 mA current draw)
  • 0 in reply to TER
    Prodigy 130 points
    TER: I've been monitoring the power from the battery-pack and it gives the power the board need for transmission (450mA) when needed.
    About the software, it is the same in both tests: One board sends a ping command to the other, & the second board replies with the RSSI value it senses from "ping request". So in my software I have the RSSI values from both devices.
    Richard: Thanks for the suggestion, I will check the GND-plane & reply back.

    Thank you both again for your quick responses!