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CC3220MODA: Tx power measurment

Part Number: CC3220MODA
Other Parts Discussed in Thread: SYSCONFIG,

Hello all,

My used tools:
- CCS 10.2.0; Compiler TI V20.2.5.LTS
- SDK cc32xx_sdk_4_40_00_07
- SysConfig 1.8.0
- XDCtools 3.62.0.08

I took a signal output measurement of a customer specific board.
Because I am not an HF-Boy ;) I have some problems in understanding the result.
The board is on the measuring table. It is not built into a housing.

The application is based of the network terminal example.
In contrast to that it avoids any input, didn't wait before calling the radioTool_TxStart.
The process of continuous sending is never stopped.
The sources of test program used are attached to this ticket (only the pins for the LED and the UART are configured).

radiotool_channel6.zip



The function radioTool_TxStart is called with the following parameters:

i32_Result = radioTool_TxStart(
    e_TxMode,                  // TxMode_Continues
    e_Channel,                 // 6
    e_RateIndex,               // SL_WLAN_RATE_1M
    e_Preamble,                // Preamble_longMode
    e_DataPatternIndex,        // DataPattern_all_1
    u8_TxPower,                // 0, PowerLevel_HighGainStep_7
    u16_PacketSize,            // 24
    u16_PacketAmount,          // 1000U
    u32_DelayPeriod,           // 1
    u8_OverrideCCA,            // 1
    e_SlTxInhibitThreshold_e,  // u32_DelayPeriod
    i8_Tone,                   // 0
    au8_DestMac);              // {0x01, 0x23, 0x45, 0x67, 0x89, 0xAB}


The data sheet SWRS206E – MARCH 2017 – REVISED MAY 2021 of the CC3220MODA module states for the Wi-Fi TX power:
* 17.0 dBm at 1 DSSS
* 13.5 dBm at 54 OFDM

Because I can only measure in dBuV I used a webtool that translates the value 17dBm to 124 dBuV.





* module sends continuously (picture measure01.png):
* carrier around 2437 MHz (channel 6)


Unexpected:
But the power is less than expected. I can't see the expected power around 124 dBuV. At best I see peaks of around 90 dBuV.

What's going wrong in my case?
Perhaps settings OverrideCCA=1 and SL_WLAN_RATE_1M are the cause of my unexpected result?

Any suggestion is very welcome.

Best regards,
Roman

  • Hi Roman,

    17dBm is the conducted measurement of the device's output power.

    Since you are using a CC3220MODA, my assumption is that you are doing radiated measurements. If this is the case, there will be free space path loss and you will measure a lower output power. 

    Also, using the Radio Tool GUI is the preferred method to experiment with SimpleLink device's radio.

    BR,

    Seong

  • Hi Seong,

    many thanks for your information. Using a conducted measurement gives higher values.

    If I calculate my results back I am a little bit shocked about such a big difference (o.k. it is log).

    Is there anybody else, reading this topic,  who did the same measurement?
    Does anybody know, what values of Tx power I can expect for real - "wireless" Tx measurement of that module?

    Best regards,
    Roman

  • Roman,

    Radiated measurements will vary depending on the environment of the test bench and distance between the transmitter and receiver.

    What you can you do is add the gain of your antenna to the conducted TX power measurement to calculate the EIRP.

    If you don't mind sparing a few modules, you can cut the RF trace right before the PCB antenna and solder a pigtail cable to measure conducted power. See section 6.2.1 in the Antenna Selection appnote.

    BR,

    Seong

  • Hello,

    thanks for your answer. A second, more complete measurement with a much smaller distance between the receiver and the transmitter shows better results.

    Many thanks and best wishes,
    Roman