Wifi chip transmits when monitor mode is enabled

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JeBl_3106276
Level 1
Level 1

I have made an application in WICED SDK that uses the monitor mode functionality. I have noticed that whenever monitor mode is enabled (or if the channel is changed during monitor mode) the chip transmits a "narrow band"  signal with a duration of approximately 30-40 ms. I've boiled things down to the following simple application

void application_start( )

{

    wiced_init( );

    wwd_wifi_set_channel(WICED_STA_INTERFACE, 6);

    while (1) {

        wwd_wifi_enable_monitor_mode( );

        wiced_rtos_delay_milliseconds(200);

        wwd_wifi_disable_monitor_mode( );

    }

}

Every time wwd_wifi_enable_monitor_mode is called a high powered narrow signal is transmitted. In the test code above channel 6 (2437.0 MHz) is set prior to toggling monitor mode. In this case the narrow band signal appears at 2439.0 MHz as seen in

Screen_0046.png

Switching to zero span on 2439.0 MHz shows the time aspects of the signal

Screen_0044.png

Every time monitor mode is enabled (in the test application this i every 200 ms) these transmit signal can be observed. The measurements are done radiated on a CYW943907AEVAL1F board.

How can I avoid this? These high powered CWs should not be there - my application should never transmit anything.

Is it possible to completely disable the TX path of the module?

I'm using:

board: CYW943907AEVAL1F

WICED SDK version: 006.002.001.0002

Any pointers on how to avoid this are much appreciated.

/Jesper

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1 Solution
Zhengbao_Zhang
Moderator
Moderator
Moderator
250 sign-ins First comment on KBA 10 questions asked

Hi:

   You can have a try on below setting:

1.  wwd_wifi_set_down

    set monitor

     wwd_wifi_set_up

2.  turn off roam

  wwd_wifi_turn_off_roam

3.  wwd_wifi_set_scan_suppress , disabled.

4. if possible,  please help to capture one sniffer log in your area.

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2 Replies
Zhengbao_Zhang
Moderator
Moderator
Moderator
250 sign-ins First comment on KBA 10 questions asked

Hi:

   You can have a try on below setting:

1.  wwd_wifi_set_down

    set monitor

     wwd_wifi_set_up

2.  turn off roam

  wwd_wifi_turn_off_roam

3.  wwd_wifi_set_scan_suppress , disabled.

4. if possible,  please help to capture one sniffer log in your area.

Hi zhez

Using wwd_wifi_set_up/down solved this issue, Thanks.

Also if the channel needs to be changed during monitor mode wwd_wifi_set_down/up should surround the call to wwd_wifi_set_channel.

/Jesper

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