Zigbee RSSI is lower when PA/LNA is activated

[sjf]

Hi,

I'm testing a couple of EVBT840X boards from Fanstel which includes a PA + LNA within the nRF52840 module.

The source code is based on the ble_zigbee_dynamic_template example.

I added these defines:

// Fasntel PA + LNA

#define APP_PA_LAN

#ifdef APP_PA_LAN
#define APP_PA_PIN      17
#define APP_LNA_PIN     19
#define APP_CHL_PIN	8
#define APP_CPS_PIN	6
#endif

And then I included the source code they provide in the datasheet (www.fanstel.com/.../EV-BT840F-User-Manual.pdf) and calling this piece of code at the very beginning of the main function:

#ifdef APP_PA_LAN 

    nrf_gpio_cfg_output(APP_CPS_PIN);
    nrf_gpio_cfg_output(APP_CHL_PIN);
    nrf_gpio_pin_set(APP_CHL_PIN);
    nrf_gpio_pin_clear(APP_CPS_PIN); //enable
    pa_lna_init(APP_PA_PIN,APP_LNA_PIN);
#endif	

Setting the Tx Power to +8dBm in all the cases and boards separated with the same distance, I perdiodically invoke the function zb_zdo_get_diag_data() to get the rssi value.

With PA+LNA DISABLED = -50 dBm
With PA+LNA ENABLED  = -70 dBm

-> What's wrong with this? Why the RSSI value is worst when the PA+LNA is enabled?
Note: I disabled everything related with bsp_leds and bsp_buttons

[Marjeris Romero]

Hi,

Can you try using an oscilloscope or a logic analyzator to trace the PA/LNA pins in evaluation board? Are you able to see if the LNA is actually enabled or not when you set its state in the code?

Looking at the source code in the datasheet it looks like pa_lna_init() doesn't seem to configure the LNA/PA pins for Zigbee, only for the Softdevice. 

[sjf]

Hi msromero,

But what else needs to be configured for Zigbee?

I thought that Softdevice was the only one that needs this extra configuration. Is that true?

Thanks

[Marjeris Romero]

Hi,

If you enable PA/LNA in Softdevice it will only take effect when the radio is running BLE. The nRF 802.15.4 driver has it's own API to manage frontend modules, see: https://infocenter.nordicsemi.com/topic/sdk_tz_v4.0.0/group__nrf__802154__frontend.html 

But I am not sure anyone has tested using both at the same time. I recommend you try out and use an oscilloscope of logic analyzator to trace the PA/LNA pins to make sure they are enabled for both protocols.

Best regards,

Marjeris