Regarding setting Tx power to +8dbm

[Ravi Theja]

Hi,

 I am using Nordic nRF52840 SoC with nRF5_SDK_15.2.0_9412b96(SDK) and S140 softdevice. I tried to set Tx power to +8dbm using 

rc = sd_ble_gap_tx_power_set(BLE_GAP_TX_POWER_ROLE_ADV ,m_adv_handle,+8); after calling advertising_init(); in ble_app_multipepripheral example.But when i see the RSSI signal in mobile using nRF connect for mobile app its showing maximum of -15dbm instead of +8dbm when i place the mobile near the device. The ret_code(rc) of this api sd_ble_gap_tx_power_set(BLE_GAP_TX_POWER_ROLE_ADV ,m_adv_handle,+8); is 0 when i printed which means NRF_SUCCESS.Can anyone please help me why its showing -15dbm instead of +8dbm?

[awneil]

Ravi Theja said:

when i see the RSSI signal in mobile using nRF connect for mobile app its showing maximum of -15dbm instead of +8dbm

Of course you won't see +8dBm !

"RSSI" = Received Signal Strength Indication - it is what your phone is receiving - not what the peripheral is transmitting!

[Ravi Theja]

Hi awneil,

When I place the mobile near the device, Mobile should receive almost the same signal strength transmitted by peripheral?

Is there any way to know whether peripheral is transmitting 8dbm signal or not?

[awneil]

There will always be losses. An RSSI of -15dBm sounds pretty good.

Ravi Theja said:

Is there any way to know whether peripheral is transmitting 8dbm signal or not

you would need a proper RF analyser.

Remember that the +8dBm figure is the output from the chip itself;  so it will be affected by your PCB layout, antenna, and antenna tuning - before it even leaves your board!

You can verify that you code is actually having an effect by changing between, say, +8 and -8 ...

[Ravi Theja]

Hi awneil,

 Is there any other to verify it without RF analyzer? because I don't have it right now.

yeah, there is a change in RSSI signal when I change the power setting from -8dbm to +8dbm.

[awneil]

Ravi Theja said:

there is a change in RSSI

That's the best you can do without proper test equipment.

But, to be honest, how will measuring the number help?

[Ravi Theja]

Ok awneil. Thank you.

My application requires Tx and Rx are 100m apart needs to be connected and data transmission should happen. But with current power setting Tx and Rx are not getting connected. So, I am trying to understand whether I am utilizing total Tx power or not.

[Hung Bui]

You don't need +8dBm for 100m distance if your device is properly tune and if light of sight, out door. +4dBm should be enough. Make sure you device is properly tuned. We would suggest you to test using our nRF52 DK. 

[Ravi Theja]

Hi Hung,

  If it supports 100m distance with +4dBm, then power requirements also less. Thanks for the suggestion. But my application requires devices may not be in the line of sight and surrounded by metals. So, I am thinking of using +8dBm to meet the requirements. Will +8dBm works for my application?

I don't have nRF52 DK right now. I will try to get it and test on it.