Default Transmitter Output Power

[jschorey]

We are trying to determine the output power of the radio transmitter. We use it in a BLE mode. Our code doesn't seem to access any of the pertinent registers. Also, I don't see any calls we make to "sd_ble_gap_tx_power_set()", which is defined in ble_gap.h. The accepted values are: -40, -20, -16, -12, -8, -4, 0, and 4 dBm. The register says the default is 0 dBm. If our application makes no change, can we expect the default of 0 dBm? The 23.15.4 table in the data sheet notes that the typical setting is 4 dBm. Typical is not the default?

[Hieu]

Hi jschorey,

My apology for the long wait. It has been the Easter holiday, but we are now back to work.

I looked over a few SoCs which has the TX Power you listed, and my guess is that you are working with the nRF52832? 

If so, in table 23.15.4 of the nRF52832 Product Specification v1.8, the typical value is given for the "Maximum output power" property, not the typical TX Power of the device.

Hieu

[jschorey]

Thank you. I see "-20 to +4 dBm TX power, configurable in 4 dB steps" in the Key Features section. And I understand your point, "the typical value is given for the "Maximum output power" property, not the typical TX Power of the device." However, my question still remains: What is the default transmitter power setting if the user's App does not change it? It would appear to be 0 dBm. Would this be set in the softdevice? 

[Hieu]

Oh sorry, I didn't notice that part was also not clear.

The default for the SoC is 0 dBm. 

In the nRF5 SDK, if you don't explicitly change it otherwise, it will be 0 dBm. I am not sure if the SoftDevice set it again to 0 dBm, or if it just leaves the TXPOWER register unchanged.

As you mention the SoftDevice, I don't think you are using the nRF Connect SDK (NCS). However, just in case, please note that with the NCS, there is another concept also using the term "default." It is the default configuration for the application software. For BLE, it is configurable by the Kconfig CONFIG_BT_CTLR_TX_PWR. I am not sure how it is done in other protocols. If you need to know about the default when using NCS with other wireless protocols, please let me know..

[jschorey]

Thank you. That is very helpful.

[jschorey]

Hieu, I wonder if you could answer one other question... Do you know the approximate BLE open air transmit range at 0 dBm? 

[Hieu]

There is an old blog post on that topic here: https://blog.nordicsemi.com/getconnected/tested-by-nordic-bluetooth-long-range.

I am pretty sure the number there is recorded with a very idealistic environment though. I am not sure if that's what you mean by open air.

In a city or office environment, you will have a lot of radio interferences and obstacle. The range will be a lot smaller. It varies a lot based on the actual environment, which is likely why we won't find a lot of people dare making any claim on ranges outside of the ideal case.

[jschorey]

Understood. Thanks. I found this article handy, too, especially since we use Bluetooth 4 rather than 5.

blog.nordicsemi.com/.../things-you-should-know-about-bluetooth-range