Range of values for TX power

For the transmission power, are we allowed to use any number in the range [-30, 4] or only the values specified in table 37 in the product specification? When we select one of these values, what value do we use for the tx level in the advertising value? It isn't going to be the same value, is it? I'm confused, because according to my measurements with nRF 51822 Beacon kit, tx power at one meter is -54, which is clearly not in the aforementioned range.

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  • Hi Sarah,

    If you look in the documentation, this should be pretty clear. Only the values mentioned there is allowed.

    The TX power is a setting for the radio to set its transmitting strength. Higher values amplify the signal strength, but also increase power usage. The values you are measuring are received signal strength in dBm, which is based on the distance between the devices, the transmitting power of the advertiser, and the sensitivity of the peer. So while not entirely unrelated, these two values will be vastly different and should not be compared as such.

    The TX Power AD field should be set to the transmitting power of your advertiser, so either of the allowed values for sd_ble_gap_tx_power_set().

  • Okay, I was not aware of you using any manufacturer specific data at all, so please mention this in your question next time. Is this the iBeacon profile? If so, then the TX power is indeed included as the last byte of the data (in 2's complement form). The standardized way of including the TX power level is to use the AD Type, but this costs 3 bytes of advertising data. You might not need to include the standardized AD Type if you only care about peers that understand the iBeacon format.

    Advertising data is formatted like Length1|Type1|Data1|Length2|Type2|Data2|...| where DataN has a dynamic length based on the type. The define you list is meant for the Type field, not the Data field. I am not sure if the actual TX power levels have any defines.

    Just remember that new advertising data will not be effective until the next advertising event. TX power could change faster, so be careful!

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  • Okay, I was not aware of you using any manufacturer specific data at all, so please mention this in your question next time. Is this the iBeacon profile? If so, then the TX power is indeed included as the last byte of the data (in 2's complement form). The standardized way of including the TX power level is to use the AD Type, but this costs 3 bytes of advertising data. You might not need to include the standardized AD Type if you only care about peers that understand the iBeacon format.

    Advertising data is formatted like Length1|Type1|Data1|Length2|Type2|Data2|...| where DataN has a dynamic length based on the type. The define you list is meant for the Type field, not the Data field. I am not sure if the actual TX power levels have any defines.

    Just remember that new advertising data will not be effective until the next advertising event. TX power could change faster, so be careful!

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