range test

[mogplus8]

Hi, I am thinking of using the nrf24l01 board from Banggood ([here]) to build a transmitter/receiver set for r/c model planes. However one of the things I would like to do is implement a range check function. On most commercial transmitters there is a setting that reduces the output power of the transmitter by about 90%. In this state the operator walks away from the model (usually about 40-50 paces) and checks that the radio is still working (or checks the RSSI if it is a telemetry radio). If all is okay he can be fairly confident that the range is okay. My question is, is it possible to reduce the output power of the nrf24l01 chip by software control somehow, or maybe by reducing the voltage provided to the board? I'm happy to experiment and find a suitable value for voltage or whatever may be required to reduce the power, but just wondering if it's possible, and if such a test would be valid? Thanks, Ian PS I couldn't figure out how to add tags, sorry.

[ovrebekk]

Hi

First off you should double check if you have the nRF24L01, or the newer nRF24L01+/nRF24L01p Most modules today should use the newer chip (both chips were released about 10 years back).

Both devices have the following output power settings: 0dBm, -6dBm, -12dBm and -18dBm

Each reduction of the output power by 6dB should reduce the range by a factor of 2. In other words, going from 0dBm to -18dBm should reduce the range by a factor of 8 (approximately).

To change the output power you should write to bits 1 and 2 in the RF_SETUP register (for more details, refer to the nRF24L01+ datasheet).

Reducing the supply voltage will not affect range, it will simply stop working if you go below the allowed supply range ;)

[mogplus8]

Thanks for the quick reply. The board does have the NRF24l01+ chip according to the description on Banggood.com, so that's good. Reducing by a factor of 8 is useful. That would indicate that, if it's still working 40m away in "low power" mode, it should work 320m away in normal power mode. The range is claimed to be up to 1000m, but realistically, for my application, 320m should be more than enough. I rarely fly more than about 200m away anyway, because the plane gets too hard to see if it's too far away! Thanks, Ian

[ovrebekk]

1000 meters is quite impressive, but if they have a PA on the board I am sure it's possible :)

Because of the PA it's hard to predict the range at the different power settings, but if you do some experimentation you can probably find an estimate. If you are unlucky the PA will compensate for a lower output power of the nRF24L01+ by turning up the gain, which would reduce the impact of changing the TX output power (compared to using the nRF24L01+ without a PA).