Hello,
Is that possible to force carrier frequency out of 2.4 GHz band (modify canals) for a special underwater application (2.4 GHz is not adapted so i whish to move on another band but keeping nrf51 with bluetooth on 2 the 2 sides of the link) ?
Is there any way to use an external power amplifier to boost signal ?
Hi. No this is not possible. You can only change the carrier frequency to 2.5 GHz on the nRF51. You will need to go much lower than that to get any range at all under water.
Using a power amplifier to boost signals in air is possible though. Here is a relevant application note: Range Extension for Nordic nRF51 Series with RFaxis RFX2411N RFeIC
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