> Naively, I assumed that it must take more power to transmit than to receive, which is true on an instantaneous basis, but false on an average basis.
Even that is not necessarily always the case in low-power systems, since often receive amplifiers need to be run at a fairly high current to achieve a low noise floor, and power saving tricks like envelope tracking power supplies are harder to implement on the receive side.
For example, I've seen several Bluetooth LE radios where the instantaneous supply current is higher during receive than during transmit.
Even that is not necessarily always the case in low-power systems, since often receive amplifiers need to be run at a fairly high current to achieve a low noise floor, and power saving tricks like envelope tracking power supplies are harder to implement on the receive side.
For example, I've seen several Bluetooth LE radios where the instantaneous supply current is higher during receive than during transmit.