A method of characterizing a radio frequency traffic channel comprising a transmitter and a receiver. The method comprises calculating a first error rate associated with a sequence of bits sent by the transmitter at a first amplitude and received by the receiver. The first error rate is then used to determine a second amplitude to be used by the transmitter when sending a further sequence of bits. Subsequently, a second error rate associated with this further sequence of bits is calculated and compared to a target error rate. If this second error rate differs from the target error rate by more than a predetermined amount, a third amplitude is calculated which differs from the first amplitude by a lesser amount than the second amplitude differed from the first amplitude. Otherwise, the third amplitude is calculated which differs from the second amplitude by an amount determined by the second error rate.