A transmitter comprising: a predistortion sub-system; a power amplifier; an undersampling observation receiver configured to: receive a concurrent multi-band signal output by the power amplifier, the concurrent multi-band signal having a plurality of original frequency bands; undersample the concurrent multi-band signal at a select sampling rate to provide an undersampled multi-band signal, wherein the select sampling rate is based on carrier frequency values and corresponding bandwidth values for the plurality of original frequency bands of the concurrent multi-band signal such that a frequency-flipped image of at least one of the plurality of original frequency bands of the concurrent multi-band signal and images of any remaining original frequency bands of the plurality of original frequency bands fall within a frequency range of zero to half of the select sampling rate and do not overlap one another; and process the undersampled multi-band signal to provide a plurality of feedback signals for the plurality of original frequency bands of the concurrent multi-band signal, each feedback signal of the plurality of feedback signals corresponding to a different one of the plurality of original frequency bands; and an adaptation sub-system configured to adaptively configure the predistortion sub-system that is configured to compensate for non-linearity of the power amplifier based on the plurality of feedback signals, wherein the undersampling observation receiver comprises a signal processor (60, 96) which is configured to, for each original frequency band of the at least one of the plurality of original frequency bands: determine whether a frequency-flipped image for the original frequency band falls within the frequency range; based on the determination, downconvert the frequency-flipped image for the original frequency band in the frequency range of zero to half of the select sampling rate to baseband to provide a frequency-flipped baseband feedback signal for the original frequency band; and provide a complex conjugate (64; 100) of the frequency-flipped baseband feedback signal for the original frequency band as a baseband feedback signal for the original frequency band. receive a concurrent multi-band signal output by the power amplifier, the concurrent multi-band signal having a plurality of original frequency bands; undersample the concurrent multi-band signal at a select sampling rate to provide an undersampled multi-band signal, wherein the select sampling rate is based on carrier frequency values and corresponding bandwidth values for the plurality of original frequency bands of the concurrent multi-band signal such that a frequency-flipped image of at least one of the plurality of original frequency bands of the concurrent multi-band signal and images of any remaining original frequency bands of the plurality of original frequency bands fall within a frequency range of zero to half of the select sampling rate and do not overlap one another; and process the undersampled multi-band signal to provide a plurality of feedback signals for the plurality of original frequency bands of the concurrent multi-band signal, each feedback signal of the plurality of feedback signals corresponding to a different one of the plurality of original frequency bands; and an adaptation sub-system configured to adaptively configure the predistortion sub-system that is configured to compensate for non-linearity of the power amplifier based on the plurality of feedback signals, wherein the undersampling observation receiver comprises a signal processor (60, 96) which is configured to, for each original frequency band of the at least one of the plurality of original frequency bands: determine whether a frequency-flipped image for the original frequency band falls within the frequency range; based on the determination, downconvert the frequency-flipped image for the original frequency band in the frequency range of zero to half of the select sampling rate to baseband to provide a frequency-flipped baseband feedback signal for the original frequency band; and provide a complex conjugate (64; 100) of the frequency-flipped baseband feedback signal for the original frequency band as a baseband feedback signal for the original frequency band. determine whether a frequency-flipped image for the original frequency band falls within the frequency range; based on the determination, downconvert the frequency-flipped image for the original frequency band in the frequency range of zero to half of the select sampling rate to baseband to provide a frequency-flipped baseband feedback signal for the original frequency band; and provide a complex conjugate (64; 100) of the frequency-flipped baseband feedback signal for the original frequency band as a baseband feedback signal for the original frequency band.