large amplitudes. With any signal, as the input level is increased beyond the linear range of the amplifier, gain compression will occur. A transistor's operating point may move with temperature, so higher power output may lead to compression due to collector dissipation. But it's not a change in gain; it's non-linear distortion. The output level stays relatively the same as the input level goes higher. Once the non-linear portion of the transfer characteristic of any amplifier is reached, any increase in input will not be matched by a proportional increase in output. Thus there is compression of gain. Also, at this time because the transfer function is no longer linear, harmonic distortion will result. Intentional compression In intentional compression (sometimes called automatic gain control or audio level compression) as used in devices called 'dynamic range compressors', the overall gain of the circuit is actively changed in response to the level of the input over time, so the transfer function remains linear over a short period of time. A sine wave into such a system will still look like a sine wave at the output, but the overall gain is varied, depending on the level of that sine wave. Above a certain input level, the output sine wave will always be the same amplitude. The output level of Intentional compression varies over time, in order to minimize non linear behavior. With gain compression, the opposite is true, its output is constant. In this respect intentional compression serves less of an artistic purpose. Radio-frequency compression Gain compression in RF amplifiers is similar to soft clipping. However, in narrowband systems, the effect looks more like gain compression simply because the harmonics are filtered out after amplification. Many data sheets for RF amplifiers list gain compression rather than distortion figures because it's easier to measure and is more important than distortion figures in nonlinear RF amplifiers. In wideband and low-frequency systems, the nonlinear effects are readily visible, e.g. the output is clipped. To see the same thing at 1 GHz, an oscilloscope with a bandwidth of at least 10 GHz is needed. Observing with a spectrum analyzer, the fundamental compressed and the harmonics picking up. Examples of RF compression A low-noise RF amplifier, if fed by a directional antenna to a consumer 900 MHz receiver, should improve the transmission range. It works, but the receiver may also pick up a couple of UHF stations