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As part of a test to determine its applicability to coaxial repeaters, a feedforward error-control system was applied to an L-4 coaxial system flat-gain amplifier operating in the frequency range of 0.5-20 MHz. The error amplifier was a duplicate to the main amplifier. With three test tones at 7.5 dBm output each applied within the last L-4 master group, modulation products in the uncompensated system were observed about 65 dB down from a single-tone level. With the error loop applied, modulation products dropped to greater than 100 dB over the range, often exceeding 110 dB. In particular, the third-order intermodulation product corresponding to A + B - C was reduced by 42 dB to - 108 dB.