Abstract: For adaptively adjusting the gain in a modem receiver comprising two amplifiers (15, 19), the following steps are performed: for a buffer (21), a Hilbert filter (23), and an equalizer (27), a respective energy indicator (P.sub.max.sup.2, u.sub.avg.sup.2, x.sub.avg.sup.2) is generated from the signal samples in the respective delay line. Each energy indicator is compared to an associataed upper target level (4L.sub.U, 3L.sub.P, 1.19 L.sub.X), and for the equalizer also to an associated lower target level (0.84 L.sub.X). If necessary, a gain correction factor (S) initially set to 1.0 is modified to obtain an overall gain that keeps delay line energies within desired targets. Target comparisons are made so that excess energy in the buffer or Hilbert filter result in a rapid gain reduction whereas average equilizer energy is used for slow adaptations. After a gain change, all acquired samples in the delay lines are also multiplied by the correction factor (S) so that none is lost during gain acquisition.

Abstract: For rapidly detecting a periodic training signal in a modem receiver, delay line storage (21) is provided for a signal section which is equal to one training signal period (q.multidot.M samples) plus an additional adjacent window (q.multidot.W samples). Thus, the stored signal section includes two windows (17', 19) which are offset by one training signal period and which are similar if a training signal is present. In evaluation means (41) connected to the two windows (17', 19), two auxiliary signals (z.sub.1, z.sub.2) are generated (61, 65) which represent the signal energy and the correlation, respectively, of the samples in the two windows. From the auxiliary signals, a dissimilarity metric (z.sub.3) is derived (69) and is compared (73) to a given threshold for generating an indicator signal (CYC) which becomes active when a training signal is present, i.e. when the two window contents are similar and the metric (z.sub.3) falls below the threshold. A carrier frequency offset estimate (.DELTA..sub.