| 摘要 |
In a device to improve the return loss or loop gain in intercom systems, in which at least one filter with a comb-filter-like structure but with pass bands and stop bands offset against one another in each case forms a chain circuit, thereby increasing the overall loop loss, it is proposed to arrange the pass bands and stop bands of the filters in a non-harmonic relationship, to implement increasing stop band attenuation with increasing frequency and furthermore to design the respective pass bands and stop bands of the bandpass filters significantly below 1/2 third octave. Finally, the spectral components which lie in a stop band can also be shifted into the nearest adjacent pass bands and added to the spectral components which have been allowed to pass through. Each telephone station preferably has two filters with different structures so that the speech paths in each case have a given, albeit different, transmission function, whereas the transmission function for the acoustic and electric return loss is virtually zero.
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