ITU-T R 78-1988 PILOT CHANNEL FOR AMVFT SYSTEMS《调幅音频电报系统的导频通路》.pdf

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1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 2 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%2!0(94%,%2!0(G0G042!.3-)33)/.0),/4G0G0#(!%,G0G0amended at New Delhi, 1960)The CCITT,considering(a) that use of a pilot channel is suggested to give an alarm in the case of an abnormal drop in the receivin

2、glevel of the bearer circuit in amplitude-modulated voice-frequency telegraph (AMVFT) systems;(b) that service channels could have been used as pilot channels for this alarm signal, but since there is notalways a service channel in each VF group, it is suggested that channels be chosen for the alarm

3、 signal,unanimously declares the view(1) that it is advisable to use a pilot channel to give an alarm in the case of an abnormal drop in the receivinglevel of the bearer circuit carrying an AMVFT system;(2) that the level at which the alarm should work should be fixed by the Administration at the re

4、ceiving end;(3) that the pilot channel frequency should, as far as possible, be 300 Hz, transmitted with a power levelcorresponding to that of a frequency-modulated channel in accordance with Table 1/R.35;(4) that, if such an arrangement cannot be adopted, the Administrations concerned should agree on the use ofone of the standardized frequencies for the pilot channel used for alarm purposes.Note The case of 50-baud frequency-modulated systems is dealt with Recommendation R.35.