1、CCIR VOLUME*III 90 m 4855232 0509477 2 m Rw. 338-2 RECOMMENDATION 338-2 7 BANDWIDTH REQUIRED AT THE OUTPUT OF A TELEGRAPH OR TELEPHONE RECEIVER - (Question 1/3, Study Programme 1A/3) (1953-1963- 1966- 1970) The CCIR, CONSIDERING (a) on adjacent channels, in the range 10 kHz to 30 MHz; (b) which dete
2、rmine the band of frequencies required for the overall system; the urgent need to determine the minimum separation between frequency assignments of stations operating that the width of the frequency band, which is necessary at the output of the receiver, is one of the factors (c) that, for telegraph
3、y, the. permissible degree of distortion is not yet defined; (d) in use, that, for telephony, the bandwidth m UNANIMOUSLY RECOMMENDS 1. that, for telegraphy, a provision for classes of emission A1A and AlB, the bandwidth in hertz, after the final detector stage, should be . 1.2 for class of emission
4、 FlB, the bandwidth in hertz after the discriminator, should be equal to 1.4 times the modulation rate in bauds. The extent to which these values can be applied, to permit closer spacing of adjacent channels, depends upon the degree and speed of amplitude variations due to fading and upon the differ
5、ential fading of the frequencies corresponding to the two significant conditions of modulation; 2. necessary, for each speech channel at the output of the receiver, should be as follows: that, for telephony, as a compromise between intelligibility and economy of bandwidth, the bandwidth 2.1 in accor
6、dance with Recommendation 335, the upper limit frequency should be reduced to 3000 Hz or less but no lower than 2600 Hz. In the case of the improved radio telephone system using a .linked compressor-expander (Recommendation 459, the bandwidth should be strictly preserved to not less than 3000 Hz; 2.
7、2 channels should be 100 Hz; the lower frequency limit of speech channels should be 250 Hz, and that of programme transmission 2.3 for systems employing commercial privacy equipment, the necessary bandwidth for satisfactory service may require the use of an upper limit frequency greater than 2600 Hz (e.g. in five-band privacy equipment the necessary bandwidth is 2750 Hz, the upper limit being 3000 Hz). COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services
