1、CCIR RECMN8773 92 = 4855232 0539235 342 6 Rec. 773 RECOMMENDATION 773* RADIO-FREQUENCY PROTECTION RATIOS REQUIRl3D BY FM SOUND BROADCASTING IN THE BAND BETWEEN 87.5 MHz AND 108 MHz AGAINST INTERFERENCE FROM D/SECAM TELEVISION TRANSMISSIONS (Question 72/10) (1992) The CCIR, considering that in some a
2、reas of Europe the part below 100 MHz of the VHF band II is used for television broadcasting: that for planning of sound broadcasting in that band it is, therefore, necessary to know to what extent the a) b) reception of sound broadcasting signals is interfered with by television transmissions, reco
3、mmends that the criteria contained in Annex 1 should be used to protect the sound broadcasting service against interference from D/SECAM television transmissions. ANNEX 1 1. Introduction Measurements have been made in the Federal Republic of Germany and Finland, to study the radio- frequency protect
4、ion ratios required by sound broadcasting reception against interference from D/SECAM television transmissions. 1.1 Measuring conditions 1.1.1 Measurements carried out in Finland In Finhnd, five representative domestic sound broadcasting receivers were measured making use of a D/SECAM television sig
5、nal generator as the unwanted transmitter. The measurements were performed in accordance with Recommendations 468 and 641. The D/SECAM television signal generator used was modulated by a 13 x 17 grid electronic test pattern signal with 90% modulation depth. The sound carrier was at a level of -10 dB
6、 with respect to the vision carrier and was modulated by a 1 O00 Hz signal with + 50 kHz deviation. The wanted reference system was 1 O00 Hz with +75 kHz deviation. The input level was 66 dB(l FV) into 75 Cl. The signal-to-noise ratio required was 50 dB measured according to Recommendzition 468. In
7、the range of wanted signal frequencies from 0.5 MHz to 4 MHz above the visioncarrier, the required protection ratio values were found to be greatly dependent on picture content. The worst interference with varying degrees of frequency dependence was produced by test patterns. In this range, therefor
8、e, an envelope curve has been taken to represent the interference potential of commonly-used test pictures. 1.1.2 Measurements carried out in the Federal Republic of Germany In the Federal Republic of Germany the RF wanted-to-interfering signal ratios were measured using one re-broadcast receiver an
9、d one domestic sound broadcast receiver of medium quality which reasonably met the RF protection ratio curves of Recommendation 412. * This Recommendation should be brought to the attention of Study Group 11. CCIR RECMN*773 92 m 4855252 0519236 289 m Rec. 773 7 The measurements were made using a PAL
10、 transmitter but with a vision-sound-carrier spacing of 6.5 MHz. The vision-to-sound-carrier ratio was chosen as 10 dB. Taking account of the greater video bandwidth of the D/SECAM standard the interference in the frequency range between 5 MHz and 6 MHz was extrapolated from the results at lower fre
11、quencies. The frequency of the chrominance sub-carrier was at approximately 4.433 MHz according to the PAL standard but when evaluating the results, the special conditions of the D/SECAM standard using two sub-carriers at frequencies 4.25 MHz and 4.4 MHz were taken into account. The measurements wer
12、e made according to Recommendation 641 using the D/SECAM television signals as the interfering signai. However, the interfering sound carrier was only modulated with a quasi-peak deviation of f24 Hz, thereby taking account of the smaller maximum deviation of f50 kHz for the sound in television syste
13、ms. For the video signal, different test patterns were used. 1.1.3 Comparison of the resuls The results obtained from the measurements carried out in the Federal Republic of Germany generally confirm those carried out in Finland. As a result of the different measuring methods and equipment used, the
14、 radio-frequency protection ratios differ below -1 MHz relative to the vision carrier and around the colour sub-carrier frequencies above 4 MHz. The results obtained in the Federal Republic of Germany require lower protection ratios below -1 MHz for stereophonic reception and above 4 MHz for monopho
15、nic reception. 2. Radio-frequency protection ratios Based on the measurements described in Q 1 the following radio-frequency protection ratios required by the sound broadcasting service against interference from D/SECAM television transmissions are given in Fig. 1 and Table 1. FIGURE 1 Radio-frequen
16、cy protection ratio required by frequency modulation sound-broadcasting at frequencies between 87.5 and 108 MHz against interference from D/SECAM television transmissions (Steady interference) 50 40 30 o 20 E .,o 10 3 $0 2 .- c1 d c1 O -10 -20 -30 -3 -2 -1 O 1 2 3 4 5 6 7 a 9 10 Frequency relative t
17、o vision carrier (MHz) : stereo : mono - - - - - CCIR RECMN8773 92 4855232 0519237 115 M Rec. 773 TABLE 1 Radio-frequency protection ratio required by frequency modulation sound broadcasting at frequencies between 87.5 and 108 MHz against interference from D/SECAM television transmissions (Steady in
18、terference) RF protection ratio (dB) Mono - 30 -2 O 19 24 30 35 30 24 19 10 O -I -3 -4 -5 8 10 10 8 -5 - 15 - 25 - 13 -5 6 15 25 28 25 15 6 -3 - 30 Stereo - 12 18 20 25 35 50 45 50 35 31 25 20 20 18 17 15 25 26 26 25 15 O -5 -6 5 26 40 43 35 43 40 26 O - 13 Note I - For tropospheric interfererice (p
19、rotection 99% of the time) these values may be reduced by 8 dB. Note 2 - Values for frequencies from 0.5 to 4 MHz are greatly affected by picture content. The figures given are for a test pattern and are representative of the on-the-air test picture transmissions. Nte 3 - The effect of offset frequency operation should be taken into account separately especially when using frequencies near the carrier frequency.
