1、STD-CEPT ERC REPORT 22-ENGL 1993 II 232b414 0025170 13 a3 ERC REPORT 22 ., .-.- ._ - “- . ._.- % 7 European Radiocommunications Committee (ERC) “ within the European Conference of Postai and Telecommunications Administrations (CEPT) ERMES / TV E-5 COMPATIBILITY Montreux, October 1993 STD-CEPT ERC RE
2、PORT 22-ENGL 1993 I 232b414 0015171 75T I Copyright 1994 the European Conference of Postal and Telecommunications Administrations (CER) STD-CEPT ERC REPORT 22-ENGL 3993 1 2326434 0035372 by6 1 ERC REFORT 22 Page 1 ERMES / 177 E-5 COMPATIBILITY 1. EXECUTIVE SUMMARY 1.1 The results of theoretical, lab
3、oratory and field studies have been considered during this exercise in order to assess the mechanisms that can lead to ERMES transmitters affecting VHF Television channel E5 services within Europe, and assess the magnitude of the problem. 1.2 Findings indicate that a signifiant problem exists and th
4、at dependant upon the severity of the impairment, solutions may have to be selected on a case by case basis as necessary. 1.3 Viable options identified by the committee for alleviating the problem are as follows in no particular order: The use of ERMES channels that are within 25 Wz of a channel E5
5、sound image frequencies should be avoided where possible, refer to Table 7; The power of the ERMES signal in areas where TV channel E-5 is in common use should be minimised where possible; Orthogonal polarisations should be used where possible (both polarisations are used for TV broad- casting in ma
6、ny countries); Care should be exercised in the siting of ERMES transmitters; The installation of in-line filters in the receiving system where necessary; Interference car be minimised by shifting the frequency offset of the TV transmitter (in multiples of line frequency); ERMES and TV operators need
7、 to take account of the potential problems in planning their networks; Further field trials should be undertaken to quantify the magnitude of the problem. 2. INTRODUCTION 2.1 ERMES stands for European Radio Message System intended for pan-European use. The ERMES specification (pr ETS 300 133-4) prov
8、ides for sixteen channels with centre frequencies defmed by fn=169.400 + n*0.025 MHz, where n = channel number = 1 to 16. 2.2 The actual use of the ERMES channels in each CEPT country will be a national matter, taking into account the need for frequency coordination between countries and CER Rec. TI
9、R 25-07. 2.3 Affected television systems currently in use in member states include both B-PAZ, and L-SECAM, see CCIR report 624-4. 2.4 Tests in several CER countries have shown that interferences are likely to occur from ERMES to TV channel E.5. The purpose of this report is to evaluate the results
10、of these tests and propose feasible solutions to identified problems. STD-CEPT ERC REPORT 22-ENGL 3993 I 232bYL4 00115373 522 ERC REPORT 22 Page 2 2.5 3. 3.1 3.1.1 3.1.2 3.1.3 3.1.4 3.2 During the introduction of the Swedish POCSAG system operating on ERMES channel 16, several problems were experien
11、ced. Around 500 cases of interference to TV channel E5 were reported. The problems were usually solved by installing filters at the receiving location, however in some serious cases the POCSAG transmitter had to be moved away from the main lobe of the TV antennas. THEORETICAL STUDY Interference Mech
12、anisms The various carriers used in TV channel E5 in Europe have nominal frequencies as follows: Vision carrier, fv: 175.25 MHz (176.0 MHz in France) Sound carrier, fs: 180.75 MHz (182.5 MHz in France) Second sound carrier, fs2: 180.992 MHz The second sound carrier is used in the following countries
13、: Austria, Germany, Italy, the Netherlands and Switzerland. NICAM carrier, fN: 181.10 MHz, constant bandwidth: 520 IrHZ NICAh4 on channel E5 is used in the following countries: Denmark, Finland, Iceland, Norway, Spain and Sweden. The ERMES carriers are: fE= 169.4 MHz + 25nWz, n = 1 to 16 i.e. Channe
14、l 1 = 169.425 MHz and Channel 16 = 169.800 MHz The frequency difference between the vision carrier and the ERMES carriers is between 5.45 and 5.825 MHz (6.2 MHz and 6.575 MHz in France). According to CCLR recommendation 851, a protection ratio of -10 dB is required for a continuous CW interferer 6 M
15、Hz below the vision carrier. ERMES can cause interference to the TV sound in two different ways: i either because some ERMES channels will occur as image frequencies of the sound carrier with respect to the vision carrier in the IF stage of the TV receiver, this will be the dominant interference mec
16、hanism in receivers with poor IF selectivity; ii) or through the intermodulation product 2f,fe, since this product falls in the range 180.7 - 181.075 MHz (182.2 - 182.575 MHz in France). In both cases, it is the same group of ERMES channels that would cause the most interference. ERMES channel 14 (c
17、hannel 4 in France) causes interference to fs; ERMES channels around 4 causes interference to fs2; Adjacent ERMES channels are also likely to affect the sound; ERMES channels 1 through 10 cause interference to the NICAM channel. Calculation of Interference Distances STD-CEPT ERC REPORT 22-ENGL 1773
18、232b414 OOL5L74 4b9 E 3.2.1 3.2.2 3.2.3 3.2.4 3.3 3.3.1 3.4 3.4.1 3.4.2 ERC REPORT 22 Page 3 The interference distances calculated below are based on the protection ratios obtained in one set of laboratory tests. With an EFW of 100 W the field strength at the distance d(m) in free space can be calcu
19、lated as: E(dBpV/m) = 2O1og(7*1O7 Id). Assuming O dBd antenna gain and an input resistance of 754 the conversion factor from field strength to input terminal voltage in the TV receiver is -1 1 dB. According to CCIR report 625-4, the antenna gain in band Dl can be taken as 7.5 dBd, and the cable loss
20、es are 1.5 dB. When the TV and ERMES transmitters are located in the same direction from the receiver, the separation distances are then as given in Table 1, column 3. Angle separation between the TV and ERMES transmitting antennas will give a considerable improvement. According to CCIR recommendati
21、on 419-2, band III TV receiving antennas give 12 dB antenna discrimination for angle separations greater than 60, see Table 1, column 4. The distances shown in Table 1 are valid when the ERMES and TV transmissions have the same polarisation. If orthogonal polarisation is used polarisation discrimina
22、tion will help to protect the TV service and thus reduce the necessary separation distances. According to CCIR Rec. 419-3 a polarisation discrimination of 18 dB is considered typical in Band III. In the same recommendation it is also stated, that polarisation discrimination varies statistically with
23、 locations and that a value of 10 dB will be exceeded at 90% of locations. As the distances in question are short, interference bom ERMES transmissions into TV must be assumed continuous, hence the polarisation discrimination value of 10 dB has been used in the calculations. The results of which are
24、 listed in Table 2. It shall be noted, that according to CCIR Rec. 419-3 polarisation discrimination can only be used inside the sector defined by the ?Beam width? of the receiving antenna, i.e. f 60 for a Band Dl antenna. Outside of this sector the values given in Table 1, column 4 shall be used. S
25、ignal Level and Field Strength The tests on television receivers, the results of which were used to calculate interference distances, were made with wanted receiver input signal levels of 80, 70 and 60 dBpV respectively. Based on the values given in CCIR Report 625-4 for cable loss, antenna conversi
26、on factor and antenna gain, these input levels correspond to field strength values of 85 dBpV/m, 75 dBpV/m and 65 dBpV/m. Fringe Area Situation According to CCIR Rec. 417-4 the lowest field strength for which protection can be claimed is 55 dBpV/m in Band IiI. Coverage is actually achieved with this
27、 value in some European countries. Assuming that the protection ratios measured for a wanted input signal level of 60 dBpV are also valid for 50 dB pV (field strength = 55 dBpV/m), the separation distances will be as listed in Table 3. in the Tables 1 to 3 the interfering ERMES field strength has be
28、en calculated by the formula valid for free space propagation. This formula cannot be used for terrestrial distances greater than a few kilometres, depending on the effective antenna height. Page 4 4. 4.1 4.1.1 4.1.2 4.1.3 4.2 4.2.1 4.2.2 4.2.3 The distances given in Table 3 have therefore been reca
29、lculated using the formula for free space propagation for distances up to 5 kilometres and the CCIR Rec. 370-5 VHF 50%, 50%, land curves extrapolated down to 5 km for distances above 5 km. The results are listed in Table 4 for an ERMES antenna height of 75 metres, and in Table 5 for an ERMES antenna
30、 height of 300 metres. LABORATORY AND FIELD STUDIES Influence of the Television Receiver Design As stated in section 3 of this paper, there are two ways by which the interference to the sound occurs: by intermodulation and by breakthrough at the sound image frequencies. Which phenomenon is the most
31、important depends on the input signal level and the receiver design. Important is the selectivity of the receiver at the ERMES frequencies, when tuned to channel E-5. Since the ERMES frequencies are relatively close to the received frequency, not much selectivity is provided by the channel selector.
32、 The main selectivity is within the IP part of the receiver. This selectivity can only improve the breakthrough behaviour, which is dominant at input signal levels which are not too high. The IF selectivity depends on the concept of the receiver front-end. Three main concepts are used. i) Receivers
33、for FM mono sound, in most cases, make use of the inter-carrier principle; ii) Receivers for stereo sound (NICAM or analogue FM), in most cases, make use of the Quasi Split Sound (QSS) principle; iii) Receivers for the L-SECAM standard (AM sound) make use of the Split Sound (SS) principle. In the QS
34、S and SS receiver a separate filter is used for the sound channel and this provides greater selectivity and rejection at the ERMES frequencies, reducing the disturbance in the sound channel. It can be said that receivers in the lower price range are built according to the inter-carrier principle. Th
35、e difference in the performance in the presence of ERMES interfering frequencies can be up to 20 dB. Measurement Results Laboratory measurements on a limited sample of typical television receivers have been conducted in a number of CEPT countries. In this report the results of these measurements hav
36、e been summarised in terms of protection ratios (Ca) in ii) for receivers with analogue sound, ERMES channels 4, 5 and 14 (and in some cases 13 and 15) are the most critical; iii) for L-SECAM (AM sound) receivers, measurements are currently being conducted in France. These measurements could confirm
37、 that ERMES channels 3,4 and 5 are the most critical. STD-CEPT ERC REPORT 22-ENGL L993 I 2326434 0015176 23L 111 ERC REPORT 22 Page 5 4.3 Field Measurement Results 4.3.1 The preliminary results of field trials conducted in Germany showed more optimistic results than those from the theoretical work a
38、nd laboratory measurements contained in this report. 5. OBSERVATIONS 5.1 The use of existing TV receivers and channel 5 are unavoidable. 5.2 Not aii countries use the same frequencies for the sound sub-carriers, and therefore the ERMES channels to be avoided may be different for neighbouring countri
39、es. 5.3 The use of the ERMES channels adjacent to that which falls directly on the image of the TV sound sub-carriers could also result in interference. 5.4 The tests on a limited sample of TV receivers shows the that the receivers employing the inter-carrier system were considerably more susceptibl
40、e to sound interference than those employing the quasi-split sound system. 5.5 TV broadcasting uses frequency offsets to reduce Co-channel interference. The particular offset used could affect the magnitude of the interference from a particular ERMES channel. In order to improve the protection ratio
41、 between TV co-channel transmitters frequency offsets of the sound and vision carriers are determined during the planning phase. Frequency offsets in steps of 15625/12 Hz are implemented (U12 of the line frequency). Offset steps toward higher frequencies are designated with a P and toward lower freq
42、uencies with an M i.e. 4P, 8M. A maximum protection ratio between two transmitters is achieved with a frequency offset of 6 f n* 12 (where n is an integer) steps. If the interference between three or more transmitters is to be reduced, an offset of 4 or 8 -C n* 12 (where n is an integer) steps are c
43、onsidered to be desirable. Depending on the choice of frequency offsets the level of “tolerable interference“ between the TV transmitters using channel E-5 can be improved by as much as 19 dB. Any interference problems which arise with the introduction of ERMES are mainly due to ERMES channels 4 and
44、 14 (interference to analogue sound), and ERMES channels 1 to 10 (interference to NICAM). In view of the frequency offsets normally used by TV transmitters, interference problems may also be caused by ERMES channels 3, 5, 11, 13 and 15. 6. CONCLUSIONS 6.1 It is clear, both frompast experiences and t
45、est results, that there will be some cases of interference from ERMES transmitters to the reception of TV channel ES. The interference can affect both the sound and the picture. Interference distances can be expected to range from at least 100 metres up to several kilometres, depending on the receiv
46、ed signal level, the relative positions of the antennas, polarisation and local terrain. 6.2 Critical Frequencies In the case of picture disturbances, generally speaking, all ERMES channels have the same influence. For sound disturbances, the ERMES channels identified as being particularly problemat
47、ic are shown in table 7. ERC REPORT 22 Page 6 6.3 6.4 6.5 6.6 7. 7.1 7.2 7.3 Frequency Offsets used by TV Broadcasting Interference between ERMES and TV broadcasting on channel E-5 can be minimised by shifting the frequency offset of the TV transmitter. Such shifts must be in steps equal to the line
48、 frequency (15625 Hz) to maintain the mutuai protection between ccxhannel TV transmitters. When shifting three times the line frequency or less, no action has to be taken on the receiver side. When shifting more than three times the line frequency, cable head- ends might need readjustment. Choice of
49、 ERMES Transmitter Locations (based on existing TV transmitter locations) If the ERMES and TV transmitters can be co-located, all of the ERMES channels can be used. However, this assumes that the ERMES e.r.p. in all directions is lower than the TV transmitter e.r.p. by more than the required protection ratio (this difference can be less in the case of orthogonal polarisation). If this requirement can be met, the interference potential of a particular ERMES transmitter can be minimised by choosing the same, or near locations, for the ERMES transmitter as the TV broadcasting E5 t
