1、- STDaBSI BS EN b0244-14-ENGL 1777 W Zb24bb9 Ob4738b 782 BRITISH STANDARD Methods of measurement for radio transmitters Part 14. External intermodulation products caused by two or more transmitters using the same or adjacent antennas The European Standard EN 60244-14 : 1997 has the status of a Briti
2、sh Standard ICs 33.060.20 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BS EN 60244-14 : 1997 1997 IEC 60244-14 - STD-BSI BS EN b0244-14-ENGL 1977 Lb24bb9 Ob47387 819 BS EN 60244-14 : 1997 National foreword This British Standard is the English language version of EN 60244-14
3、 : 1997. It is identicai with IEC 60244-14 : 1997. The UK participation in its preparation was entrusted to Technical Committee EPU103, lansmitjng equipment for radiocommunication, which has the responsibility to: - aid enquirers to understand the text; - present to the responsible intermtionavEurop
4、ean commime any enquiries on the interpretation, or proposals for change, and keep the UK inkrests informed; - monitor related international and European developments and promulgate them in the UK. A list of organizations represented on this committee can be obtained on request to its secretary. Fro
5、m 1 January 1997, all IEC publications have the number 60000 added to the old number. For instance, IEC 27-1 has been renumbered as IEC 60027-1. For a period of time during the change over from one numbering system to the other, publications may contain identifiers from both systems. Cross-reference
6、s Attention is drawn to the fact that CEN and CENELEC Standards nody include an annex which lists nonnative references to intemationai publications with their corresponding or European publications. The British Standards which implement these international or European publications may be found in th
7、e BSI Standards Catalogue under the section entitled international Standards Correspondence Index, or by using the Find facility of the BSI Standards Electronic Catalogue. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document com
8、prises a hnt cover, an inside front cover, the EN title page, pages 2 to 24, an inside back cover and a back cover. This British Standard, having been prepared under the direction of the Elecrotechnicai sedor Board, was published under the authority of the Standards Board and comes into effect on 15
9、 October 1997 O BSI 1997 ISBN O 680 28460 9 Amendments issued since publication AmdNo* ID - stop filter insertion loss (this is particularly important for any I? close to a carrier frequency) : - main transmitting feeder loss. NOTE - The measurement described in 4.2 does not represent the actual rad
10、iated level from the antenna. To obtain the radiated level, correct the results as described in 4.3 c), taking into account the frequency response andlor VSWR of the antenna. STD-BSI BS EN bU244-14-ENGL 1777 D Lb24bb9 Ob47395 995 Page 8 EN 60244-14 : 1997 4.4 fl-air measurements a) Connect the test
11、equipment to a calibrated broad-band receiving antenna at the location where the measurements are to be made, as shown in figure 2. b) Carry out the tests described in 4.2 b), 4.2 c), and 4.2 d). c) When making measurements, take into account the precautions listed in 4.3 a) and 4.3 b) and correct t
12、he results as described in 4.3 c), where applicable. In addition, also correct the results to allow for differences in receiving antenna gain at the carrier frequencies and IP frequencies. 4.5 Special precautions to be observed when making off-air measurements The signal levels received can be criti
13、cally dependent upon the location of the receiving antenna. The measuring site should be sufficiently distant and on an appropriate bearing to ensure that the receiving antenna lies within the main horizontal and vertical radiation lobes of the transmitting antenna. Where directional arrays are invo
14、lved, the radiation patterns may differ considerably if the frequency spacing between carrier and the intermodulation product frequencies is Significant. In all such cases, off-air measurements are not generally relevant, except in those cases where intermodulation product levels are of particular i
15、nterest, in a specific direction or location, e.g. where interference to aeronautical services is possible. This effect is particularly significant for VHF installations using parallel transmitters (Le., two completely independent transmission chains per service, where each transmitter of a parallel
16、 pair feeds a separate half antenna). With this configuration of transmission system, when intermodulation products are generated due to imperfect isolation of the antennas, the phase of the interfering signal will be random and, therefore, the phase of the intermodulation products generated in the
17、two halves will not bear any fixed relationship to the phase of the carrier. As a result, the radiation pattern of the antenna is likely to be different for the carrier frequency and each intermodulation product. It is important to check that off-air measurements have not been corrupted by local ref
18、lections or multipath effects, etc. The measurements should therefore be repeated with the receiving antenna repositioned at a number of nearby points to check for consistency of results. Locations where significant variations in the relative levels of the carrier and IP components are observed shal
19、l be avoided. 5 Methods of measurement for specific transmitter service or configuration 5.1 Measurements for VHF radio transmitters In order to make measurements on VHF broadcasting transmitters operating in accordance with ITU-R Recommendation 329-6, the following equipment requirements (see figur
20、es 1 and 2) apply: - spectrum analyzer: bandwidth 3 kHz to 1 MHz, dynamic range at least 70 dB, for example; - directional coupler: 20 dB to 30 dB directivity, for example; - stop filters (one for each transmission): attenuation at unwanted frequency approximately 55 dB, insertion loss approximately
21、 2 d6, for example; STD-BSI BS EN b244-14-ENGL 1777 1b24bb7 b4737b 21 Page 9 EN 60244-14 : 1997 - tuneable bandpass filter: i100 kHz at 3 dB points (for off-air measurements), for example; - wide band, low noise amplifier: 20 dB gain (for off-air measurements), for example. 5.2 Measurements for adja
22、cent antennas Figure 3 shows a general arrangement for transmitters feeding separate antennas e.g. for LF, MF and HF multiple transmitter installations, or stations for television and FM sound broadcasting. The directional coupler output voltages are measured by means of a spectrum analyzer, indicat
23、ing the amplitudes of all interference products on a single trace (see figure 1). Alternatively, a selective test receiver may be used. The latter will in many cases be convenient, although the spectrum analyzer has the advantage of showing all signals simultaneously, making it relatively easy to se
24、lect the frequencies of interest. The powers are calculated by means of the formulae (A.4-1) and (A.4-2), based on the voltages measured. The frequency dependency of the coupling coefficients shall be allowed for, requiring additional corrections. With this set-up, all external interference products
25、 of interest can be measured. 5.3 Measurements for a common antenna 5.3.1 Method 1 Figure 4 shows a layout of a transmitter site in which two or more transmitters are coupled to a common antenna via a combining unit. In this case, the intermodulation products are measured at the common directional c
26、oupler (DC) using the set-up in figure 1 or 2, and the levels are calculated from the formulae (A.4-1) and (A.4-2). In this arrangement, the external second-order intermodulation components, .e. for which p = q = 1, cannot be measured exactly because the second-order interference products from each
27、transmitter coincide in frequency. Furthermore, because of different and, in some cases, variable phase relationships, due to modulation processes for example, the resultant amplitudes may vary considerably. On the other hand, in this configuration, the second order (p = Q = 1, o = 2) external inter
28、ference products will be greatly reduced because the two transmitters are decoupled by selective networks. This is, however, not always the case for installations with close coupled antennas (see figure 3). 5.3.2 Method 2 If the second-order products are relatively high for transmitters sharing a co
29、mmon antenna, a second method shown in figure 5 may be used. Directional couplers at the outputs of the transmitters, .e. in front of the combining devices, are needed as in the case of an installation conforming to figure 3. STD-BSI BS EN 60244-14-ENGL 1997 = 1624669 0647397 7b8 Page 10 EN 60244-14
30、 : 1997 The attenuation of the combining unit from transmitter input to antenna at each IP frequency should be measured beforehand so that the levels measured at the transmitter output can be corrected. This method can be used when an insufficient number of stop filters is available to carry out the
31、 measurements described in the first method between the combining equipment and antenna. Again, if an antenna matching unit (AMU) is used, no directional coupler will be available in front of the antenna. In this case, the directional couplers at the outputs of each transmitter shall be used, thereb
32、y enabling ali orders of radiated interfering signals to be measured. 5.3.3 Method 3 In the case of a transmitter site where several transmitters operating at different frequencies are combined into groups, each group may be treated as a single transmitter (except of course, for the intermodulation
33、products, which are a function of the total number of transmitters at the site). An adjacent (combined) transmitter group may absorb RF energy from the transmitter group under test, as in the case of a single transmitter. Accordingly, the common directional coupler (DC) is also used to determine the
34、 absorbed energy, measuring the voltages VIF and U, indicated in parentheses (in figure 4) and using the formulae (A.4-1) and (A.4-2). The total number of intermodulation products emitted at the transmitter site may be calculated from the formula (A.3-1) where x is still the total number of transmit
35、ters in operation, independent of the number of groups. Because of second-order interference within each group of transmitters, a combination of the methods 2 and 3 described in 5.3.2 and 5.3.3 may be used to determine the values necessary to calculate all external intermodulation products levels. 6
36、 Presentation of the results The results shall be expressed either in decibels relative to the level of the carrier frequency (f,) and order of intermodulation products (o) at specified frequencies, or in dBm or in absolute value mV. The results may be tabulated or plotted on a graph as a function o
37、f carrier frequency (fm) and order of intermodulation products (o), or may be presented as a photograph or as a hard copy of the spectrum analyzer display when a sweep method of measurement is used. However, in the case of the latter, compensation needs to be applied to the attenuation factors, whic
38、h are dependent upon the frequency. Furthermore, the forward as well as the reflected values must be measured and the net radiated value calculated. The display indication is only correct in the forward case when the antenna is matched to the intermodulation product frequencies. This will only apply
39、 in some certain cases. Therefore, photographs of the displays alone will generally not be sufficient to represent correct results. In general, a tabulation of the results will be more appropriate because additional calculations and corrections will always be needed (see 4.3) and 4.4 c). For this pu
40、rpose, the form contained in annex B is recommended. STD-BSI BS EN b0244-14-ENGL 1997 m lb24hh9 b47398 bT4 stop Tunable Pre- - Wideband - Spectrum filters selector amplifier analyzer T1 I I Directional coupler COM- BI- I? NER 1 U Page 11 EN 60244-14 : 1997 Figure la - Single antenna T1 Directional c
41、oupler T2 qr e stop Spectrum filters . iEC 49597 Figure 1 b - Separate antennae Figure 1 - Measurements in transmitter feeders STD.BSI BS EN b024Li-14-ENGL 1997 LbELibbS Ob47399 530 LL n- U n- Page 12 EN 60244-14 : 1997 U c5- u, 3- w n n- t -I- STDSBSI BS EN b0244-14-ENGL 1777 D Lb2Libb7 Ub47400 O82
42、 Page 13 EN 60244-14 : 1997 I Y IL LL 3- 3- Y * rn * I P STD.BS1 BS EN h0244-L4-ENGL 1997 Lh24bb9 Ob4740L TL9 = Page 14 EN 60244-14 : 1997 n a n n- - W I- I n s4 Y n LL LL LL 3- 3- U Y E W L u. U - LL I nE nk U n- t U If, LL 5- m E o “1 LI E U 5- Y 0 c STD-BSI BS EN b0244-14-ENGL 1777 1b24bb7 b47402
43、 755 Coaxial switch matrix - Transmitters Page 15 EN 60244-14 : 1997 Antenna Balun (1 cl IEC 501Y97 Modem transmitter Figure 6a - Modern station Balun - , n LL . I Old 1 I transmitter I -I - Balanced switch matrix Antenna 1 IEC 501/97 IIIII Figure 6b - Older statlon with some transmitters with open
44、transmission lines Figure 6 - Typical HF station configurations STD-BSI BS EN b0244-14-ENGL 1997 M 1b24bb9 b47403 91 M Page 16 EN 60244-14 : 1997 Annex A (normative) Theoretical notes A.1 Nomenclature The following symbols are used throughout this standard. index number of transmitter transmitter nu
45、mber m operating frequency of Tx, directional coupler associated with Tx, intermodulation product frequency forward carrier signal level, measured at the directional coupler OC, order of harmonic for f, (max. 3) order of harmonic for f, (normally 1, .e. fundamental) reflected intermodulation signal
46、level, measured at the directional coupler 0% forward intermodulation signal level, caused by transmitter Tx, (towards transmitter Tx,), measured at the directional coupler OC, reflected intermodulation signal level, caused by transmitter Tx, (from transmitter Tx,), measured at the directional coupl
47、er OC, forward intermodulation signal level, measured at the directional coupler OC, coupling factor of directional coupler OC, (relative value) (dB), sometimes a function of the operating frequency f number of permutations of interference intermodulation products per site order of external intermod
48、ulation product (o = p + 9) nominal output power of x, forward intermodulation product power, originating from x, reflected intermodulation product power, reflected towards x, STD-BSI BS EN b0244-14-ENGL 1997 = Lb24bb7 Ob47404 728 * in * Page i7 EN 60244-14 : 1997 difference between PIF and Pl, forw
49、ard intermodulation product power, caused by transmitter Tx, and flowing towards Tx, reflected intermodulation product power, caused by transmitter Tx, and reflected from Tx, difference between Pl, and Pl, (for transmitter Tx,) emitted intermodulation product power PiD without compensation for feeder losses Pl, with compensation for feeder losses forward output power of Tx, ratio of the emitted intermodulation product power to the transmitter nominal power feeder impedance number of operating transmitters at the site A.2 Intermodulation product
