3.3. Table of maximum permitted spurious emission power levels
The following sections indicate the maximum permitted levels of spurious emissions, in terms of power as indicated in the tables, of any spurious component supplied by a transmitter to the antenna transmission line. Section 3.3.1 is applicable until 1 January 2012 to transmitters installed on or before 1 January 2003; Section 3.3.2 is applicable to transmitters installed after 1 January 2003 and to all transmitters after 1 January 2012. The frequency assigned to a station of a given service shall be separated from the limits of the band allocated to this service in such a way that, taking account of the frequency band assigned to a station, no harmful interference is caused to services to which frequency bands immediately adjoining are allocated. Spurious emission from any part of the installation, other than the antenna and its transmission line, shall not have an effect greater than would occur if this antenna system were supplied with the maximum permitted power at that spurious emission frequency. These levels shall not, however, apply to emergency position-indicating radiobeacon (EPIRB) stations, emergency locator transmitters, ships’ emergency transmitters, lifeboat transmitters, survival craft stations or maritime transmitters when used in emergency situations.
For technical or operational reasons, more stringent levels than those specified may be applied to protect specific services in certain frequency bands. The levels applied to protect these services, such as safety and passive services, shall be those agreed upon by the appropriate world radiocommunication conference. Additionally, special consideration of transmitter spurious emissions may be required for the protection of safety services, radio astronomy and space services using passive sensors. Information on the levels of interference detrimental to radio astronomy, Earth exploration satellites and meteorological passive sensing is given in the most recent version of Recommendation ITU-R SM.329. Spurious emission limits for combined radiocommunication and information technology equipment are those for the radiocommunication transmitters.
3.3.1. Spurious emission limits for transmitters installed on
or before 1 January 2003 (valid until 1 January
2012)
Radar systems are exempt from spurious emission limits under this Section. The lowest practicable power of spurious emission should be achieved.
Application of these limits
The frequency range of the measurement of spurious emissions is from 9 kHz to 110 GHz or the second harmonic if higher. Guidance regarding the methods of measuring spurious emissions is given in the most recent version of Recommendation ITU-R SM.329. The e.i.r.p. method specified in that Recommendation should be used when it is not possible to accurately measure the power supplied to the antenna transmission line (for example, radars), or for specific applications where the antenna is designed to provide significant attenuation at the spurious frequencies. Additionally, the e.i.r.p. method may need some modification for special cases, e.g. beam forming radars. Guidance regarding the methods of measuring spurious emissions from radar systems is given in the most recent version of Recommendation ITU-R M.1177. The reference bandwidths required for proper measurement of radar spurious emissions should be calculated for each particular radar system. Thus, for the three general types of radar pulse modulation utilized for radionavigation, radiolocation, acquisition, tracking and other radiodetermination functions, the reference bandwidth values should be:
– for fixed-frequency, non-pulse-coded radar, one divided by the radar pulse length, in seconds (e.g. if the radar pulse length is 1 ms, then the reference bandwidth is 1/1 ms = 1 MHz);
– for fixed-frequency, phase coded pulsed radar, one divided by the phase chip length, in seconds (e.g. if the phase coded chip is 2 ms long, then the reference bandwidth is 1/2 ms = 500 kHz);
– for frequency modulated (FM) or chirped radar, the square root of the quantity obtained by dividing the radar bandwidth in MHz by the pulse length, in seconds (e.g. if the FM is from 1 250 MHz to 1 280 MHz or 30 MHz during the pulse of 10 ms, then the reference bandwidth is (30 MHz/10 ms)1/2 = 1.73 MHz).
For those radar systems for which acceptable methods of measurement do not exist, the lowest practicable power of spurious emission should be achieved.
The spurious emission levels are specified in the following reference bandwidths:
– 1 kHz between 9 kHz and 150 kHz
– 10 kHz between 150 kHz and 30 MHz
– 100 kHz between 30 MHz and 1 GHz
– 1 MHz above 1 GHz.
As a special case, the reference bandwidth of all space service spurious emissions should be 4 kHz.
For the purpose of setting limits, all emissions, including harmonic emissions, intermodulation products, frequency conversion products and parasitic emissions, which fall at frequencies separated from the centre frequency of the emission by ± 250%, or more, of the necessary bandwidth of the emission will generally be considered as spurious emissions. However, this frequency separation may be dependent on the type of modulation used, the maximum bit rate in the case of digital modulation, the type of transmitter and frequency coordination factors. For example, in the case of digital (including digital broadcasting) modulation systems, broadband systems, pulsed modulation systems and narrow-band high power transmitters, the frequency separation may need to differ from the ± 250% factor. For multichannel or multicarrier transmitters/transponders, where several carriers may be transmitted simultaneously from a final output amplifier or an active antenna, the centre frequency of the emission is taken to be the centre of the – 3 dB bandwidth of the transmitter or transponder and the necessary bandwidth is taken to be the transmitter or transponder bandwidth. As the bandwidth of an emitted signal becomes more and more narrow (to the limiting case of an unmodulated carrier with a theoretical necessary bandwidth of zero), the application of the term “necessary bandwidth” as used in determining the region where spurious emission limits apply to space services becomes more and more difficult. In the limiting case, ± 250% of necessary bandwidth (recognized in many cases as establishing the region beyond which spurious emissions are defined) approaches zero. Radio beacon signals and other unmodulated signals, such as those used in uplink and downlink circuits in control and tracking of satellites, are examples of a case where it is difficult in practice to apply the concept of “necessary bandwidth” in determining where out-of-band emissions end, and spurious emissions begin. Pending further studies and definitive action by a future world radiocommunication conference for determining the portion of spectrum where spurious emission limits apply for transmitters using amplifiers to pass an essentially unmodulated signal (or a signal with very small bandwidth), the amplifier bandwidth is taken to be the necessary bandwidth.
For the case of a single satellite operating with more than one transponder in the same service area, and when considering the limits for spurious emissions as indicated in above, spurious emissions from one transponder may fall on a frequency at which a second, companion transponder is transmitting. In these situations, the level of spurious emissions from the first transponder is well exceeded by the fundamental or out-of-band emissions of the second transponder. Therefore, the limits of this Appendix should not apply to those spurious emissions of a satellite that fall within either the necessary bandwidth or the out-of-band region of another transponder on the same satellite, in the same service area (see Fig. 3.1).
Figure 3.1. Example of the applicability of spurious emission limits
Examples of applying 43 + 10 log (P) to calculate attenuation requirements
Where specified in relation to mean power, spurious emissions are to be at least x dB below the total mean power P, i.e. – x dBc. The power P (W) is to be measured in a bandwidth wide enough to include the total mean power. The spurious emissions are to be measured in the reference bandwidths given in the Recommendation. The measurement of the spurious emission power is independent of the value of necessary bandwidth. Because the absolute emission power limit, derived from 43 + 10 log (P), can become too stringent for high-power transmitters, alternative relative powers are also provided in Table 3.8.
Example 1
A land mobile transmitter, with any value of necessary bandwidth, must meet a spurious emission attenuation of 43 + 10 log (P), or 70 dBc, whichever is less stringent. To measure spurious emissions in the frequency range between 30 MHz and 1 GHz, Recommendation ITU‑R SM.329-7 recommends 4.1 indicates the use of a reference bandwidth of 100 kHz. For other frequency ranges, the measurement must use the appropriate reference bandwidths given in recommends 4.1.
With a measured total mean power of 10 W:
– Attenuation relative to total mean power = 43 + 10 log (10) = 53 dBc.
– The 53 dBc value is less stringent than the 70 dBc, so the 53 dBc value is used.
– Therefore: Spurious emissions must not exceed 53 dBc in a 100 kHz bandwidth, or converting to an absolute level, spurious emissions must not exceed 10 dBW – 53 dBc = _ 43 dBW in a 100 kHz reference bandwidth.
With a measured total mean power of 1 000 W:
– Attenuation relative to total mean power = 43 + 10 log (1 000) = 73 dBc.
– The 73 dBc value is more stringent than the 70 dBc limit, so the 70 dBc value is used.
– Therefore: Spurious emissions must not exceed 70 dBc in a 100 kHz bandwidth, or converting to an absolute level, spurious emissions must not exceed 30 dBW – 70 dBc = _ 40 dBW in a 100 kHz reference bandwidth.
Example 2
A space service transmitter with any value of necessary bandwidth must meet a spurious emission attenuation of 43 + 10 log (P), or 60 dBc, whichever is less stringent. To measure spurious emissions at any frequency, Note 10 to Table 3.8 indicates using a reference bandwidth of 4 kHz.
With a measured total mean power of 20 W:
– Attenuation relative to total mean power = 43 + 10 log (20) = 56 dBc.
– The 56 dBc value is less stringent than the 60 dBc limit, so the 56 dBc value is used.
– Therefore: Spurious emissions must not exceed 56 dBc in a 4 kHz reference bandwidth, or converting to an absolute level, spurious emissions must not exceed 13 dBW – 56 dBc = _ 43 dBW in a 4 kHz reference bandwidth.