RECOMMENDATION ITU-R SM.1539-1

Variation of the boundary between the out-of-band and spurious domains\
required for the application of Recommendations ITU-R SM.1541\
and ITU‑R SM.329

(Question ITU-R 211/1)

(2001-2002)

The ITU Radiocommunication Assembly,

considering

a\) that Recommendations ITU-R SM.1541 and ITU-R SM.329 give the
definitions of the terms "out-of-band domain" and "spurious domain", but
that these definitions do not precisely specify the boundary between the
out-of-band (OoB) and spurious domains;

b\) that the boundary between the OoB and spurious domains is important
for the application of both Recommendations ITU-R SM.1541 and ITU-R
SM.329;

c\) that the boundary between the OoB and spurious domains is, in
general, a function of the necessary bandwidth, but may be functions of
different parameters other than the necessary bandwidth in certain
applications;

d\) that the boundary between the OoB and spurious domains may require
variations, in particular, for narrow-band and wideband transmissions,
as well as for primary radars,

noting

a\) that, according to Recommendations ITU-R SM.1541 and ITU-R SM.329,
normally the boundary between the OoB and spurious domains is the
frequency separated from the centre frequency of the emission by 250% of
the necessary bandwidth of the emission (see Note 1),

recommends

**1** that Annex 1 should be referred to in the case of variation of the
boundary between the OoB and spurious domains which may be required for
the application of Recommen­dations ITU‑R SM.1541 and ITU‑R SM.329.

NOTE 1 -- Recommendation ITU-R SM.1138, which is incorporated by
reference into the Radio Regulations (RR), deals with the determination
of necessary bandwidth for various emissions. Recommendation ITU-R
SM.853 presents additional information concerning the determination of
necessary bandwidth for certain emissions, including unmodulated pulse
emissions and some digital modulation.

In addition, Recommendations ITU-R SM.1541 (*recommends* 2.3) and ITU-R
SM.329 (*further recommends* 1.4 and 2.3) discuss the necessary
bandwidth for certain emissions for the purpose of determining the
boundary between the OoB and spurious domains.

ANNEX 1

Variation of the boundary between the OoB\
and spurious domains

# 1 Introduction

As stated in *recommends* 2.3 of Recommendation ITU-R SM.1541 and
*further recommends* 2.3 of Recommendation ITU-R SM.329, the boundary
between the OoB and spurious domains, which is generally specified as
being separated from the centre frequency by 250% of the necessary
bandwidth, needs to be modified for narrow-band and wideband (including
multicarrier) systems, and certain other situations. This Annex
provides:

-- a set of guidelines on values of bandwidths across the spectrum at
which the general definition needs to be varied; and

-- a set of known situations in which additional guidelines are
required.

# 2 Boundary variations for narrow-band and wideband systems

For the definition of necessary bandwidth, its applicability to
multichannel or multicarrier transmitters/transponders, and its use in
the fixed and radiodetermination services, see *further recommends* 1.4
of Recommendation ITU-R SM.329.

Figure 1 shows the spurious boundary as a function of necessary
bandwidth, indicating the boundary variations. The normal separation
between the centre frequency and the spurious domain boundary is 250% of
the necessary bandwidth, as shown in Fig. 1, between the vertical dashed
lines.

For some narrow-band emissions, it is appropriate to avoid specifying
OoB and spurious domains in very narrow bandwidths near to the emission,
which will usually be under the control of the same operator. On the
other hand, it is necessary to restrict the linear growth of the OoB
domain versus necessary bandwidth for wideband emissions, in order to
restrict the incursion of the OoB domain into adjacent bands.

Figure 1 shows how the boundary is determined for the narrow-band and
wideband cases. When the necessary bandwidth of the emission is less
than the lower threshold value *BL*, the boundary is a constant
2.5 *BL*. Conversely, when the necessary bandwidth exceeds the upper
threshold value *BU*, the boundary increases at a lower rate, having a
value of 1.5 *BN* + *BU*. Table 1 shows the formulas for the
narrow-band, normal and wideband cases.

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TABLE 1

It should be noted that Table 1 can apply to asymmetric emissions, since
the offset is specified based on the centre of the necessary bandwidth.
For situations where the boundary is not defined in terms of necessary
bandwidth, see § 3.

In the case of narrow-band and wideband systems, the variation of the
spurious boundary also affects the OoB masks specified in Recommendation
ITU-R SM.1541. This is covered in *recommends* 5 of Recommendation ITU-R
SM.1541.

Table 2 provides guidance for determining general values of separation
between the centre frequency of an emission and the beginning of its
spurious domain. A minimum separation applies to the narrow-band case,
while the normal and wideband cases have separate formulas for
determining the boundary.

TABLE 2

Guideline values for frequency separation between the centre frequency\
and the boundary of the spurious domain

*Example 1*: The necessary bandwidth of an emission at 26 MHz is 1.8
kHz. Since 2.5 *BN* is only 4.5 kHz, the minimum separation applies. The
spurious domain begins 10 kHz each side of the centre of the necessary
bandwidth.

*Example 2*: The necessary bandwidth of an emission at 8 GHz is 200 MHz.
Since the wideband case applies for *BN* 100 MHz at that frequency, the
spurious domain begins 400 MHz each side of the centre of the necessary
bandwidth. Using the general separation formula, the OoB domain would
have extended to 2.5 200 MHz = 500 MHz either side of the centre
frequency.

# 3 Situations where additional guidelines are required

The above guidelines are suitable for general application but specific
cases where further guidelines are necessary are given in the following
sections.

## 3.1 Situations where the boundary is not defined in terms of necessary bandwidth

Some systems specify OoB emissions relative to channel bandwidth, or
channel spacing. These may be used as a substitute for the necessary
bandwidth in § 2, provided they are found in ITU-R Recommendations.

## 3.2 Particular service types and bands

The values of frequency separation in Table 2 are selected to cover
most, but not all situations. Rather than set those values at the worst
case in each range, it is more realistic to use a more stringent value,
and list those cases requiring different values separately. Tables 3 and
4 show those cases which have been identified.

TABLE 3

Narrow-band variations for systems or services and frequency bands

TABLE 4

Wideband variations for systems or services and frequency bands

## 3.3 Primary radars in the radiodetermination and other services

According to *further recommends* 2.3 of Recommendation ITU-R SM.329,
the spurious domain emission generally begins at a frequency separation
equal to 250% of the necessary bandwidth, with exceptions for certain
kinds of systems, including those with digital or pulsed modulation.
RR Appendix 3 includes similar provisions. However, it is difficult to
apply the general boundary concept of 250% of the necessary bandwidth to
primary radar stations in the radiodetermination and other services,
such as the meteorological aids service, the space research service, and
the Earth exploration-satellite service.

For the case of primary radar systems, the detailed definition of the
OoB/spurious domain boundary is contained in Annex 8 of Recommen­dation
ITU-R SM.1541.