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Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →To clarify a spurious-emissions result, first identify which unwanted-emission category it represents, where the applicable standard places the spurious-domain boundary, and whether the limit is for conducted power or a radiated field. There is no universal limit or test setup: requirements depend on the transmitter, radio service, jurisdiction, and governing standard. The ETSI figures below are only an example for E-UTRA user equipment.
1. Define a spurious emission before diagnosing the plot
ITU-R Recommendation SM.329-13 (September 2024) defines a spurious emission as an emission outside the necessary bandwidth whose level may be reduced without affecting the information being transmitted. Examples include harmonics, parasitic emissions, intermodulation products, and frequency-conversion products.
This definition helps distinguish a genuine unwanted emission from energy that is part of the intended transmission. A visible peak alone does not tell you which category it falls into; you need the signal’s necessary bandwidth and the applicable standard’s definitions.
2. Distinguish spurious emissions from out-of-band emissions
Out-of-band emissions occur immediately outside the necessary bandwidth as a result of the modulation process. Spurious emissions are a separate category. Together, the two categories make up unwanted emissions; as ITU-R puts it, “Unwanted emissions consist of spurious emissions and out-of-band emissions.”
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The distinction matters because the applicable limits and measurement procedures may differ. Do not label every unwanted spectral component a spur or apply a spurious-domain limit to an out-of-band result without checking the governing standard.
3. Treat 250% as a general boundary guide, not a universal cutoff
ITU-R SM.329-13 gives a general principle: the spurious domain begins at a frequency separation of 250% or more of the necessary bandwidth from the center frequency. It is not a single fixed frequency applicable to every transmitter.
The separation can depend on the modulation, maximum digital bit rate, transmitter type, and coordination factors. Some systems may require a different boundary. For a compliance decision, use the boundary specified by the standard for the particular service and equipment rather than applying the 250% guide mechanically.
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4. Check what quantity the limit measures—and where
A limit may be stated as power supplied to the antenna feeder within a reference bandwidth, or as field strength or power flux density at a location. These are different quantities, measured using different setups.
- Conducted measurement: measures power at an antenna feeder or port. It requires suitable access and a method consistent with the applicable standard.
- Radiated measurement: measures a field or power flux density at a location, under specified site and geometry conditions.
Do not compare a conducted power result directly with a radiated field result. Any conversion depends on the applicable method and assumptions, including antenna and site characteristics. For space-station active antennas, a port measurement may miss emissions generated within the antenna; a radiated measurement may therefore be needed.
5. Choose selective equipment and settings suited to the test
ITU-R identifies a selective receiver or spectrum analyzer as possible equipment for measuring spurious power supplied to an antenna and cabinet radiation. Either can be appropriate only if its capabilities and settings suit the measurement.
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- Confirm the instrument covers the required frequency range and has sufficient sensitivity for the limit being assessed.
- Set the measurement bandwidth, resolution bandwidth, detector or weighting, and averaging as required by the governing procedure.
- Check that the input can tolerate the transmitter signal and that the instrument has enough dynamic range to measure weak emissions without overload.
- Use calibration with traceability appropriate to the test, and apply any required correction factors.
ITU guidance includes resolution-bandwidth recommendations and mean and peak weighting functions. Depending on the signal type and bandwidth, a result may need integration or bandwidth normalization. A spectrum trace without suitable settings and calibration is not, by itself, evidence of compliance.
6. Keep the transmitter fundamental from masking or distorting the spur
A strong fundamental can overload the measurement chain or obscure low-level emissions. ITU-R describes conducted measurement approaches that address this problem; the selected procedure should match the applicable standard.
With a fundamental-rejection filter
One approach uses a rejection filter to reduce the fundamental before measuring the spurious component. The measurement components or complete chain must be calibrated as prescribed. ITU-R also describes a substitution approach using a calibrated generator.
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Without a rejection filter
A method without a rejection filter is also described. It uses calculations based on the measured fundamental, measured spur, and coupling factor where applicable. Follow the detailed procedure, including its calibration and correction requirements; a simple analyzer reading should not be treated as a substitute for the prescribed method.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.7. Apply equipment-specific limits only within their stated scope
ETSI EN 301 908-13 V13.3.1 (October 2024) provides an example for E-UTRA user equipment. Its general spurious-emission levels are:
| Frequency range | Example limit | Reference bandwidth |
|---|---|---|
| 9 to 150 kHz | −36 dBm | 1 kHz |
| 150 kHz to 30 MHz | −36 dBm | 10 kHz |
| 30 MHz to 1 GHz | −36 dBm | 100 kHz |
| 1 GHz to 12.75 GHz | −30 dBm | 1 MHz |
These values belong to the named standard and its E-UTRA user-equipment scope; they are not universal radio limits. The standard also contains separate protected-band coexistence requirements. Check the complete applicable standard for the measurement conditions and any additional requirements before deciding whether a result passes.
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- Frequency Range from 9 kHz up to 2.1 GHz
- -161 dBm/Hz Displayed Average Noise Level (Typ.)
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8. Make the result repeatable and reviewable
A useful compliance record lets another person understand exactly what was measured and reproduce the setup. Record:
- the governing standard and version;
- transmitter state and modulation;
- frequency span and measurement reference bandwidth;
- detector, weighting, and averaging settings;
- whether the measurement was conducted or radiated, and the method used;
- calibration status and applied correction factors; and
- the measurement upper-frequency limit and the reason for choosing it.
ITU-R notes that emissions may exist throughout the radio spectrum, while practical constraints can limit the upper frequency measured. State the range actually covered and the rationale; do not imply that unmeasured frequencies were checked.
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