dBm – what does the unit mean and why is it crucial for RFID?

Introduction: Signal strength plays a central role in RFID technology, radio communication, and industrial data transmission. Whether a transponder is read reliably, bulk detection works stably, or reading errors occur depends largely on the transmitted power. One of the most important parameters in this context is dBm.

The term dBm describes the absolute power of a signal and is a technical term used particularly in RFID technology and radio communication. dBm is used in RFID readers, antennas, transponders, and radio interfaces, among other things. Anyone who plans, operates, or optimizes RFID systems cannot ignore this unit.

What is dBm?

dBm stands for decibel milliwatt (decibel relative to one milliwatt). It is a logarithmic unit used to indicate electrical power, regardless of voltage or current. Wi-Fi signal strength is most commonly measured in decibels per milliwatt (dBm).

The reference value is always:

0 dBm = 1 milliwatt (mW)

Here, zero is the scale value for the reference point of the measurement.

All other dBm values indicate how strong the power is in relation to this reference value – either higher (positive dBm values) or lower (negative dBm values). Signal strength is usually rated on a scale from approximately -100 to 0 dBm, with higher values indicating better signal quality.

Why is dBm used instead of watts?

In radio and RFID technology, power levels often vary greatly, ranging from very low to very high. A linear representation in watts would be confusing. The purpose of using dBm instead of watts is to present power values in a clear and comparable way, in particular to facilitate the calculation and evaluation of signal strengths in different application scenarios.

The logarithmic representation in dBm offers clear advantages:

• Large power ranges can be represented compactly
• Attenuation, amplification, and losses can be easily added or subtracted
• Signal comparisons become much easier
• Industry standards and norms are based on dBm specifications

This representation is essential, especially for RFID systems, as many influencing factors and environmental conditions interact here. The power values are output in dBm to enable easy comparison and further processing of the data in software and system processes.

Overview of typical dBm values

Here are some practical examples for better classification:

• 0 dBm → 1 mW
• 10 dBm → 10 mW
• 20 dBm → 100 mW
• 30 dBm → 1 W
• –30 dBm → very weak signal (typical for received RFID responses)

Example: The conversion from dBm to watts (W) is calculated using the formula: P(W) = 10^(dBm/10) / 1000.
A value of 20 dBm therefore corresponds to 0.1 W.

A perfect signal is -30 dBm. A value of -50 dBm is considered excellent signal strength, while -60 dBm is considered good. -67 dBm is the minimum for a reliable connection and all online services that require a stable connection. -70 dBm is the minimum value for reliable online services. The closer the dBm value is to zero, the stronger the signal.

Even small changes in the dBm value can result in significant differences in performance – a crucial factor in terms of range, signal strength, and read reliability.

dBm in the RFID environment – why this unit is so important

Several performance parameters interact in RFID systems:

• Transmission power of the RFID reader
• Antenna gain
• Cable losses
• Material influences (metal, liquids, glass)
• Sensitivity of the RFID chip

The combination of these different components and performance parameters determines the versatility and efficiency of modern RFID systems.

All these factors are ultimately measured in dBm and affect the quality of the signal. Problems such as electromagnetic interference, anti-collision issues, or data protection risks can impair signal transmission and have a negative impact on dBm values and system reliability.

Transmission power of the reader

RFID readers transmit with a defined output power, usually in the range of 20 to 33 dBm (depending on region, standard, and manufacturer). The transmission power is emitted in the form of electromagnetic waves that are transmitted from the reader to the transponder. For comparison: Typical transmission powers of WLAN devices are often in the range of 17–20 dBm, which corresponds to 50–100 mW. This power determines how much energy reaches the transponder.

Transponder backscatter signal

The RFID chip reflects the received signal back to the reader, which in this context acts as the receiver of the backscatter signal. This response signal is often in the range of –40 dBm to –70 dBm – extremely weak and highly dependent on the label design, antenna type, and environment.

This shows how important an optimized inlay, antenna design, and carrier material are to ensure a stable connection and high reading accuracy.

Influence of dBm on range and read reliability

A higher dBm value does not automatically mean a better system. The interaction of all components is crucial:

• Excessive transmission power can lead to multiple reflections and interference
• Insufficient power reduces the range and stability of the connection; if the dBm value falls below a certain threshold, the connection may be impaired or become unstable
• The signal strength provides information about the quality and reliability of the connection and indicates whether the network is stable enough for various applications
• Materials can attenuate or distort the signal and affect signal quality.
• Antenna position, design, and frequency band affect effective field distribution

.

This is precisely why special RFID label designs, such as those with offset antennas or optimized geometry, are indispensable in many applications.

dBm and RFID labels from PMG

When developing RFID labels, tags, and inlays, PMG takes dBm-relevant parameters into account right from the start: RFID tags play a central role here, as they are responsible for signal transmission in the system and have a significant influence on overall performance.

• Optimized antenna geometries for stable coupling and high reception strength
• Adaptation to difficult surfaces such as metal or liquids
• Uniform field distribution for reproducible readability
• Compatibility with common reader performances and frequency bands

In addition to identification, RFID labels also enable the marking of products or contents, so that, for example, information can be edited or highlighted directly on the label.

The aim is to ensure reliable identification even at low reception levels – regardless of whether it is for logistics, industry, smart cabinets, or retail applications.

Typical areas of application with dBm relevance

dBm plays a role wherever RFID systems need to function precisely and reliably:

• Logistics and warehouse management with bulk recording
• Smart cabinets and medical technology
• Industrial and production environments
•  Automated material flows
• RFID labeling on critical materials and products

Companies benefit particularly from RFID solutions to make their working environments, meeting rooms, or production processes more efficient and modern.

RFID technology is also used to identify and track people, for example in access control or security applications, whereby data protection aspects must also be taken into account.

In these scenarios in particular, the correct interpretation of performance is decisive for success, connection quality, and error measurements.

Conclusion: dBm as a key parameter for reliable RFID systems

dBm is much more than a technical parameter. The unit describes the basis of all stable radio and RFID communication. In this article, you will learn everything you need to know about dBm and the use of RFID systems. If you want to optimize range, read reliability, and process stability, you need to understand dBm values, calculate them correctly, and interpret them correctly.

Through well-thought-out RFID label concepts, material-adapted designs, and targeted consideration of dBm values, reliable results can be achieved even in demanding environments. RFID systems offer valuable assistance in this regard by making processes more efficient and enabling quick access to important information.

FAQs

What does dBm mean and why is this unit important?

dBm stands for decibel milliwatt and describes the power of a signal in relation to one milliwatt. This logarithmic unit is particularly important in radio and RFID technology, as it clearly represents large power ranges and simplifies the calculation of attenuation, amplification, and signal strength checks.

How does the dBm value affect the range and signal quality of an RFID system?

The dBm value indicates the strength of the transmission power or the received signal. A higher dBm value does not automatically mean better range, as excessive power can cause interference. The interaction of transmission power, antenna gain, frequency band, and environmental conditions is crucial for optimal range, stable connection, and reliable reading.

What is the difference between positive and negative dBm values?

Positive dBm values are above 0 dBm (1 milliwatt) and indicate power above this reference value, while negative values are below this and represent lower power. Received signals, such as those from RFID transponders or WLAN, are usually in the negative range because they are very weak. The RSSI value (Received Signal Strength Indicator) also indicates the received signal strength in dBm and helps to evaluate the connection quality.

How can I convert dBm values to watts, and what do the numbers mean?

The conversion from dBm to watts is done using the formula: Power (watts) = 10^((dBm - 30)/10). Here, 0 dBm corresponds exactly to 1 milliwatt (mW). Small changes in the dBm value lead to large differences in power. For example, an increase of 3 dB means a doubling of power, while a decrease of 3 dB means a halving.

What factors influence dBm values and reception strength in RFID and WLAN?

In addition to the transmission power of the router or reader, antenna gain, cable losses, frequency band, material influences such as metal or liquids, the environment, and the sensitivity of the receiver play an important role. Together, these factors determine the signal strength, the quality of the connection, and thus the reliability of communication.