High-Performance ISM Radio Band Transceiver, Receiver and Transmitter – Sub 1GHz, 2.4GHz & 5GHz solutions for industrial applications

ISM Band utilisation for wireless communication

The ISM radio bands are portions of the radio spectrum reserved internationally for industrial, scientific and medical (ISM) purposes other than telecommunications.

Typical European ISM frequencies are 433MHz, 868MHz, for worldwide usage 2.4GHz.

Despite the intent of the original allocations, in recent years the fastest-growing use of these bands has been for short-range, low power wireless communications systems, since these bands are often approved for such devices which can be used without a government license, as would otherwise be required for transmitters; ISM frequencies are often chosen for this purpose as they already have interference issues.

Cordless phones, Bluetooth devices, near field communication (NFC) devices, garage door openers, baby monitors and wireless computer networks (Wi-Fi) may all use the ISM frequencies, although these low power transmitters are not considered to be ISM devices.

Product ranges in ISM proprietary radios and SoCs

Sub 1GHz ISM Radios and SoCs
Amiccom
Sub 1GHz ISM Radios and SoCs

Low power radio transceivers/receivers/transmitters for Sub 1GHz wireless applications like smart meter reading.

2.4GHz ISM Radios and SoCs
Amiccom
2.4GHz ISM Radios and SoCs

Low power radio transceivers/receivers/transmitters for various 2.4GHz wireless applications

5GHz ISM Radios and SoCs
Amiccom
5GHz ISM Radios and SoCs

Low power radio transceivers for wireless applications in the 5GHz frequency band.

FAQs about ISM Radios (Industrial, Scientific and Medical) and SRD (Short Range Devices)

ISM (Industrial, Scientific and Medical) refers to radio frequency bands originally designated for industrial, scientific, and medical applications, which can be utilized on a non- non-licenced base. Devices operating within ISM bands only require a general frequency allocation, rather than individual licences. Some ISM bands are also widely used for audio, video, and data transmission – such as Wi-Fi and Bluetooth.

Usage of these bands is governed by general frequency assignments published by national regulatory authorities such as the German “Bundesnetzagentur”.

The following frequency ranges are globally allocated for ISM use:

  • 6.765 MHz – 6.795 MHz
  • 13.553 MHz – 13.567 MHz
  • 26.957 MHz – 27.283 MHz
  • 40.66 MHz – 40.70 MHz
  • 433.05 MHz – 434.79 MHz
  • 902 MHz – 928 MHz
  • 2.4 GHz – 2.5 GHz
  • 5.725 GHz – 5.875 GHz
  • 24 GHz – 24.25 GHz
  • 61 GHz – 61.5 GHz
  • 122 GHz – 123 GHz
  • 244 GHz – 246 GHz

In some cases, the use of these bands may still require authorisation from regional authorities. In Germany, the 9–10 kHz range and the 150 MHz frequency are also allocated as ISM bands. Common applications include microwave ovens, Wi-Fi, Bluetooth, baby monitors, radar motion detectors, remote switches and more.

SRD (Short Range Devices) refer to radio applications with low power and limited range. These frequency bands are standardised in many countries and are used for remote controls, sensors and smart home systems. SRDs are radio devices intended for general use, characterised by low transmission power and range.

Compliance with national and international standards is required, indicated e.g. by the CE marking.

SRDs operate across a variety of frequencies depending on region and application.

Here are the most important frequency ranges:

  • 6.765–6.795 MHz: Max. magnetic field strength of 125 µA/m at 10 m.
  • 13.553–13.567 MHz: 10 mW ERP.
  • 26.957–27.283 MHz: 10 mW ERP.
  • 40.660–40.700 MHz: 10 mW ERP.
  • 149.025–149.1125 MHz: Applications like Freenet in Germany.
  • 169.400–169.8125 MHz: Varying power levels (10 mW to 500 mW).
  • 433.05–434.79 MHz: Formerly LPD; now SRD with restrictions in Europe.
  • 446.0–446.2 MHz: PMR radio (Personal Mobile Radio) with analogue and digital channels (up to 500 mW ERP). -863–870 MHz: Split into sub-bands for various applications.
  • 2.4 GHz and above: Wireless technologies such as Wi-Fi.

  • ISM bands were originally intended for industrial, scientific, and medical use but are now commonly employed for general communications.
  • SRD bands are specifically reserved for short-range radio applications and are subject to more restrictive limits of transmission power and bandwidth.

Though licence-free, several restrictions apply:

  • Maximum transmission power (e.g., typically 25 mW at 868 MHz in Europe).
  • Duty cycle limitations (i.e. restricted transmission time).
  • Regional frequency regulations.
  • Compliance with CE (Europe) or FCC (USA) standards.

Legal restrictions on the transmit power of ISM and SRD devices vary by frequency band and region. Here are the most important requirements:

ISM Bands: Transmission power in ISM bands is limited by national and international regulations to avoid interference with other services.

Examples:

  • 2.4–2.5 GHz: Max. 100 mW (20 dBm) for Wi-Fi and Bluetooth (Europe).
  • 433.05–434.79 MHz: Max. 10 mW ERP (Europe).
  • 5.725–5.875 GHz: Max. 25 mW (Europe).
  • 13.553–13.567 MHz: Max. 10 mW ERP.

ISM devices must meet electromagnetic compatibility (EMC) requirements and avoid interfering with other services.

SRD Bands: SRD devices have specific limitations regarding transmit power or field strength, depending on the frequency band:

  • 6.765–6.795 MHz: Max. 42 dBµA/m at 10 m.
  • 863–870 MHz: Max. 25 mW ERP (e.g., smart home devices).
  • 446 MHz: Max. 500 mW ERP for PMR radios.
  • 24–24.25 GHz: Max. 100 mW ERP.

Devices must accept interference from other services and operate without exclusive rights to the spectrum access.

In some frequency ranges, additional technical requirements apply, such as:

  • Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC) in the 5 GHz band.
  • Indoor-only operation at some bands (e.g. 5.150–5.350 GHz).

ISM and SRD bands are used for a variety of applications. Here are some typical areas of use:

ISM Bands: Wireless communication: Wi-Fi, Bluetooth, Zigbee, NFC, LoRa, Z-Wave, Thread.

  • RFID: Used at 13.56 MHz and 915 MHz for access control, logistics, and payments.
  • Medical tech: Diathermy, hyperthermia therapy, microwave ablation.
  • Household: Microwave ovens, induction heating.
  • Industry: RF welding, radar systems.

SRD Bands:

  • Security: Smoke detectors, motion sensors, personal alarms.
  • Automotive: Car key fobs, garage openers, vehicle radar.
  • Remote control: Wireless thermostats, model control, home automation.
  • Medical implants: Pacemakers, wireless health sensors.
  • Telemetry: Smart meters, traffic systems, remote monitoring.

Both ISM and SRD bands offer low-power, licence-free options for short-range communication.

ISM and SRD bands are subject to various interference and limitations caused by technical, regulatory, and physical factors. Here are the key points:

Interference:
  1. Electromagnetic Interference (EMI):
    • ISM devices, such as microwave ovens or industrial RF applications, generate strong electromagnetic fields that can disrupt radio communication within the same frequency bands.
    • SRD devices may interfere with each other, especially when spectrum usage is high and synchronisation is lacking, leading to channel access collisions.
  2. Overload due to High Usage Density:
    • Heavily used bands, such as the 2.4 GHz ISM band, are often contested between Wi-Fi, Bluetooth and other applications, which can impact communication reliability.
  3. Spurious Emissions:
    • Devices may emit unintended signals outside their designated frequency bands/channels, causing interference with adjacent services. Regulations strictly limit such emissions.
  4. Channel Access Collisions:
    • In SRD bands, signal collisions can happen due to unsynchronised spectrum access methods (e.g. when independent radio systems use the same channel in close vicinity to each other), hence reducing the efficiency of spectrum usage.
Limitations:
  1. Limited Transmission Power:
    • The maximum transmission power is limited depending on the frequency band (e.g. 100 mW in the 2.4 GHz band for ISM devices and up to 25 mW in certain SRD bands).
  2. Duty Cycle Limits:
    • SRD devices are only allowed to transmit for a limited time (e.g. a maximum of 10% of the time in certain bands) to minimise interference.
  3. Frequency Restrictions:
    • Some frequency ranges are exclusively reserved for dedicated services or are subject to strict limitations. I.e., they cannot be used by “non-specific” short range devices.
  4. Technical Requirements:
    • Features like frequency agility (Adaptive Frequency Allocation) or "Listen Before Talk" must be implemented to improve coexistence with other devices.
  5. No Protection Rights:
    • Users of ISM bands are not protected from interference caused by other ISM devices; they must tolerate such interference.

In summary, the use of ISM and SRD bands requires careful planning to minimise interference and ensure compliance with regulatory requirements.

As examples, the following lists show the maximum transmit power or field strength limits, respectively, for the most common ISM and SRD bands in Europe:

ISM Bands:

  • 6.765–6.795 MHz: 42 dBµA/m @ 10 m
  • 13.553–13.567 MHz: 10 mW ERP or 42 dBµA/m
  • 26.957–27.283 MHz: 10 mW ERP or 42 dBµA/m
  • 433.05–434.79 MHz: 10 mW ERP
  • 2.4–2.5 GHz: 100 mW (20 dBm)
  • 5.725–5.875 GHz: 25 mW
  • 24–24.25 GHz: 100 mW ERP
  • 61–61.5 GHz: 100 mW ERP

SRD Bands: Same values as above, in case of overlapping.

  • 863–870 MHz:

  • General: 25 mW ERP

  • 869.4–869.65 MHz: 500 mW ERP (10% duty cycle)

  • 446 MHz (PMR446): 500 mW ERP

  • 57–64 GHz: 100 mW ERP for broadband data

Restrictions: The use of these bands is subject to additional requirements such as duty cycle limits (e.g. max. 1% or 10% transmission time) and interference mitigation techniques (e.g. DFS and TPC).

The range depends on the frequency, transmission power, receiver sensitivity, environmental conditions, antenna characteristics and other factors. Walls, buildings and interference can significantly reduce the range.

A specific range can only be stated under clearly defined conditions.

The range can be calculated theoretically using the link budget and the "free space formula". However, the actual achievable range must be verified with the specific RF modules in practice.

Optimizing radio traffic in the ISM and SRD bands can be achieved through various technical and organizational measures. Here are the most important approaches:

Technical measures:

  1. Antenna Implementation:
    • Selection of an antenna, which is suitable for and works efficiently in the intended application environment
    • Optimization of the antenna installation within the application environment
  2. Antenna Matching:
    • Proper matching between the antenna and the transceiver’s RFIO is also a key factor for a good and efficient radio communication
    • The antenna matching should be verified and optimized in the final application environment
  3. Frequency Management:
    • Dynamic Frequency Selection (DFS) and spectrum sensing techniques can minimise interference by identifying and using free channels.
  4. Optimisation of Frequency Hopping Techniques:
    • Frequency Hopping Spread Spectrum (FHSS) reduces interference by distributing transmissions over multiple carrier frequencies. This is especially useful at heavily occupied bands, such as the 2.4 GHz band.
  5. Duty Cycle Limits:
    • Limiting transmission time (e.g. 1% or 10%) reduces interference and allows multiple devices to coexist within the same band.
  6. Signal Filtering:
    • The use of high-quality filters can help to reduce unwanted emissions in transmitters and to improve the selectivity of receivers.
  7. Adaptive Modulation and Coding:
    • Adapting modulation and coding schemes to the channel conditions increases communication robustness.

Organisational measures:

  1. Coexistence Planning:
    • Before installing wireless systems, potential interference from other radio services should be analysed and minimised.
  2. Spectrum Monitoring:
    • Regular supervision of the used frequencies ensures that no unauthorised interference is occurring.
  3. Standards Compliance:
    • Compliance with international and – if applicable – national standards, such as CE marking and specific frequency allocations, ensures interference-free operation.

Application Examples

  • In industrial applications, LPWAN technologies such as LoRa can be optimised through effective frequency management.
  • For Bluetooth and WLAN devices, working in parallel at the 2.4 GHz band, techniques such as DSSS and FHSS (Direct Sequence and Frequency Hopping Spread Spectrum, repsectively) help to reduce interferences.

These measures can significantly enhance the efficiency and reliability of wireless communication in ISM and SRD bands.