Mobile Communication / TETRA

TETRA: Technology and Filter Requirements

TETRA (Terrestrial Trunked Radio) is the globally established standard for digital trunked radio, demanding the highest levels of spectral purity and reliability. The technology primarily operates in the frequency ranges of 380 MHz to 400 MHz for public safety and emergency services (PPDR) and 410 MHz to 430 MHz for commercial and industrial applications. Since TETRA networks often operate in close proximity to high-power cellular services like LTE (B31 or B72), the precision of RF filtering is life-critical. Inadequately filtered receiver paths can prevent the decoding of time-critical voice and data signals, which can have fatal consequences in emergency situations. Wainwright Instruments manufactures specialized RF components tailored exactly to the narrow 25 kHz channel spacing and specific modulation methods of TETRA. Our solutions ensure extreme skirt steepness, necessary to safely bridge small duplex gaps of often only 10 MHz between uplink and downlink. To minimize intermodulation in multi-channel systems, we rely on low-loss materials and high-precision manufacturing processes. This ensures maximum receiver sensitivity and robust signal transmission in critical infrastructures where reliability is the top priority.

Typical Deployment Scenarios:

TETRA filters from Wainwright are essential components in communication networks that must guarantee uninterrupted coverage under extreme conditions.

Public Safety (PPDR): In networks for police, fire, and rescue services, our filters in the 380-385 MHz (uplink) and 390-395 MHz (downlink) ranges secure interference-free communication during large-scale operations.
Industrial Campus Networks: For critical infrastructures such as oil refineries or chemical plants, we provide filter solutions that ensure exclusive signal purity against industrial interference in the 410-430 MHz band.
Transport & Logistics: In airport communication systems or rail yards, our components effectively suppress neighboring airband or GSM-R signals to ensure coordination of ground staff.
In-Building & Tunnel Coverage: Within in-building radio systems, our filters prevent feedback and intermodulation in amplifier systems, making radio coverage possible in deep tunnels or bunkers.
Energy Utilities & Smart Grids: Utilities often use TETRA networks for telecontrol; here, our RF solutions protect data integrity against electromagnetic fields in substations.
Military & Border Control: High-performance filters are used in border security systems to optimize the range of TETRA base stations through maximum noise suppression even in difficult terrain.
Public Transport: For fleet management of buses and trains, our components ensure stable radio coverage in urban areas against overloading from commercial mobile networks.
Hybrid Networks (TETRA + LTE): In modern systems combining narrowband TETRA with broadband LTE, our filters enable necessary coexistence and prevent blocking of sensitive TETRA receivers.

Suitable Filter Categories for Mobile Communications / TETRA

The narrowband nature of the TETRA standard requires filters with exceptionally high quality factors (Q-factor) and excellent thermal stability to exclude frequency drift during continuous operation.

Band Pass Filters

Our TETRA Band Pass filters enable precise selection of utilized carrier frequencies in the 380-400 MHz or 450-470 MHz ranges. They are specifically optimized to block neighboring radio services with extremely steep rejection skirts without distorting the narrowband desired signal. By using high-quality cavity resonators, we achieve minimum insertion loss, which directly increases the range of base stations. These filters are designed for high transmit power and guarantee stable performance across wide temperature ranges. Manufacturers of infrastructure components value the mechanical precision that ensures long-term stable tuning of the filter curve.

Manually Tunable Band Pass Filters

For system integration and field measurements in the public safety sector, we offer manually tunable Band Pass filters covering the entire TETRA spectrum. Via precision mechanical tuning elements, the center frequency can be adjusted exactly to the respective operational channel, which is a great advantage for on-site troubleshooting. This flexibility allows technicians to isolate interference sources with frequency precision without carrying multiple fixed filters. The robust construction of our tunable models guarantees high reproducibility of measured values even under harsh conditions at the radio mast or in mobile labs.

Digitally Tunable Band Pass Filters

Electronically reconfigurable filters support modern Software Defined Radio (SDR) concepts in agile TETRA infrastructures. Via digital interfaces, filter profiles can be adjusted in real-time to changing frequency scenarios, which is particularly valuable for gateways in border areas with different band allocations. This digital adjustment enables automated optimization of receiver selectivity upon detection of interferers. Our digitally tunable filters combine the necessary RF quality of Wainwright technology with the flexibility of digital control systems and are optimized for use in test environments and development systems.

Band Reject Filters / Notch Filters

Strong local interferers, such as LTE signals in the 800 MHz range or neighboring FM stations, can overload TETRA receivers; our notch filters provide the necessary protection here. They specifically eliminate the interference source with extremely deep stopband attenuation while the TETRA passband remains unaffected. These filters are essential for maintaining radio coverage at sites with high transmitter density. Due to the extremely narrow stopband bandwidth, the spectral neighborhood is protected, which massively simplifies the planning of complex sites and enables the coexistence of various services. By using our notch filters, the robustness of the infrastructure against external RF influences is massively increased.

Manually Tunable Band Reject Filters / Notch Filters

To suppress unforeseen interference in the field, our manually tunable notch filters are the ideal choice for maintenance teams. The stopband frequency can be fine-tuned directly at the site of installation to effectively mask narrowband interferers, such as those caused by faulty electronics in the vicinity. This flexibility ensures the immediate restoration of communication in critical safety networks. The mechanical construction is optimized for frequent use and provides a stable stopband effect that remains precise even after numerous tuning processes.

Digitally Tunable Band Reject Filters / Notch Filters

In intelligent TETRA networks, digitally tunable notch filters enable an automated response to dynamic interference scenarios. Controlled by monitoring systems, these filters can react to frequency changes in the environment and actively suppress interfering signals. This is particularly valuable in urban smart city environments where the RF spectrum is constantly changing. The remote control capability allows operators to centrally optimize filter characteristics, reducing operating costs and massively increasing the availability of safety radio networks. Their integration into automation concepts for radio optimization enables an autonomous response to interference scenarios.

Monoplexer / Diplexer / Duplexer / Triplexer

Combining multiple TETRA carriers or separating transmit and receive paths requires high-performance multiplexers with extremely high isolation. Our duplexers for the 380 MHz band are optimized for minimum duplex spacing and highest power handling. They allow for the operation of transmitters and high-sensitivity receivers on a shared antenna without crosstalk interfering with communication. Wainwright Instruments manufactures these components with a focus on minimum PIM (Passive Intermodulation), which is a mandatory requirement for capacity expansion at heavily used sites. Our multiplexers are optimized for use in base stations and industrial infrastructure applications.

Absorptive Filters

Absorptive filters play a crucial role in TETRA transmit power stages to ensure transmitter linearity and effectively terminate harmonics. Rather than reflecting unwanted harmonics back to the power amplifier, these filters safely convert them into heat, preventing reflection damage. This is particularly important in TETRA systems with high transmit power to ensure compliance with strict spectral masks. Our absorptive filters are designed for continuous operation and increase the lifespan of the transmission infrastructure by consistently avoiding thermal stress from reflected energy and significantly improving signal purity.