RF INTERFERENCE AUDIT

BTESA provides RF engineering services for interference analysis Andorra Telecom’s TETRA Network 

BTESA has provided specialized engineering services to Andorra Telecom for the detection, analysis, and identification of interferences in the uplink band of its TETRA network, a critical infrastructure for the country’s communications. 

The network was experiencing recurring interference issues that triggered alarms at various sites. Although Andorra Telecom had previously engaged specialized companies, the exact source of the interferences had not been clearly identified, nor had definitive solutions been implemented. 

To address the issue rigorously, the project was structured into two complementary measurement campaigns conducted throughout 2025, each with specific objectives and methodologies. 

First Campaign: Radio Environment Analysis 

The first campaign, carried out between August and September 2025, focused on analyzing the radio environment and identifying potential interfering signals within the TETRA uplink band (380–385 MHz). 

During this phase, BTESA carried out on-site IQ captures, continuous and threshold-based measurements, detailed spectral analysis, and exploratory demodulation processes in the laboratory. Additionally, a temporal correlation was conducted between the detected signals and alarm logs and call data provided by the operator. 

This approach enabled differentiation between persistent and intermittent interferences and allowed verification of external signals against the actual network behavior. 

The results revealed the presence of genuine external interferences, particularly associated with harmonics of FM radio transmissions in specific environments. At the same time, evidence of internal phenomena was identified, potentially related to system nonlinearities, insufficient isolation between transmission and reception, degraded connectors or passive components, and possible passive intermodulation effects. 

These findings highlighted the need for a second-level investigation, focusing not on the radio environment but on the RF infrastructure deployed at the sites. 

Second Campaign: RF Infrastructure Characterization 

The second campaign, conducted in December 2025, focused on a detailed analysis of the RF chain at several sites within Andorra Telecom’s network. 

During the technical visits, BTESA reviewed and characterized various infrastructure elements, including base transceiver stations (TBS), duplexers, multicouplers, cabling, jumpers, connectors, adaptations, and, as far as possible, the radiating system. 

Measurements were performed using a combination of spectrum analyzers, vector network analyzers, and parallel monitoring with RF Catcher, allowing assessment of the system’s real operational behavior. 

Results and Conclusions 

Thanks to these two complementary campaigns, BTESA provided Andorra Telecom with a solid technical foundation to understand the origin of the interferences, considering both interactions with external signals present in the radio environment and the internal behavior of the RF infrastructure. 

The work allowed root-cause hypotheses to be narrowed down and defined multiple courses of action for mitigating the issue, verifying certain network elements, and improving operational robustness. 

Through this project, BTESA demonstrates its ability to perform advanced diagnostics in critical communication networks, combining fieldwork, spectral analysis, hypothesis validation, and specialized knowledge of TETRA systems and RF behavior in complex radio environments.