###### Abstract  
Smartphones now dominate the Global Navigation Satellite System (GNSS) devices capable of collecting raw data. However, they also offer valuable research opportunities in intentional jamming, which has become a serious threat to the GNSS. Smartphones have the potential to locate jammers, but their robustness and sensitivity range need to be investigated first. In this study, the response of smartphones with dual-frequency, multi-constellation reception capability, namely, a Xiaomi Miss, a Xiaomi 11T, a Samsung Galaxy S20, and a Huawei P40, to various single- and multi-frequency jammers is investigated. The two-day jamming experiments were conducted in a remote area with minimal impact on users, using these smartphones and two Leica GS18 and two Leica GS15 geodetic receivers, which were placed statically at the side of a road and in a line, approximately 10 m apart. A vehicle with jammers installed passed them several times at a constant speed. In one scenario, a person carrying the jammer was constantly tracked using a tacheometer to determine the exact distance to the receivers for each time stamp. The aim was, first, to determine the effects of the various jammers on the smartphones' positioning capabilities and to compare their response in terms of the speed and quality of repositioning with professional geodetic receivers. Second, a method was developed to determine the position of the interference source by varying the signal loss threshold and the recovery time on the smartphone and the decaying carrier-to-noise ratio (CNR). The results indicate that GNSS observations from smartphones have an advantage over geodetic receivers in terms of localizing jammers because they do not lose the signal near the source of the jamming, but they are characterized by sudden drops in the CNR.  
GNSS; jamming; smartphones; Xiaomi Miss; Xiaomi 11T; Huawei P40; Samsung S20 20000  
running the Android N (\"Nougat\" = version 7) operating system would be accessible to developers [1; 2; 3]. Since then, details of their code pseudo-range, carrier-phase, Doppler shift, carrier-to-noise density ratio (CNR), and navigation message have become available. An analysis of the raw data from low-cost receivers provides a valuable insight into the effects on observations, which can be used to solve the current problem of attacks on GNSS signals.  
As earlier studies at the University of Ljubljana [4; 5; 6] have shown, professional geodetic receivers usually do not acquire measurements at low CNR values when they are affected by jamming. This has a great advantage, since the position is correctly determined. On the other hand, raw observations are not available during the jamming to locate the source of the interference. Since the authors reported that smartphones are not able to detect jamming or spoofing [7; 8] but continue receiving data even when they are jammed and/or spoofed, the basic idea of this study was to investigate the smartphones' behavior with respect to geodetic GNSS receivers in the presence of various jammers. Based on the known position of the GNSS devices and, in one scenario, also the positions of the jammers obtained using a tacheometer positioning system (TPS), the goal was to develop an improved fingerprint of the specific behavior of each smartphone and its position anomalies during and after jamming periods.