## 1 Introduction
The IGS data set is based on robot calibrations developed by the Geo++ GmbH [17], and today contains corrections for GPS (L1 = 1575.42 MHz; L2 = 1227.60 MHz) and GLONASS (G1 = 1600.995 MHz; G2 = 1248.06 MHz) frequencies only. In the ANTEX format, these signals are coded as \"G01\", \"G02\", \"R01\" and \"R02\" respectively. The current Geo++ capabilities already allow one to calibrate antennas for 11 GNSS frequencies [18], including Galileo. As reported by [15], the Geo++ has already delivered a set of 37 mean-type calibrations for IGS tests and the repro3 project. Additionally, other centers such as the Swiss Federal Institute of Technology in Zurich [19] are starting robot calibration for Galileo signals, but these products are not yet widely available. Another option is to use the calibrations performed in the anechoic chambers. This method is based on a generated artificial signal, not the real transmitted signals from satellites, but all of the frequencies needed are usually obtained. An example is the calibrations performed by the University of Bonn, Institute of Geodesy and Geoinformation [20]. The compatibility between chamber calibrations and robot calibrations is on a millimeter level [18], and is constantly the subject of discussion and analysis [21; 22; 23; 24]. At present, until IGS releases new products, during the processing of Galileo observations, one has to use individual chamber calibrations. Unfortunately, not all antennas are individually calibrated, and even less have full tables that include all of the Galileo frequencies (E1 = 1575.42 MHz, E5a = 1176.45 MHz, E5b = 1207.140 MHz, E6 = 1278.75 MHz, and E5 = 1191.795 MHz, coded in the ANTEX format as \"E01 \", \"E05\", \"E07\", \"E06\", and \"E08\"). This leads to a situation in which one will need to use GPS-dedicated corrections for the corresponding Galileo frequencies. Generally, GPS corrections for L1 and L2 are used for the Galileo E1 and E5a frequencies, respectively, in many studies [25]. In the case of E1, this is not a major problem, because the frequencies L1 and E1 are equal. Unfortunately, this is not the case for GPS L2 and Galileo E5a, since they differ by 51.15 MHz. As reported by [26], the PCC for E5a differs from the PCC for L2 by roughly a few millimeters. Therefore, using GPS-based PCC values for Galileo frequencies will introduce an error into the estimated values. The full operational capability of Galileo is practically being achieved already, and the expectations of including Galileo observations in many scientific and administrative works are steadily increasing. This applies also to works regarding the maintenance of the reference frame, one of the most precise and demanding products of the International Association of Geodesy (IAG). Of course, the problem of modeling PCO/PVC for Galileo antennas has a much broader meaning. It is related not only with ground antennas, but also with satellite antennas and related products such as orbits or GNSS-derived frame parameters. This paper concerns the problem faced by most ordinary GNSS users and focuses on the impact of using the GPS L2 receiver antenna PCC for the Galileo E5a frequency. Our motivation was to show how big the error in the coordinates can be with this approach. The analyses were conducted both for absolute and relative positioning, using the EUREF Permanent GNSS Network (EPN) as an example.