In addition to the GPS and radio data modules themselves, the most important system components in DGPS and RTK applications are optimally adapted VHF or UHF antennas – because this enables a substantially longer range for receiving and sending correction data.
The reliable, long-range reception of correction data by means of VHF and UHF receivers is especially important in regions with poor network coverage. The robust, high-sensitivity modems of the Finnish radio data expert Satel, with a sensitivity of -119 dBm and maximum transmitting power of up to 35W, are ideally equipped for these challenges. In addition, the right VHF or UHF antenna for the GNSS base station and roving receiver also secures significant advantages with respect to range. Satel offers a large spectrum of antennas. They cover a frequency range from 68 MHz to 6,000 MHz, indoor and outdoor applications, MIMO technology and also antennas with an operating range from -40 to +80°C for use in harsh environments.
Due to its long range, the VHF frequency band is widespread in Germany – especially in rural areas. Typically, omnidirectional or directional antennas are used for the base station and omnidirectional receiving antennas for the roving receivers. The base station antennas normally used on land in the VHF band are less than 2-m long and the rover antennas have lengths of less than 1 m. In Germany, the maximum transmitted power for DGPS and RTK signals in the VHF band is limited to 6W ERP, which enables ranges with a radius of up to 20 km. A typical antenna for this area of application is the CA160Y+ model which is available from Welotec.
Especially in urban areas, however, the range advantage of VHF frequencies is cancelled out by a disproportionate rise in the noise level in relation to the frequency. Therefore, EASy modems from Satel for the UHF band (330 to 473 MHz & 869 MHz) are used in urban areas. The user benefits from stable and reliable radio data transmission with substantially smaller antennas (16 to 33 cm). That saves space and weight. Nevertheless, the Satelline-EASy Pro 35W modem can achieve impressive ranges of up to 35 km. In Germany, even with the limitation of the transmitting power to a maximum of 5W ERP for DGPS and RTK signals, transmitting ranges of 10 to 15 km are still possible. Ideal antennas for this range are the PCTP430 series for the roving receiver and the CA450C2 series for the base station.
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