10/4/2023 0 Comments Analysis of radi osThe VSWR display in the right graph measures the same antenna and the amplitude scale has been setup to match the scale of the Return Loss measurement. The Return Loss amplitude scale is setup to go from 0.5 dB to 28 dB. The trace in picture 1 shows a Return Loss measurement of a cellular antenna matched between 806-869 MHz. The scale of a VSWR is usually defaulted to setup between 1 and 65. Antenna manufacturers typically specify the match in VSWR. A more realistic match for a cable & antenna system is in the order of 1.43 (15 dB). A perfect or ideal match in VSWR terms would be 1:1. If the match is not perfect, the peaks and valleys of the returned signal will not align perfectly with the transmitted signal and the greater this number is, the worse the match is. VSWR measures the ratio of voltage peaks and valleys. In contrast to Return Loss, VSWR displays the match of the system linearly. The return loss scale is normally set up from 0 to 60 dB with 0 being an open or a short and The return loss view is usually preferred because of the benefits with logarithmic displays one of them being that it is easier to compare a small and large number on a logarithmic scale. The return loss displays the ratio of reflected power to reference power in dB. Return Loss and VSWR both display the match of the system but they show it in different ways. While different systems have different acceptable return loss limits, 15 dB or better is a common system limit for a cable and antenna system. If the return loss is 10 dB, 10% of the power is returned. This extra energy returned to the transmitter will not only distort the signal but it will also affect the efficiency of the transmitted power and the corresponding coverage area.įor instance, a 20 dB system return loss measurement is considered very efficient as only 1% of the power is returned and 99% of the power is transmitted. A poorly matched antenna will reflect costly RF energy which will not be available for transmission and will instead end up in the transmitter. If problems show up during this test, there is a very good likelihood that the system has problems that will affect the end user. These measurements show the user the match of the system and if it conforms to system engineering specifications. The return loss and VSWR measurements are key measurements for anyone making cable and antenna measurements in the field. Verify Cable Insertion Loss From Ground Level Another major benefit of analyzing the system using RF sweeps is that antennas are tested at their correct operating frequency and the signal will go through frequency selective devices such as filters, quarter-wave lightning arrestors, or duplexers which are common to cellular antenna systems. Analyzing the data in the frequency domain enable users to find small degradations or changes in the system and thus can prevent severe system failures. This technology uses RF frequencies to analyze the data, providing the ability to locate changes and degradations at the frequency of operation. Most modern analyzers used today to characterize the antenna system use the Frequency Domain Reflectrometry (FDR) technology. The purpose of this white paper is to cover the fundamentals of the key measurements of cable and antenna analysis Return Loss, Cable Loss, and Distance-To-Fault (DTF). It is the role of the field technician to troubleshoot the cable and antenna system and ensure that the overall health of the communicationįield technicians today rely on portable cable and antenna analyzers to analyze, troubleshoot, characterize, and maintain the system. While a problematic base station can be replaced, a cable and antenna system is not so easy to replace. From a carrier standpoint, this could eventually result in loss of revenue. Degradations and failures in the antenna system may cause poor voice quality or dropped calls. The cable and antenna system plays a crucial role of the overall performance of a Base Station system.
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