The space around ADS-B antenna contain not only 1090 MHz signals, but also lot of other signals at different frequencies. The closer the frequency of a signal to 1090 MHz, your ADS-B antenna picks it stronger. For example if there are three signals of equal strength, one at 144 MHz, 2nd at 850 MHz and 3rd at 950 MHz, the ADS-B antenna will pick 950 MHz one the strongest, 850 MHz one a bit less stronger, and 144 MHz one much fainter.
As the Cell/Mobile/Pager signals exist in the range 850 MHz to 1200 MHz, these are picked strongly by ADS-B antenna and this mixture is fed to the receiver, overloading its front end tuner. To overcome this situation, a hardware called “Filter” is used. As its name shows, it filters out unwanted signals and passes a narrow band of frequency say 1075 MHz to 1150 MHz, blocking most Cell/Mobile/Pager signals from reaching the receiver.
In order to determine if a filter is needed or not, it is necessary to scan frequencies in the range 800 MHz to 1200 MHz. If the scan shows very few and weak interfering signals, adding a filter will not give any appreciable improvement. On the other hand if the scan shows a lot of strong interfering frequencies, adding a filter will give substantial improvement in ADS-B 1090 MHz reception.
Software developers have developed softwares which use (DVB-T+ADS-B Antenna) to perform this scan. There are following two ways it can be done. Please click the options below to see the details.
DVB-T is plugged into Raspberry Pi (or is plugged into a Desktop/Laptop running Linux Debian/Ubuntu)
DVB-T is plugged into a Windows Computer. Using GUI software rtlplan.exe
DVB-T is plugged into a Windows Computer. Using Command Line Terminal