The dongle is programmed to filter out frquecies above and below the designated frequency of operation (1090Mhz +/- 1.5 Mhz for Adsb), but the Cell/Mobile signals are so strong compared to ADS-B signal that this filtering is insufficient, and additional filtering is required to eliminate these XXXL Cell/Mobile signals.
Please see the relative intensities of 1090 Mhz and Cell 850 Mhz & 950 Mhz in scans below:
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You can find the relative strength of signals in your area by scaning using method given here:
Do I Need A Filter?
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