We know that a local cellphone tower will kill your ADS-B receiver unless yo have antenna filters - Has anyone looked at the other side of this … the interference that may come from the cellphones in pockets?
There are many cell frequencies – it’s the 950 MHz stuff that’s going to cause the most problems.
As far as interference from cell phones, I haven’t noticed any on my site(s) from our mob. But we’re 20 to 30 feet below the antennas, which is a really good place for signal isolation (or really bad place for signal pickup).
If you can see your ADS-B antenna at eye level and you’re using a cell phone, yeah, I think the chances of signal interference are pretty good, no matter what band your cell phone works on, unless your SDR/amplifier input is filtered. We know that strong signals overload the SDR input, generating all kinds of trouble.
If the antenna is up on the roof and you’re 20 feet below it, I don’t think there are going to be problems, unless you have a really, really omni antenna. Ground-planes, cantennas, franklin-ground planes, all cut off signal below the antenna horizon (ground plane).
If you’re going to start doing stubs, try a shorted quarter wave stub at 1090 MHz – a shorted quarter wave stub acts as a bandpass filter (high impedance at resonance) where the open quarter wave acts as a low impedance at resonance.