Interference from Cellphones


#1

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?

Should we all have 1090Mhz passband filters?


#2

I have my own bias on bandpass filters…

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).

bob k6rtm


#3

Luckily in the US there aren’t any cell phones using the 900mhz range. I remember hearing Nextel had some 900 stuff but that’s been done with for a while now.


#4

We do have Pagers at 929-931Mhz in the US. Shows up pretty strong on my sweep. Planning on building a stub filter to see if I can knock it down.

Cheers!
LitterBug


#5

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.

–bob


#6

Why not one of each? Knock the 930 down (open) and pass 1090 (shorted)…

Cheers!
LitterBug


#7

Forgot about those pesky things. Luckily I don’t live really close to those towers. I remember having issues with weak signal when I was looking at those with the RTL-SDR.