wifi scanning affected by peripherals on MacBook -- why??

[lighting]

I use a 2015 MacBook Pro as if it was a desktop, with an external monitor and ethernet adapter on Thunderbolt and a USB hub with several USB devices, and an audio connection. With the external devices connected the wifi adapter only sees the strongest wifi access points in my vicinity. If I disconnect the peripheral connections I see many more wifi signals. This behavior is observed both on the utility Wifi Scanner and in what I see on the wifi system preferences page, so it seems like it's in the wifi adapter. It doesn't seem like the issue is any one peripheral — the effect is cumulative. Anyone else seen this? Any ideas on why or what can be done about it? It's a nuisance having to unplug everything to do a survey. Thanks!

 

[pete y testing]

a USB hub with several USB devices,

that will be your issue esp if its usb 3

 

[sfx2000]

Pete's right on the mark with USB3 - see it here with Macbook Air (2014 model) and MacBook Pro (Mid-2012 non-Retina).

Thunderbolt is fine, but USB3 does cause some interference, and if you look where the ports are on the right hand side, it's not very far away from the Airport card and antennas...