esp8266 wacky wifi

one way to get a screenshot....

This is rather weird. It all started when I got my old Nexus 7 tablet out of retirement. I'm doing some upgrades for the web server for the Raspberry Pi event coming up, and I wanted to use the Nexus to see if the web site would work on an Android powered browser. 

One of the applications on the Nexus is a WiFi analyser that I've used to pick and choose my WiFi channels. When I fired it up I noticed a few strange transmitters which were taking over the spectrum (as you can see above). 

I finally tracked this down to the esp8266 devices that I use in Hull Pixelbots. For some reason, when they wake up, they start doing things on WiFi channels. I've no idea of the precise meaning of this transmission, but I don't particularly like it. It turns out that if you turn off the WiFi before you do anything else (even turn it back on to connect to an access point) then you don't see this. 

I'd love comments from anyone else who've seen this, or has more knowledge of what is going on. In the meantime all my programs now start with:

WiFi.mode(WIFI_OFF);