Canon uses the 2.4 Ghz band for their wireless flash system, the nearest cellular ranges are at 2.3 and 2.5 Ghz and those aren't in heavy/common use in the U.S.
But 2.4 Ghz is very heavily used for a variety of purposes including the most popular WiFi range, security systems, baby and other monitors, remote sensing (temperature, general weather, etc.). And the fastest growing and most common interfering device in this range is the ubiquitous Bluetooth system. So the Canon wireless flash system is in a VERY busy neighborhood.
Link loss/link low reliability can occur both from direct interference on exactly the same frequency (which is why most devices can automatically or manually channel hop to find a suitable spot) AND from general loss of device sensitivity due to a noisy RF environment. I suspect the latter is the problem with Canon devices and they aren't robust against a high level RF environment; this can occur due to poor quality on the receiving side and minimal power/poor antenna on the transmitting side.
Nothing is fully immune to this sort of interference but devices that transmit at the allowed limit with an efficient radiator combined with receivers that have a high dynamic range and steep rejection of just off frequency interference will be most reliable in terms of maintaining a link and minimizing packet errors.
A spectrum analyzer isn't an instrument photographers carry around but it will tell the tale of interfering signatures in an RF environment 🙂 I have used my Tektronix 7854 scope with 7L12 spectrum analyzer plug in for a lot of applications but so far NOT for finding flash interference. But if you look at the 2.4 Ghz range in a typical public spot, the analyzer is going to show a lot of activity.
And although MOST of the "garbage" from power supplies stays below the 2.4 Ghz range, some devices are so noisy that these unintentional radiators create problems. The power supply in some LED bulbs is so noisy that using one in a garage door opener will interrupt communications with the controller (400 Mhz range for these devices) preventing the car remote from closing the door while the light is on after exiting the garage. The power supplies used with home entertainment devices, digital devices, and home appliances are often far worse, particularly replacement units that don't even pretend to meet U.S./EU RFI regulations.
Rodger
