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Even if the antenna weren't noticed, radio direction finding is, in fact, a thing - and at 900 MHz, it's a pretty easy thing. Frankly, I am only really disappointed the talk was pulled because I was planning to attend to ask the presenter some very pointed questions about why he thought putting wifi comms across a 900MHz backhaul was innovative or interesting at all - much less why he was fiddling about adding a raspberry pi to the mix.