Source: http://gizmodo.com/8k-yes-8k-broadcasts-just-took-a-major-step-forward-1505680131
Back in May of 2012 the NHK's science & Technology Research Lab in Japan successfully broadcasted an 8K, 7680x4320 signal over a distance of 2.7 miles using UHF frequencies. As a proof of concept it showed that 8K TV could be successfully delivered to televisions over the air, but it lacked the distance of traditional TV broadcasts.