Vocademy - Free Vocational Education Learn electronics technology for free at vocademy.net Solid-state Devices and Analog Circuits Day 6, Part 2 Practical Analog Circuits
Also Audio is mechanical with the Air being alternately being compacted and rarefied but RF Signals are Electromagnetic. So you could have overlapping Upper End AF with RF but a Dog wouldn't have a chance of hearing 20Khz RF Signal but could hear an Audio Signal of 20Khz.
I was thinking that myself. If everyone of us current subscribers, told other friends that love electronic tech...Bob would have alot more subscibers?!