In lecture, I've been using an expensive (\$2000) 10 GHz microwave demo setup consisting of a transmitter and a receiver. It can be used to demonstrate things like the transverse polarization of electromagnetic waves, and the difference in absorption between substances that contain molecular dipoles and those that don't. Can anyone suggest any ways of doing classroom experiments along these lines using super-cheap off-the-shelf equipment? Considering how ubiquitous radio is these days (wireless computer mice, etc.), it doesn't seem like it should be necessary to spend thousands of dollors to generate a low-power carrier wave and detect it. For example, it seems that you can get RFID readers for about \$50, and tags are extremely cheap -- but I don't know whether they can be used for these purposes. I had thought it might be fun to try to build a crude spark-gap transmitter, but it sounds like it's probably not possible to do so legally, since the signal is very broad-band and "dirty" (and the practical hobbyist setups built by history buffs actually seem like pretty complicated pieces of technology).

My understanding of the legalities is that for devices that fit certain parameters such as maximum power, there is something called a "class license" for a set of Industrial, Scientific and Medical (ISM) bands. This seems to cover a broad range of devices such as wifi routers, garage door openers, and so on.

• for more info on this contact me by message. -NN Oct 28, 2018 at 5:15

Almost any mobile radio aside from satellite links and anything in ISM band that are on the market uses linear polarization and applies a linear monopole where the ground is defined somehow by the body of the radio. But irrespective of all these you can make a dirt-cheap polarizer from a wood frame and parallel copper wires that are wound so that their spacing is $$< \lambda/2$$. The emission in ISM band is limited to $$<1W$$ which more than you ever need in a class-room size experiment.