I had read an article about a large microwave cavity but cannot find the dimensions of the room, it isn't available online.

Lewin, says his former student, figured out that MIT's biggest lecture hall, the cavernous Room 26-100, could be turned into a low-energy microwave cavity. "He mounted a light bulb on an antenna," recalls Leeb, "and he'd walk around mapping the microwave field according to where the light bulb would glow or dim. It was terrific."

http://web.mit.edu/giving/spectrum/spring02/hands-on-learning.html

 

I want to calculate the approximate frequency generated by the cavity and wonder if anyone has the dimensions for Room 26-100?

 

I have heard that amateur radio "microwave" enthusiasts have sometimes turned metal silos into microwave cavities. Microwave is sort of a misnomer as the MIT room cavity could be in the low high frequency range. Does anybody know of other examples of "large" microwave cavities?

nope!

 

anything that size (even a small toilet) would be in the HF --> VHF band.

 

MW`s work in CMs at Fullwave antenna, anything in Metres and at best you`re looking at signal diminishing and a whole host of 2`nd 3`rd or more harmonics (

 

Either your description is lacking detail and there`s a bit more to it than that, or it`s Bogus

In cavity oscillations, one normally refers to modes not harmonics.