I used the search term "5W Stereo PLL Digital FM Transmitter
" on e b a y and found that these are no-name black box units advertised with the punch line "Build your own FM stereo radio station!
" so I would think that there is a certain element of the population who might use such a device for unauthorized broadcasting. The input is via a standard male-male audio cable as used in headphone jacks of consumer audio players like the iPod.
The photos of the box itself show no FCC/IC stickers or UL/CSA/CE approvals, although the bottom is not pictured, but I wouldn't hold my breath expecting to see them there.
The only sticker is a Chinese manufacturer's inspection label. Only the external power supply has approvals since it is a commonly sourced model not from this manufacturer.
The recommended antenna for this unit was found by using the search term "GP antenna
" on e b a y, which provided a link to a "1/4 wave Professional GP Antenna BNC or NJ 26ft.cable" with specifications provided.
Anyone want to take a rough guess at what the radiated power calculation of this transmitter/antenna combination might be, and a guess at what it's propagation might be from, say, a height of 20 feet?