Remember those stupid "Get TV reception from the powerline" adaptors?
 

Rememer the ads in "TV Guide" for devices that claimed to use the power wiring of your house as a TV antenna for TV reception? They were usually a plug in plastic cube with a plastic cylindar on top, and had twin lead coming out of it to connect to the TV's antenna terminals. At best they may have had a capacitor coupling to the powerline. Some had no connection at all; it just had the twinlead stub stuck into the plastic cylindar. These were likely intended for city people living in apartments not far from the TV transmitters. Where even a wet noodle would work...

At first the wall wart in the picture looks like a modern version, with the F connector on the side of it. But it's not. It's just a 12VDC 150ma wall wart. Who knows why they selected an F connector for the output jack. :-)

I used to work at a rat shack. Being told to push junk like this is why I quit.

I had a little Sylvania Hospital set from the late 70's that fed the power in through the antenna coax connector. Took me a while to figure out why there was no place for a power cord!

This device is likely a power supply for an in-line amplifier....you would feed the 12 vdc up the antenna coax to the amplifier mounted at the antenna and then use a blocking capacitor at the set to keep the DC out of the TV set.

Isn't this kinda stuff like, uhhh, "dangerous" ?!? -Sandy G.

These could be dangerous if the coupling capacitor to the line became leaky or shorted.I have one of these things that claims to replace an AM radio antenna.It looks to be from the 1930's.

Many FM clock and table radios use a capacitor connecting the powerline and FM antenna input to provide an antenna. The capacitance is in the pf range so that there is no appreciable 60 hz ac coupling. Sometimes a capacitor is created in this setup by winding the antenna wire around the power cord, or a metal sleeve that slips over the cord.
Winding about 6" of wire connected to antenna terminal around the power cord insulation should provide the same effect as the plug-in antenna gadget.

I've got an old solid state RCA Victor wooden table top AM/FM radio with a metal sleeve on the power cord, similar to what Chad mentions. Except this is external and I can disconnect it from the antenna terminal. It works fine only if the signal is strong.
I also have some old B&W portable TVs that have the same setup for the built in UHF antenna. There is no direct connection to the AC power line, just like the RCA radio.

yes.
i had a cheap 9v battery eliminater that was a resister,diode,filter cap,and zener.
had a non polarised plug.
50/50 shot at the - side being the ac hot.
grab your transtistor radio and touch earth ground and ZAP!!!!