The 12VDC supply provides power for the camera and video modulator circuits. The video from the camera is fed into the video input of the modulator circuit. The modulated RF from the modulator is fed into a small antenna. Use of a dipole antenna that is resonant at the frequency of the modulator can extend the signal range. The RF travels across a short distance to the Sony Watchman TV receiver. A black and white image magically appears on the TV screen. The camera's video signal is connected to the video modulator with an RCA jumper cable. Power to the camera and video modulator is connected to the 12V power supply. Be careful with polarity, reversing the leads may damage the modulator. The camera that was used had reverse polarity protection built in.
The modulator's RF output signal is connected to a small antenna, the antenna can be made with two short lengths of #16 gauge solid wire. Alternately, for long distance wired operation, the RF signal can be fed into a length of 75 ohm coax cable with a 75 ohm terminating resistor across the far end of the cable. Connect the remote center conductor of the cable to the TV antenna through a 330 ohm resistor.
Turn the power for the camera and modulator on, turn on the TV. Tune the TV to the channel of the RF modulator, fine-tune the TV for the best picture. For full-time operation, use the appropriate AC adapter for the watchman. If battery operation is desired, run the TV from its internal batteries and use a 12V battery for powering the camera and modulator. A rechargeable lead acid battery with a series fuse (and a recharging circuit) is recommended.
A fun use for this system would be to create an engineer's view of a model train layout. A loop of wire near the track would make a good receiving antenna. Power could be pulled from the engine motor circuit using a bridge rectifier feeding into an electrolytic capacitor, just make sure not to exceed the camera's 12V maximum supply voltage.
Miniature black and white video camera, 12VDC, Model PC-206XP
Video modulator block, Jameco 141639CJ or equivalent
Sony Watchman miniature TV
12V DC power supply, beware of wall-warts - they often have inaccurate...