Heliograph

0:0:0 A heliograph is a wireless telegraph that uses reflected sunlight to transmit code. Though resembling a similar device called a heliotrope, Henry Christopher Mance is acknowledged as having developed the heliograph for the British. Heliographs were used during the late 19th and early 20th century, before being superseded by radio.

A primary mirror is oriented towards the receiver using an aiming rod when the sun is ahead of the sender. A secondary mirror allowed for sunlight from behind the sender to be used. Tilting the mirror or activating a shutter allows the sender to vary the signal, such as creating the pulse patterns used by Morse Code. The beam has excellent range in bright sunlight, visible up to 125 miles away.

Though its use was difficult to detect, agents close to the beam's path could potentially intercept messages. The beam could be modified by using tubes to limit its dispersion (against man-in-the-middle attack), or lenses to widen its dispersion to improve visibility to moving receivers.

Battlefield 1
The Heliograph is a gadget made available to the Infiltrator Elite Kit in Battlefield 1: Turning Tides.

Acting as a spawn beacon, it allows teammates to spawn at its location. As no similar gadgets are available in Battlefield 1, its placement is announced to the player's team.

The heliograph can be resupplied, allowing the Infiltrator to place a new spawn point (replacing the old one).