Changes

== Rear Projection Television Receiver==

== Rear Projection Television Receiver==

A brief attempt was made to use the lens from a rear projection television to collect light and focus it onto the receiver. The screen of a rear projection television is a Fresnel lens [https://en.wikipedia.org/wiki/Fresnel_lens] that focuses light from a projector in the rear (essentially a single point) into a beam the size of the screen with little divergence, such that the TV’s image is visible to a person sitting in front of it. The team investigated the possibility of  using this lens in reverse, focusing all of the light incident on the screen into a single point in the rear where a receiver circuit would be placed. In order to confirm the focusing effect occurred as expected, the TV (with the projector removed) was taken outside on a sunny day and aimed at the Sun. Later inspection showed that sunlight was concentrated, not onto the projector’s former location, but instead onto a (now partially melted) section of the TV’s plastic housing. This test illustrated the difficulty of moving and aiming a structure the size of the television, a fairly serious constraint for portable test equipment. In addition, it was not clear that the team could successfully focus this particular lens into the point required. However, this type of lens - a Fresnel lens - was later used very successfully in [[System III]].

A brief attempt was made to use the lens from a rear projection television to collect light and focus it onto the receiver. The screen of a rear projection television is a Fresnel lens [https://en.wikipedia.org/wiki/Fresnel_lens] that focuses light from a projector in the rear (essentially a single point) into a beam the size of the screen with little divergence, such that the TV’s image is visible to a person sitting in front of it. The team investigated the possibility of  using this lens in reverse, focusing all of the light incident on the screen into a single point in the rear where a receiver circuit would be placed. In order to confirm the focusing effect occurred as expected, the TV (with the projector removed) was taken outside on a sunny day and aimed at the Sun. Later inspection showed that sunlight was concentrated, not onto the projector’s former location, but instead onto a (now partially melted) section of the TV’s plastic housing. This test illustrated the difficulty of moving and aiming a structure the size of the television, a fairly serious constraint for portable test equipment. In addition, it was not clear that the team could successfully focus this particular lens into the point required. However, this type of lens - a Fresnel lens - was later used very successfully in [[System III]].