VisitPhone System 500 consists of
two handsets, each connected to a stainless steel two-gang wallplate via
stainless steel armored cable. Chrome plated handset hangers are attached
to the wallplate. Amplifiers are attached to the back of the wallplate
on the public (visitors') side of the visitation booth. The two phones
are connected by a short piece of three conductor cable, which is provided.
The system includes two cast aluminum, surface-mount, two-gang backboxes.
The phones may also be mounted to recessed concrete backboxes. In situations where the phones cannot be wall mounted, or counter mounting is desired the system may be ordered with separately mountable hangers. The handsets are provided with anti-tamper screws to prevent removal of the transmitter or receiver elements. The wallplates are also provided with anti-tamper screws. The handsets are fully hearing aid compatible. A volume control is available as an option.
The direct through-the-wall VisitPhone System 500 high output visitation phone pair is based on the principal of the voice powered telephone used for many years as battle telephones by the U.S. Navy.
In the VisitPhone System 500 the two voice (or sound) powered telephones, which utilize very efficient balanced armature magnetic elements are tightly coupled to low electrical drain solid state amplifiers (see block diagram below). The combination results in sound levels at the telephone receiver higher than those found in line connected telephones ... without the need for any electrical connections other than those between the two handsets in the vistation booth. The VisitPhone System 500 completely eliminates the need for remote power supplies, circuit cards and long conduit runs. A normal voice at the telephone transmitter will produce sufficient output at the opposite receiver to be clearly heard over an 85dB (A-scale) background. Because the amplifier drain is so low each VisitPhone System 500 pair will run on two flashlight batteries for over three years. Hook switches are not necessary, offering increased reliability.
The VisitPhone System 500 relies on the unique properties of the self-energizing voice powered telephone element. Unlike ordinary telephone elements which require an electrical current from a remote source to flow through them, voice powered elements produce their own current through conversion of the acoustic power of the speaker's voice, hence the term voice (or sound) power. Unlike the conventional electrically powered telephone, the tansmitter and receiver elements are identical and interchangeable. These highly engineered elements are coupled to very efficient solid state electronic components developed for low drain applications such as battery powered watches and hearing aids. The system is illustrated in the block diagram below:
The transmitter of one handset is
connected through an amplifier to the receiver of the opposite handset
and vice-versa. The outputs of both amplifiers are loosely coupled to