Clear-Com Tempest 900 Reference Manual

8 Tempest®900 4-Channel Wireless Intercom System
Theory of Operaon
Tempest is a DSP (Digital Signal Processor) based, full duplex, wireless intercom system. It is a digital, point-to-point
communicaons system, operang in 26 MHz of spectrum in the 900MHz frequency band. This band allows users to
operate with no license requirements in most locaons.
The 900MHz band oers many benets. There are, however, a wide variety of technologies and users compeng for clear
spectrum in this limited band. Tempest ulizes patented and proprietary technologies to ensure a robust and reliable RF
link under a wide variety of physical and RF environments. This level of reliability is the most important aribute of any
wireless system.
Tempest ulizes proprietary, Frequency Hopping Spread Spectrum (FHSS) technology that has seven U.S. patents. Mulple
BeltStaon access is achieved by implemenng Time Domain Mulple Access (TDMA) with Frequency Shi Keying (FSK)
modulaon. Tempest uses an Algebraic Code - Excited Linear Predicon (A-CELP) voice compression algorithm to reduce the
bandwidth necessary for transmission and yet maintain the highest possible voice intelligibility. In addion, this algorithm
ulizes advanced lost packet masking technology, which greatly reduces the aect of packet loss, possible in all Digital RF
transmission schemes. The loss of audio packets is managed by the algorithm to reduce the possibility of detecng a loss
of audio.
The incorporaon of various diversity techniques provide an RF system that is robust and reliable under greatly varying
operaonal condions. Because of this inherent design, Tempest delivers superior operaonal range and greater levels of
interference and mul path fade rejecon. Covering extremely large areas or mulple coverage locaons can be problemac
with tradional wireless intercom systems. Tempest ulizes iSelect™ on-command roaming to allow users to move from
one area of coverage to another. iSelect allows Tempest users to easily choose the desired coverage area by selecng
the BaseStaon they want to communicate through. The BeltStaon (remote) remembers the last 64 BaseStaons with
which it has been Paired. When a dierent BaseStaon is selected, the hopping paern and key code of the BeltStaon is
synchronized to the selected BaseStaon and the BeltStaon logs into the BaseStaon.
Audio latency is a crical factor in all digital systems. The hop duraon in Tempest is intenonally kept very short - under
5ms. This short hop duraon limits the amount of data that may be lost in any one hop. More importantly, it reduces system
latency, which can cause undesirable echo. Total one-way (BeltStaon to BaseStaon) system latency is less than 50ms.
Even with this short system latency, unwanted and distracng echo will occur when interfacing with hard wired party-line
intercom systems unless echo-reducon technology is implemented. Echo is primarily the result of ineciencies in the
conversion of the two-wire signal. This condion exists in analog systems as well, but it does not cause unwanted echo

Clear-Com Tempest 900 Specifications

General

Brand	Clear-Com
Model	Tempest 900
Category	Intercom System
Language	English