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The On Site Paging (OSP) system consists of units designed for wall mounting, either individually or adjacent to each other. Fixed receivers and slave transmitters are housed in die-cast aluminum cases, while all other units use ABS plastic. Both case types offer protection against dust and mechanical damage, but units should not be placed in areas with moisture or extreme humidity. The operating temperature range is -25 to +55°C for radio equipment and 0 to +40°C for other modules. For optimal service, units should be in dry locations with moderate temperatures, avoiding strong electromagnetic fields, vibration, or rapid temperature changes.
Units communicate via serial transmission on a system bus. Adjacent units connect using ready-made modular system bus cables. Remote units, such as a Transmitter near an antenna, a PBX interface at a switchboard, or charging interfaces, use twisted-pair cables. If a bus cable is used, no other system bus connections are needed. Twisted-pair bus connections are made at screw terminals on the PC-board. The bus network must never form loops. All data buses are polarized. A maximum of 32 modules can be connected in a bus network. The maximum length for data buses is 3 km, and for the speech bus, it's 500 meters. Distances exceeding these limits require modems. Only twisted-pair cables, such as EKKX 4 x 2 x 0.5 or EKKX 10 x 2 x 0.5, should be used.
The A-bus and D-bus are used for data communication. The A-bus facilitates communication between modules, and the D-bus handles communication between the Central Unit and Terminal transmitters. Both carry constant communication, visible as a pulse train on an oscilloscope. The normal level is 8-10 Vp-p (A1 to A2, D1 to D2), dropping to at least 0.6 Vp-p with multiple units or long lines. The data buses are polarized. The four data buses (A, B, C, D) use balanced lines, adhering to EIA standard RS-485 and CCITT recommendations V.11 and X.27. A- and B-buses are identical and connect interface modules. The C-bus is for communication between different installations (e.g., two Central Units). The D-bus transmits pagings from the Central Unit to Terminal Transmitters.
The SP-bus is a two-way line connecting all modules that handle speech signals. It is transformer-coupled, with a signal level of about 2 Vp-p between SP1 and SP2 during speech. The FL-bus is a one-way speech bus for terminal transmitters in frequency-locked systems, driven by a low impedance driver and is polarized.
Maximum total wiring lengths are:
For extended wiring lengths: If data bus lengths (A, B, C, D) exceed 3000 m or if more than 32 units are on a bus, the signal must be amplified. A Bus Converter T938BC2 is used for private lines, and a Data Modem T938D for leased lines or very long private lines. If SP-bus or R-line lengths exceed 500 m or 1000 m respectively, a Bus Amplifier T938BA is used for 1-way speech on private lines, and a Speech Modem T938S for 2-way speech on leased lines. If the FL-bus exceeds 3000 m, a Bus Amplifier is used.
A telephone set or PBX can serve as a control unit via a PBX Interface module. The PBX Interface accepts dialing pulses and DTMF tones, connecting to trunk or extension lines. It communicates with other OSP modules via the A-bus and, if speech is desired, the SP-bus. Additional PBX hardware/software may be needed for full paging system functionality.
There are two types of transmitters: Terminal and Slave. Terminal transmitters are controlled by the Central Unit and receive pagings on the D-bus. Slave transmitters extend coverage, connected via coaxial cable from the driving transmitter. The D-bus is electrically identical to the A-bus, supporting up to 32 units with twisted-pair wiring up to 3 km. If speech is used, the SP-bus must connect to terminal transmitters. The SP-bus length without a modem must not exceed 500 meters; with a 1-way SP-bus and T938BA bus amplifier, it can extend to 3 km.
In HF installations, a Power Divider is needed between every transmitter to drive Slave Transmitters. In UHF systems, a Slave Driver is used between the Terminal Transmitter and the first Slave Transmitter in series. Slave transmitters have one output and can be connected in series or used as line amplifiers. Connecting an antenna to the line amplifier is advisable, especially in speech systems where speech quality depends on coverage. Slave transmitters connect with RG-8 or RG-213 coaxial cable, up to 700 meters. Longer distances require line amplifiers. Slave transmitters are fed by a separate power supply, but if mounted near other units, power can be shared. Equipment for Slave Transmitters includes:
The Slave Driver U952DR has one antenna output and two outputs for driving Slave Transmitters from a UHF Terminal Transmitter, U952T. It also ensures a proper level at the Slave Transmitter input and operates in the 53-65 MHz band to reduce coaxial cable losses.
Frequency Locked Transmitters: A Reference Module, containing a stable reference tone generator, is placed near the Central Unit. Each transmitter has a combined SM/FL (Speech/Frequency Lock) T952SM/FL module, which uses the reference tone to correct carrier frequency. A Slave Driver is needed if the Terminal transmitter drives Slave transmitters. Equipment for frequency locking:
Without Modem to Transmitters: Transmitters connect to the D-bus and FL-bus. If the FL-bus maximum length is exceeded, the transmitter's speech bus must connect to the FL-bus on the Reference Module or Bus Amplifier. Multiple transmitters can connect to the D-bus if the 3 km total length is not exceeded. Each Reference Module and Bus Amplifier has two FL-bus outputs. The D- and SP/FL-buses must be correctly polarized.
With Modem to Transmitters: Data and Speech modems introduce delay, causing distortion in overlapping coverage areas. Signals to transmitters should be delayed equally. The Central Unit generates the transmitter code on the D-bus. The same number of modem-pairs must be used between the Central Unit and each Terminal transmitter. Multiple Terminal transmitters can connect to one Data modem if suitable. Data modems for the D-bus must be synchronized. Speech signals can come from PBX Interface, Receiver Interface, or Control Keyboard. If speech modems are used, a modem compensator must be used at terminal sites where speech is fed locally. The Modem Compensator delays local speech by an amount equivalent to the delay from a speech modem-pair with up to 3 km cabling. Its output, DFL ("Delayed Frequency Lock"), has the same electrical characteristics as the FL-bus and can be amplified by the Bus Amplifier. DFL connects to the speech bus in the Terminal Transmitter. Multiple modem compensators can be connected in series.
Receivers: Talk-back Receivers connect to a RI (Receiver Interface), which connects to the A- and SP-buses. Up to four receivers can connect to one RI, each with a separate twisted-pair not exceeding 1 km. If the distance exceeds 1 km, move the RI closer or use modems to extend the A-, B-, and SP-buses. The twisted-pair (R-line) between each receiver and its interface is separate from the system modular bus, even when units are mounted together. When the Receiver is not activated, this line carries a quality tone of about 2.4 Vp-p (between L1 and L2). When activated, the signal is a combination of speech, data, subtone, and quality tone. The line is not polarized.
Antennas: Various antennas (ground-plane, dipole, helix) are used, chosen based on the site. Dipoles must be ordered for the correct frequency. 900-system antennas can be grounded, but large potential differences between ground points should be avoided. An outdoor antenna should be centrally located and unobstructed. Avoid metal-clad chimneys. Three location alternatives:
UHF Antennas: UHF transmitters in the 900 system use a CXL-70, a broad band half-wave coaxial antenna for 406-470 MHz. It is dc-short-circuited and has an "N" type connector. The CXL-70 is mounted at the top of an antenna mast or with a supporting boom (at least 0.5 m). It is designed to be insulated from the mast but comes with a nut and washer for dc-connecting the antenna ground to the mast (normally not used). For talk-back, UHF/VHF, or UHF/UHF systems, a common base antenna with duplex filters can simplify installation.
HF Antennas: HF installations can use:
Tuning Circuits and Power Divider: The MFJ-901B antenna tuning unit for HF connects between the transmitter and antenna. It matches transmitter impedance to the antenna if installation is difficult or coaxial cable has high SWR. The Antenna transformer MAT-50 is used in HF installations at the transmitter output for galvanic isolation and protection from over-voltage/lightning transients. The Power divider MPT-50 in HF installations divides output power: 20% to the next slave transmitter and 80% to the antenna, or to two antennas. Its outputs are galvanically isolated from the input, so an MAT-50 is not needed when MPT-50 is used.
Antenna Cables: Coax cables (RG-8 or RG-213) between transmitter/receiver and antenna should be as short as possible. Attenuation is about 0.8 dB/10m at VHF and 1.5 dB/10m at UHF (6 dB attenuation reduces coverage by 50%).
Power Supply: All units use 12.5 V DC. They can be powered separately, but typically a common power supply feeds units in one location. The power supply connects to screw terminals on one unit and then in series to others. Wiring from the power supply must limit voltage drop to modules to 0.5 V at max load. If total loading exceeds supply capacity, an additional power supply is needed.
Current Consumption (max load in Amperes):
Addressing: All units on the system bus need a unique address for communication, set with an address switch before power is applied. The address is read and stored at start-up. The function indicator (LED) blinks at 8 Hz initially, then lights continually after max 90 seconds, indicating communication with the central unit. The address consists of two hexadecimal digits from the eight sections of the address switch: sections 5-8 for the first (most significant) digit, and sections 1-4 for the second digit. This allows 256 possible addresses. The Central Unit always has address 00. Other modules are addressed in ascending sequence. Each address must be unique regardless of the bus connection. Transmitters in non-speech systems must have hex 0 as the first digit unless sequential transmission is used. In speech systems, transmitters must be in the hex address range 80-FF. An address register should be kept for each installation. When using sequential transmission, the sequence number is set by sections 5-8 of the address switch. The central transmitter transmits in sequence 0 (address 00), and transmitters meant to transmit simultaneously also have hex 0 as the first digit. Subsequent sequences use hex 1, and so on, allowing up to 16 transmitters per sequence. Sequential transmission avoids interference but cannot be used in speech systems.
System Check: After installation, a functional check is performed according to each unit's installation guide. Initiate a paging to confirm pocket receiver response. Repeat for all units that generate pagings, including pocket transceivers. In speech systems, verify voice message clarity. Check other functions like absent indication, busy tone, and mobile-to-mobile calls. Note: Battery saving time (set in PUP or PDM) must be 0.5, 2, or 5 seconds. Mode 0 seconds is for testing only and not supported by the system, as it decreases handset performance and battery life. Messages and alarms from the system to the handset must be transmitted with at least one repetition for reliability. If a malfunction occurs, check LEDs:
Combined Systems: In combined 800/900 systems, the T840IU interconnection module is installed in the T840 central unit and connected to the OSP system bus via twisted-pair wiring (A and possibly SP-buses). Charging racks can be used separately or connected to a T966CI charging interface for high current charging and/or absent indication. Racks and interfaces connect via a ready-made 12-conductor cable, with a maximum distance of 1.5 m. Each charging interface has connections for four charging racks. The charging interface connects to the A-bus if absent indication is desired. An essential difference between old 800 systems and OSP systems is that 800 systems must be grounded at only one point if units are dc coupled. This must be considered in combined system planning. If both transmitters are on grounded masts, ground currents can cause interference between T840LM and T850. Solutions: install antenna transformer MAT-50 on transmitter T850, or install modem T838 between T840LM and T850.
General| Brand | ASCOM |
|---|---|
| Model | telePROTECT 900 |
| Category | Security System |
| Language | English |
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