User Manual

Vytek PTX-150
Doc Ref : 7M393-1 Version C1 Page : 1
 VYTEK - 2000
1. INTRODUCTION
INTRODUCTION
1.1 GENERAL
The VYTEK PTX-150 Paging transmitter is a state of the art DSP/DDS (Digital Signal
Processor/Direct Digital Synthesis) based device capable of generating all paging
modulation formats, and is designed as a general purpose transmitter for all speed paging
systems.
Construction of the transmitter is fully modular. Internally, the case is divided into
compartments with PCB’s arranged in modules, all interconnected by plug/sockets. All
modules can be replaced without the use of a soldering iron. Replacement modules do not
require alignment or tuning.
The VYTEK PTX-150 transmitter incorporates a universal AC supply and can also
operate from a single DC supply for battery back up operation. Software permits the
option of ”Hot standby” with auto changeover initiated by software selectable fault
conditions.
The VYTEK PTX-150 transmitter is designed for 100% duty cycle at up to 55°C ambient
conditions and utilizes advanced cooling technology to maintain very low power
transistor junction temperatures. This approach means assures ultra reliable power
amplifier performance.
The power amplifier temperature is monitored and if the temperature rises above a preset
amount (35°C), the diagnostics system is alerted and the fan and cooling system is
activated. The transmitter is protected by over temperature feedback control to the PA
drive input and also incorporates auto fold back for high VSWR conditions.
An external frequency reference input is designed to handle standard reference sources
and will lock the transmitter to the external reference. An internal ±1 PPM TCXO
(Temperature Compensated Crystal Oscillator) is provided as standard if no external
reference is available.
In POCSAG wide area systems, the carrier can be ”dithered” by what is known as a
”Black noise” algorithm, to minimize cancellation of equal amplitude carriers from
adjacent transmitters. This technique has been used for at least 12 years and is superior to
the Carrier offset method. High stability carriers are unnecessary for the carrier dithering
technique. For high-speed ERMES and FLEX systems, the carrier can be offset in 1Hz
steps.