SECTION 3: DESCRIPTION AND STATION BLOCK DIAGRAM
The Exciter Module generates the modulated rf paging signal at the desired transmit frequency. This signal is then sent to the Power Amplifier Module.
The reference modulator receives a 16.8 MHz reference signal from the NAC Board. The reference signal is modulated by the reference modulation (REF MOD) signal. The resultant modulated reference signal is sent to the Synthesizer.
The Synthesizer compares the modulated reference signal with a feedback sample of the VCO output. Depending on whether the feedback signal is higher or lower in frequency than the modulated reference, correction pulses are gener¬ated. These pulses are then fed to a charge pump which outputs a dc control voltage.
The dc control voltage from the synthesizer is fed to the VCO. The VCO also receives an audio/data modulation signal (VCO MOD) from the Station Control Board that modulates the VCO to produce a modulated low-level rf carrier signal. This signal is fed through impedance matching, amplification, and filtering and is sent to the RF Switch Circuit¬ry, and then output to the Power Amplifier Module.
There are two VHF Exciter Modules: 132-154 MHz and 150—174 MHz.
The 280 MHz Exciter Module covers the range from 276-284 MHz.
The UHF Range 2 Exciter Module covers the range from 438—470 MHz.
The 900 MHz Exciter Module covers the range from 928-944 MHz.