User Manual

SECTION 1: THEORY OF OPERATION
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The receiver injection synthesizer creates the injection signals used by the three (3) internal FM receivers.
The receiver injection frequency is 45 MHz below the base station’s receive frequency.
The VHF signal from the VCO is applied to amplifier for amplification and load isolation and is then routed
to a 4-way divider network. The divider network splits the injection signal into four (4) equal amplitude
signals. Three (3) of these signals are used as injection signals for the three (3) receivers; the fourth
signal is sent back to the synthesizer as feedback for the PLL.
The feedback signal is used by the digital frequency synthesizer to keep the radio on channel.
The frequency synthesizer divides the injection signal to produce a quotient signal of 12.5 kHz . The
synthesizer also divides the signal from the 10.0 MHz reference oscillator to produce a 12.5 kHz signal.
The synthesizer compares the phase of these two (2) signals and outputs a signal (PD OUT) proportional
to their phase difference. A passive loop filter converts the PD OUT signal to a DC control voltage that
locks the VCO on channel.
In this manner, the VCO is compared to - and forced to emulate - the high-stability reference oscillator.
This configuration is commonly referred to as a digital Phase-Locked-Loop (PLL) frequency synthesizer.
VHF Receiver
The IP1B employs three (3) independent, high-performance, low-noise, dual conversion FM receivers.
The receiver is divided into two (2) main sections, a front-end section and a 45 MHz receiver section.
VHF Front-End Section
Functional block diagram of the receiver front-end section.
The front-end section employs an advanced-architecture, cascaded-LNA (low noise amplifier) design for
extreme sensitivity and high-overload performance.
Receiver input signals are first filtered by a pre-selector band-pass filter and are then routed to a LNA.
The amplified signal is routed through another band-pass filter.