User's Manual

10-2 68P81093C75-A
Based on the comparison, a power control voltage is generated to
control the output power from the PA. This feedback and control
loop continually monitors the output power. It adjusts the control
voltage to maintain the proper output power from the PA.
Intermediate Power
Amplifier Module
Operation (800 MHz
stations only)
The 800 MHz PDR 3500 uses a custom, 50 Ω input and output,
variable-gain Intermediate Power Amplifier to boost the RF signal
from the Exciter Module to the final Power Amplifier Module. The
RF input to the IPA from the Exciter can vary from +13 to +16 dBm,
and the IPA is factory-tuned to provide an RF output of
approximately +21 dBm to the PA.
The IPA contains an RF amplifier IC, a voltage regulator and
potentiometer used to provide a control voltage to the IC, and
impedance-matching circuitry. A 3-wire cable carries +5V, ground,
and PTT signals from the backplane to the IPA. The IPA is mounted
on top of the Exciter bracket and is RF shielded.
Power Amplifier
Module Operation
The PDR 3500 uses the mid-power Spectra RF power amplifier (RF
PA) board, housed in a heavy-duty, shielded, aluminum heat sink.
The gain of the RF PA board is controlled by the power control
voltage from the Exciter Module.
The modulated RF signal from the Exciter or IPA (in 800 MHz
stations) is amplified by the RF PA and sent to the site transmit
antenna.
The transmit path inside the RF PA contains a directional coupler
(calibrated at setup), which feeds a DC voltage (proportional to the
output power) to the TX Power Control Circuitry in the Exciter
Module. This signal serves as the feedback signal in the power
control loop.
Receiver Circuitry
Introduction The Receiver Circuitry performs the following functions:
• Accepts receive RF signals from the site receive antenna
• Filters and dual conversion
• Outputs a digitized receive signal to the Station Control Module.
Receiver Module
Operation
The receive signal is generated from the site receive antenna to a
multi-pole, preselector filter which provides highly selective
bandpass filtering. In VHF and UHF stations, the preselector is
tunable and is mounted to the front of the main Receiver module. In
800 MHz stations, the preselector is fixed and is internal to the
Receiver.