Specifications

Table Of Contents
MAINTENANCE
Page 123 MRC-565 Packet Data Radio Operations & Maintenance
6.2.6.4 5 V Regulator
A linear Voltage Regular is used to regulate the 5.3 voltage to 5.0 volts for powering the CF
ADC, The DSP DAC, and the USB On-the-Go circuit.
6.3 Power Amplifier (MRC-56500301-10)
The amplification of the +0 DBM output of the CMU to the final RF output of 10, 25, 50 or100
watts is accomplished with 3 RF stages, A1, A2 and A3. The PCB mounts to the aluminum
chassis that forms the bottom half of the MRC-565 enclosure. The chassis also provides a heat
sink for all the high power RF transistors.
The RF output of the CMU (0dBm) is amplified to 50 milli-watts (17dBm)by the first stage of
the amplifier, A1. The second stage of the amplifier, A2, amplifies the signal to 2 watts
(33dBm). The final stage of the amplifier, A3, which includes two MOSFET Transistors and two
center tap transformers, amplifies the signal to 10, 25, 50 or 100 watts depending on level set by
operator. Frequency range for this amplifier is 40-46 Mhz.
A unique power switch circuit is used to control the application of DC Power (+12VDC) to the
various amplifier stages. The purpose of this control is to insure that the RF power output is
switched on with a controlled rise and fall time (approximately 1 msec) when the TXKEY signal
from the processor is turned on and off.
The TXKEY signal from the processor triggers a duty cycle limit. When the key is held on in
excess of one second or when the duty cycle exceeds 10%, the TXKEY will be gated off.
A temperature sensor is located on this PA to allow the processor to read the internal
temperature of the unit. This temperature can be displayed on the operator port, or it can be
transmitted to a distant MRC MRC-565
The final section of the power amplifier assemble contains a pin diode T/R switch, a 5
th
order
elliptic low pass filter, a directional coupler, and a BPF on the Receiver port of the T/R switch.
The T/R switch, low pass filter, and directional coupler are enclosed in a metal shield.
An ALC loop is used to maintain a fixed RF output over temperature and voltage variations.
The output of the power amplifier is coupled through the T/R switch to the harmonic low pass
filter. The switch is implemented with PIN diodes.
A fifth order elliptic low pass filter reduces the harmonics of the output signal. This enables the
amplifier to meet FCC requirements for harmonic emissions. The filter attenuates second and
high order harmonics by 60 dB. Its insertion loss is less than .3 dB.