AMX TXC16 Plus Specifications download pdf (Page 181)

SG-2000 MANUAL 174

The SGC Building, 13737 S.E. 26th St. Bellevue, WA. 98005 USA

23.2. LPA Testing Procedures

This section details the procedures for testing the LPA PCB of the SG-2000

radio.

23.2.1 Required Testing Equipment

Working LPA sample

12 inch/lbs calibrated torque wrench

RF Signal Generator with capability of +3 dBm 1.6-30 MHz RF out

Power Supply Capable of at least 30 Amps at 13.6 Volts (PS-35)

Connection Cables

Spectrum Analyzer

Tracking Generator

Multimeter

50 ? 200 W Dummy Load Antenna 30 dB attenuator

Watt Meter and 250 W slug

SGC LPA Test Box, SGC-Twin Current Meter

Variable Power Supply 5-40 V, > or = 2A

23.2.2. Circuit description

The LPA (linear power amplifier) has two pages to the schematic, J30100500.

Transmit RF is received from the exciter on connector J1. The signal is

amplified by Q1. Transformer T2 splits the signal for the Class "B" amplifier

containing transistors Q2 and Q3. The signal is combined and then split again

for the dual Class "B" final amplifier containing transistors Q6, Q7, Q10 and

Q11. The signal is recombined and sent to the filter section. Note: the final

amplifiers get power directly from the power supply. The filter section is

controlled by IC3 and IC4. There are six low pass elliptical filters which are

selected based on the transmit and receive frequencies. Relay K1 switches the

filters between the transmit and receive paths.

The forward and reverse RF power is detected by transformers T13 and T14.

The signals are rectified. The rectified signals are used for the ALC (automatic

level control), VSWR shutdown and the analog to digital converter, IC5. The

digitized signals are sent to the exciter where they are eventually used to drive

the VSWR and FWD meter on the display.

The SG-2000 has protection from over and reverse voltages as well as transient

spikes. The voltage protection circuit uses a normally open relay which is only

closed when the proper voltage is applied. Diode D1 prevents current from

flowing during reverse polarity conditions. Transistors Q19, Q20 and Q21 form

a logic switch. Diode D11 sets the level of the logic switch. During normal

operation, transistor Q20 is on and Q19 and Q21 are off. Current flows through

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AMX TXC16 Plus Specifications Page 181