Technical Manual

380-520 MHz Power Amplifier
Appendix A - UHF Circuit Descriptions
A-
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ATLAS 4500 Multimode Station Technical Manual July 2021
This module is a high linearity low intermodulation 75-Ω power driver with
approximately24 dB gain, 28 dBm RF power. It operates at 24 V at 450 ma.
A.3.2.4 Output Power Amp
The PA output power amp stage uses a high performance power FET in a Gemini
package. This is mounted on a copper heat spreader plate, on a fan-cooled
aluminium heat sink.
The input matching uses a 90° section 17-Ω transmission line balun loaded with
ferrite to prevent oscillations. Then, a balanced matching section gives
approximately 0.5-Ω Zin FET.
Input series resistors and a parallel resistor are used to prevent instability.
The output match from approximately 6 Ω Zout consists of a 2-section match, then
to a 90° section 17-Ω transmission line balun to give 50-Ω feed.
Due to use of open long balun there is high Q resonance for second harmonics at
one frequency area. A power absorber network for approximately900 MHz reduces
amplitude of second harmonics on FET drains and gives better intermodulation of
the PA.
A.3.2.5 Power Coupler
The PA feeds an output RF coupler port, providing about 3 dBm at 100 W output.
This is for DPD use, and is fed to the Exciter.