TMA2Q/LPC2Q Tower Mounted Amplifier Instruction Manual
Refer to last page for revision and copyright information, File: TMA2QInstructionManual.doc, Page 12
IV. Circuit Description
A. Introduction
The TMA2Q and LPC2Q operate as a pair. The frequency range 50...500 MHz is limited by the quadrature
coupler. The amplifiers and bias-tees are rated to 3 GHz. All RF components are shielded, state-of-the-art
modular devices. The power supplies use discrete passive components and low dropout linear voltage regulator
integrated circuits. The LDO regulators not only provide a voltage regulating function but also heavily filter any
noise on their inputs.
B. TMA2Q Tower-Mounted Amplifier Assembly
The TMA2Q components are enclosed in a weatherproof polyester enclosure. The layout is shown in figure 7,
and a schematic is shown in figure 8. The TMA2Q uses the Mini-Circuits ZX60-33LN+ low noise amplifier (LNA)
module and Mini-Circuits ZFBT-282-1.5A+ bias-tee power coupler modules. The low noise amplifier module
provides a nominal 20 dB gain and has a nominal 1.0 dB noise figure. However, implementation losses and the
quadrature coupler in the LPC2Q increase the system noise figure by as much as 4 dB.
On each transmission circuit, a lightning arrestor assembly with a type-N coaxial connector couples the antenna
to the low noise amplifier module through an adapter while protecting the input. The RF input port of the
amplifier module is connected directly to the arrestor and its output is connected to the bias-tee power coupler
through a power/voltage limiter. The limiter prevents momentary surge voltages on the bias-tee RF port from
damaging the amplifier. The RF + dc port of each bias-tee connects directly to a type-N coaxial connector, which
carries amplified RF back to the LPC2Q and dc from the LPC2Q to the TMA2Q. The dc output port on each bias-
tee in the TMA2Q is connected to a regulated power supply, which supplies 3.3 Vdc to its corresponding
amplifier module. The design voltage input range to the power supply is 6.3 to 8.0 Vdc.
