Technical Manual Technical Description
© SPECTRA ENGINEERING 2006 Revision 4.2.3
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4.3 Power Amplifier Module
The MX800 now supports Spectra Engineering new full switching bandwidth
Power Amplifier Module (Wide Band PA). Which requires no tuning, equals,
exceeds or covers several of Spectra’s band allocations, (refer to section 7.4
for details of the band allocations). This new generation Power Amplifier
features much wider RF Bandwidth, higher efficiency, greater stability out of
band and to zero power levels.
This PA is now being rolled out as the standard production PA.
Please see superseded technical section 8.1.1 for older hybrid type PA.
Wide Band PA (50 Watt Model)
RF from the Exciter passes via a coaxial cable to the input of the PA Module
and is first attenuated by a 50 ohm pad, which is used to provide a good
50 ohm source impedance for the first LDMOS driver amplifier. The RF is
amplified to around 5 Watts at the driver output, and is band dependant.
Note: this point does not have 50-ohm impedance and the drive power cannot
be measured directly with a 50 ohm Wattmeter. The signal from the driver is
then matched by a broadband network to drive the low input impedance
associated with the final transmit LDMOS power amplifier transistor. The
transistor's low Drain impedance is then also matched back to 50 ohms by a
broadband matching network covering a very wide bandwidth. Prior to
transmission, a low loss 13 element elliptical low pass filter, filters out the
unwanted harmonics to less than –90 dBc.
A dual directional coupler consists of coupled microstrip transmission lines
fabricated on the PCB artwork. The sampled RF energy is rectified to provide
a proportional DC voltage output.
The PTT signal enables the amplifier circuit by providing bias to the
transistors. A thermistor TS1, physically located on the PA heatsink monitors
the heatsink’s temperature and is monitored by the Micro Controller.
4.4 Micro Controller Board
Refer:
Block Diagram BD003 (Rev A to H)
BD005 (Rev I upwards)
Circuit Diagram CS001-1/6
The MX800 Micro Controller Board has 4 main functions
Overall radio management
TX and RX signal processing
RF power control
User interface
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