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3-1
Exciter Section
The exciter section is composed of DM-3100AB Exciter and Exciter switch. In the case
of single transmitter exciter switch is not applied.
3-1-1
DM-3100AB Exciter
Principal features of the DM-3100AB Exciter are summarized below.
(1) Digitalized modulation and linear and non-linear correction
The visual VSB modulation, the white clip, the aural FM modulation and the linear
and non-linear correction are executed at the digital base band. Non-linear distortion
caused by PA and linear distortion are corrected automatically by using internal test
signal and feedback signal from TX output. Also these distortions can be corrected by
manually.
(2) Direct quadrature modulation and AGC
The digital I/Q signals are converted to analogue, then converted to RF directly by the
quadrature modulation circuit.
AGC is done at RF stage. The AGC circuit for visual is of the pedestal type, operating
to hold the pedestal or black level constant. If there is no modulation present, the AGC
is automatically switched OFF. The AGC circuit for aural is of the average power
type. The gain variation that can be controlled by AGC is restricted to approximately
±1dB.
(3) Synthesizer
The synthesizer incorporates voltage-controlled crystal oscillators (VCXO) with the
local frequencies. This frequency is locked to a 10MHz reference frequency.
The 10MHz reference frequency is available from the crystal oscillator incorporated in
the exciter and high frequency accuracy may be achieved by the use of an external
reference frequency from a rubidium oscillator or GPS receiver. This permits high
frequency precision, assuring high short-term stability and reduction of SSB noise.
3 - 2
GWP-G22906
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