Third, the control signals form the Modulation Encoder are used
to switch individual RF amplifiers ON or OFF. The individual
RF amplifier module outputs are combined in the RF combiner.
The RF output of the Power Amplifier stage changes in very
small steps, or discrete quantities, and is passed through the
bandpass filter to smooth the step transitions.
4.9.6.1
Digital Modulator Characteristics
The patented Harris Digital Modulator uses new technology
which produces a very high quality, low distortion amplitude
modulated signal for AM broadcasters.
Overall AC to RF efficiency of the DX-25U is very high, because
the digital modulator uses very little power and the RF amplifi-
ers are high efficiency, solid-state, Class D switching amplifiers.
The transmitter has little or no overshoot or tilt with square wave
modulation, even at very low audio frequencies and the modu-
lation envelope accurately reproduces the audio input signal.
Section IV - Overall System Theory
Rev. AA: 8-9-00
888-2297-002
4-11
WARNING: Disconnect primary power prior to servicing.
