Theory of operation
AUDIO LIMITER
Audio signals are supplied from 2 XLR balanced connectors – Left and right which being converted from balanced to unbalanced by low noise operational
the limiter function.
STEREO ENCODER
The stereo encoder is based on a microcontroller and a high performance analog switch, the 19Khz pilot is generated with a D/A technology by the
microcontroller (DSP), this technology produce a much improved spectral clearness and reduce the harmonic compared to other pilot generation methods, By
which also improve overall performance of the MPX signal.
RF SECTION
The base of the RF section is a VCO (voltage controlled oscillator), a VCO produce a frequency corresponding to an input voltage, mixing the audio with the
control voltage will generate FM signal (Frequency Modulation).
To Stabilize the VCO frequency, a Phase Lock Loop circuit (PLL) is being used.
The PLL compares a digital divided sample from the VCO with a very stable and accurate reference frequency, based on a crystal oscillator, and generates
a tuning voltage for the VCO.
RDS GENERATOR
The RDS (Radio Data System) uses a dedicated microprocessor to generate a direct digital RDS signal using a synthesize technology to create a 57Khz signal
at 361Khz sampling rate (over-sampled x 3.2).
It can be programmed using a PC, but stores all information in internal EEPROM memory which stores information after power down for a stand alone operation.
The RDS microprocessor includes all major features for the RDS standard :
The RDS signal is being mixed into the MPX signal with a variable resistor to change to deviation level of the RDS.
MAIN CONTROLLER
monitoring the lock status to power down if out of lock occur due to failure.
On power up, the controller will make test for the PLL operation, will program last frequency from internal EEPROM memory into PLL and wait till frequency
lock.
After frequency lock, it will enable the RF power stage and monitor it while waiting for buttons to be pressed.
Guide for jumper settings
The TX190 is factory set to Stereo operation with RDS on, pre-emphasis of 75uS and limiter on.
Содержание TX190
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