TFT Inc 5290 用户手册

This section describes the theory of operation for the Model 5200 Series STL Transmitter and Receivers. 

The Model 5200 STL Transmitter accepts either balanced or unbalanced composite or monaural audio on 
the rear panel. The composite input level should be 3V

p-p

 for ± 50 kHz deviation. The program input is 

adjusted by R22 on the Main Board. Similarly, there is an unbalanced input for a MUX channel, the level 
of which should be 1.2V

p-p 

for ± 12 kHz deviation. The MUX deviation is adjusted by R29 on the Main 

Board. 

J10 sets the transmitter for “Flat” composite or monaural operation. J11 sets the transmitter pre-emphasis to 
75 µsec; J12 sets the pre-emphasis to 50 µsec.  Only one of these three jumpers should be made at any 
time. 

If the optional SCA generator is utilized, then J19 should be connected between pins 2 and 3; if an external 
SCA generator is utilized, the J19 should be connected between pins 1 and 2. 

The summed output of the program and SCA networks is routed to a 70 MHz VCO Modulator, which 
consists of U14 and U13. Linearity of the modulation is adjusted by R64. 

The 70 MHz modulated VCO output (-18 dBm) is mixed in U27 with a local oscillator (+3 dBm), which 
operates 70 MHz below the output frequency. This on-frequency, modulated signal (-24 dBm) is filtered 
by FL2, then amplified by U28, which adds approximately 30 dB of gain. The output of U28 (+3 dBm) is 
again filtered then amplified by U29, a 15 dB gain amplifier, for a final output from the main board of 
approximately +15 dBm. 

The local oscillator consists of a dual Phase-Lock-Loop, which consists of a TCXO that operates at 20 
MHz and U20 (VCO1), VCO2 and U21. The frequency is referenced to the 20 MHz TCXO and actually 
set by U19 and U24, which are controlled by logic programmed by U1. 

The modulated, on-frequency RF output of the main board is routed to the input of the power amplifier, 
where the signal is furthered amplified and filtered by U1 and strip-line filters on the Power Amplifier 
Board. 

U10, U11, U6A, U8A on the Main Board control lock-out and remote control functions. Metering samples 
for PGM, MUX, FWD PWR, REV PWR, VCO1 bias, VCO2 bias, and VCO3 bias are furnished to U1 and 
subsequently scaled and displayed by the front panel LCD. 

The 5290 Transmitter consists of a Main Board, a Display Board, a Power Amplifier, and a power supply. 
The Main Board contains input processing and metering, the local oscillator, mixer, and RF output circuits. 
The Display Board receives display information from the Main Board for display on the front panel LCD. 
The Power Amplifier amplifies the modulated, on-frequency RF output from the Main Board to the proper 
RF output level on the rear panel. 

 

(To be supplied) 

 

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