Larcan T5000U User Manual

Unit 1 – Introduction

2. General Technical Descriptive:

2.1. IF Modulator (for transmitter):

This is the input module. It is a professional audio and video modulator. The audio and video
signals are applied to their respective input for the modulation process in IF (41 to 47 MHz]. The audio
and video input impedances are 600 balanced Ohms and 75 unbalanced Ohms, respectively.

2.1.1. Video processing:

The video signal passes through linearity correction circuits and then is applied to the 45.75
MHz video modulator. There are Synchronizing Separation circuits that generate the auxiliary outputs
to “Automatic Circuits”. The video signal is also applied to a group delay predistortion circuit.

2.1.2. Audio processing:

The Mono-audio signal or stereo base band is applied to the module and modulates a 41.25
MHz audio carrier.

2.1.3 Module output:

Both carriers, audio and video modulated (41.25 and 45.75 MHz), are applied to the “Vestigial
Side Band Filter” (SAW Filter). At the output there is a circuit to control the IF output level.

2.2. UHF UP Converter:

2.2.1. Introduction:

This module converts an IF frequency signal into an UHF band channel, keeping its
characteristics and the same bandwidth.

2.2.2. IF filter and AGC amplifier (for transposer):

The IF amplifier and filter module establishes the adequate bandwidth for the input signal and
supply the gain in this signal, keeping the level constant through an AGC loop.

2.2.3. Technical Descriptive:

The 2
Circuit), which frequency is selected through the DIP switch from the Oscillator control board. When
the modulated signal in IF is received in the 2
result of this mixing is filtered (channel filter) and supplied to the following modules of the equipment,
in the selected channel.

nd

UHF converter has an oscillator controlled by PLL (Phase Locked Loop Integrated

nd

converter, it is filtered and applied to a mixer. The

- 11 -

Unit 1 – Introduction

2.3. Amplifier Levels:

2.3.1. Comment/Composition/Origin:

The RTU5000T is composed for eight 625W amplifier modules combined through 3dB hybrid
couplers.

The final modules are drived by an 100W amplifier and 3 dB hibrid couplers as splitters.

All the amplifiers are in solid state.

2.3.2. Protections/Signaling:

Each 625W amplifier has a VSWR protection, temperature and a power limiting circuit.

The output power, VSWR, temperature, current and module voltage can be monitored through a
DB9 connector in the front panel.

In the frontal panel there are the normal power indication (Green Led), low power (red led) and
excessive VSWR (red led). There is, also, a BNC connector for monitoring the output signal of each
module.

At the transmitter output, there is the video and audio power monitoring, antenna VSWR, power
supply antenna, current and voltage and indications of excessive VSWR, excessive filter VSWR, power
supply temperature alarm, video absence, phase fail and others.

There is at the transmitter top, a DB25 connector with transmitter signals, for remote
monitoring.

2.4. Notch filter:

It is used to attenuate out channel spurious generated by the transmitter. It is composed by 11
cavities, 10 are syntonized in the spurious frequencies and 1 in the 2

nd

harmonic.

- 12 -

4. Block Diagram:

Unit 1 – Introduction

- 14 -

Unit 4 – UHF 100W Amplifier

1. UHF 100W Amplifier:

1.1. Introduction:

This module amplifies the signal that comes from the channel converter, to the 100 W level,
maintaining its characteristics and the same bandwidth.

1.2. +32V 14A switched power supply:

Its function is to supply the 2 W and 100W modules and also the protection circuits that
compose the unit.
It is necessary a 220VCA transformer with 35V 15 A output to supply it.

Its efficiency is about η = 80%.

1.3. 100W Amplifier protections:

For these functions, we have:

VSWR Circuit: it protects the amplifier module transistors, when the output stationary wave is
superior to 4%. This circuit acts in the output transistors gate.

Temperature Circuit: it acts in the output transistors gate when the heat sink temperature is above
56°C.

Over voltage Circuit: this circuit avoids that voltages upper than 32V supply the amplifier modules.
When this circuit starts operating the 15 A F1 and F2 fuses damage.

1.4. Power detecting and power limiting protection:

This detector function is to transform a RF signal sample in voltage DC. This voltage, that is
proportional to the RF signal, reaches the power limitig circuit to protect the amplifier modules.

1.5. Amplifier stages:

2 W and 100W amplifier modules are used. For this amplifier stages, we use 1 transistor
MRF373A for 2W and 4 transistors MRF 373A for 100W. Its gain is about 50 dB in class AB.

- 2 -

2. Frontal and back panel:

2.1. Frontal Panel:

Unit 4 – UHF 100W Amplifier

Each element in the panel has the

following function:

1.

Circuit Breaker: Protection circuit

breaker 7 A.

monitoring the RF output signal in the
spectrum analizer.

measurements, current, forward power and
VSWR, according the selector switch position.

switch position, the values are indicated in the
meter.

led lights, it indicates an over temperature.

lights, it indicates an exceeding VSWR.

which cools the final amplifier heat sink.

2.

Monitor: Connector (BCN) is used to

3.

Meter: it allows visualizing +32V

4.

Selector switch: according to the

5.

Temperature Led alarm: When the

6.

VSWR Led alarm: When the led

7.

Air input: there is a fan inside it,

- 3 -

Unit 4 – UHF 100W Amplifier

2.2. Back Panel:

Each element in the panel has the

following function:

1.

RF OUT: RF signal output by via

connector N.

frontal panel, cools the heat sink and the hot
air leaves by the back panel.

N.

supply 220V.

2.

AIR OUT: The air enters through the

3.

RF IN: RF signal input by connector

4.

MAIN AC 220V: main AC power

- 4 -

Unit 4 – UHF 100W Amplifier

3. Switched power supply +32V 14A:

3.1. Function

The function of this is to provide 32Vdc with 14 A to the 100W amplifier module.

3.2. Technical characteristics:

Input voltage: __________________________________________________________________ 35Vca ± 10% to 15 A
Output voltage: ____________________________________________________________ 32Vdc to 14 A maximum

3.3. Technical description:

The integrated circuit IC1 operates as PWM (Pulse Width modulator).
In the IC1 pins 11 and 12 , we have the IC supply voltage that comes from zener D1. The power
supply Soft Start is effected by capacitor C9 1µF with resistor R7 10K, acting in pin 4 of IC1. The power
supply oscillation is determined by capacitor C14 and by resistor R8. In pin 9 and 10 from integrated
circuit TL494 we have pulses that will activate the current drivers Q1 and Q2.
This sample is transferred to transformer T1 that will activate, through its secondary, the FET’s
Q5 and Q6. D6 is a fast diode used in switching to avoid reverse voltages in the FET’s. T2 function is to
isolate switched power supply from the continuing voltage and also, with capacitors C18, C19, C20,
C21 and C22 form the filter LC from the power supply. The Shunt RSC is a resistor of low ohm value,
made of nickel/chrome which value does not vary due to the circulating current. The power supply
module formed by R12 and R11//R10 determines the power supply voltage. The sample of this voltage
acts in pin 1 from integrated circuit TL494. Any variation in the output voltage is compensated in pin 1
that acts in the pulse width or shut in pins 9 and 10. The resistors R5 and R6 and capacitor C13 act in
the power supply loop. This means the quickness with which the output maintain constant due to the
current sudden variation. The over current circuit is formed by Q3, Q4, D4, R13 and associated parts,
that act in pin 1 from IC1, decreasing the output voltage to currents upper than 23 A.
The capacitors C1 to C4 and C5 to C7 form an input filter CA after the rectification, and C5 to
C7 are 220 µF capacitors of special manufacture (HFC). These capacitors are used for switching and
cannot be substituted for any other type of capacitors.

- 5 -