Larcan T1000U 1000 Watt UHF Translator User Manual 01 INTRODUCTION rv1

Larcan Inc 1000 Watt UHF Translator 01 INTRODUCTION rv1

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Unit 1 – Introduction

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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 establish 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 2nd UHF converter has an oscillator controlled by PLL (Phase Locked Loop Integrated

Circuit), which frequency is selected through the DIP switch from the Oscillator control board. When

the modulated signal in IF is received in the 2nd converter, it is filtered and applied to a mixer. The

result of this mixing is filtered (channel filter) and supplied to the following modules of the equipment,

in the selected channel.

Unit 1 – Introduction

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2.3. Amplifier Levels:

2.3.1. Comment/Composition/Origin:

The RTU1000T is composed of four 250W amplifier modules that are combined through 3dB

hybrid circuits. A 50W amplifier and 1: 4 hybrid module excite the final modules.

All the amplifiers are completely in solid state.

2.3.2. Protections/Signaling:

Each 250W amplifier has a VSWR protection (Voltage Stationary Wave Ratio), temperature and

limiting power. The output power, VSWR, temperature, current and module voltage can be monitored

through a DB9 connector in the front panel. In the frontal panel also there is the normal power

indication (Green Led), low power (red led) and excessive VSWR (red led). In the output there is the

video and audio power monitoring, antenna VSWR, power supply current and voltage, VSWR

indications, power supply temperature, signal absence, over voltage and over current.

2.4. Notch filter:

It is used to assure the operation of other transmitters in adjacent channels. It is composed by 7

mechanical cavities, 6 are syntonized in the spurious frequencies and 1 in the 2nd harmonic.

Unit 2 – IF Modulator

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1. Audio and Video Modulator:

1.1. Function:

This module function is to generate two carriers: one in 45.75 MHz and the other in 41.25 MHz.

The first is modulated in AM-VSB by a video signal and the other one is modulated in frequency by an

audio signal.

1.2. Block Diagram:

1.3. Technical Description:

1.3.1. Video Modulator:

The transistor Q1 oscillates in the crystal frequency (45.75 MHz - IF video), and the transistor

Q2, with high input impedance, guarantees the isolation to the oscillator Q1 output. The frequency

accuracy is adjusted in the variable inductor L1. The input video signal, with adjustable level in R27

(front panel), is applied to the high impedance input push-pull amplifier formed by transistors Q6 and

Q9. The amplifier output signal modulates in amplitude, in the mixer M1, the video carrier.

The integrated circuits IC18 to IC21 form a group delay predistortion circuit. The syntonized

cells, at the video bandwidth, cause an advancement of 170 ns at 3.58MHz. This video pre-distortion is

inserted in the circuit through jump’s JP5 and JP6. The adjustable attenuator R146 allows equalizing

the video level when the pre-corrector circuit is turned off.

The transistor Q12 receives the video signal, invertes its phase and applies it to the IC7

amplifier. This amplifier causes a non-linear enlargement to the video signal emphasizing the

synchronizing pulses. This signal is clamped in 0.7V by the D5 and is compared to 0.3V (due to diode

D4) in the comparator circuit IC6. In this manner, at the IC6 output, there will be only synchronizing

pulses. These pulses are applied to the IC5 (mono-stable) in the negative transition to generate

clamping pulses. The clamping pulses commute the transistor Q10 that switches the video signal

clamping it to the blanking level through R45. This adjustment allows choosing the point of modulation

in the mixer for a better linearity. If there is lack of clamping pulses, the Q11 transistor commutes,

allowing adjusting through R44 the level of the video carrier without modulation.

The integrated circuit IC9B receives the clamping signal detected through D7, changes its state

and commutes the transistor Q13. It allows switching the external circuits connected to the Automatic

output. The led in the panel shows this operation, when it is green it indicates video on. This circuit

presents about 60 seconds delay time approximately.

Unit 2 – IF Modulator

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The video signal peak is detected through IC8 and through IC9 and it is differentiated with the

level adjusted through R45, in order to extract the dc component.

The IC9A output has a dc level related to the video signal not taking into account the

synchronizing pulses. The 100% video measurement is adjusted through R72 in the meter with a video

signal with 100% APL. The C118 e L18 components form an ICPM corrector circuit that allows

correcting a non-desirable phase-shift at the video carrier caused by the modulating signal.

The modulated video carrier is amplified by IC1 and the SAW filter FL1 filters this signal giving

the final characteristics of the desired modulation, i.e., AM_VSB (amplitude modulation with vestigial

side band). The amplifiers IC2, IC3 and IC4 produce the necessary gain to signal, in order to

compensate the losses in SAW filter and deliver a 0 dBm output level. The output signal level is

adjustable by R12 (front panel), which controls the PIN diode conduction (D1). The trimpot R13 limits

the maximum IF output level and the circuit formed by transistor Q19 and capacitor C120 increases

slowly the output level to eliminate high frequency peaks when the equipment is turned on.

The IF signal, after amplification, passes through a low-pass filter, formed by L6, L7, C21, C22

and C23 to eliminate harmonic signals. Part of this signal is sent to the detector circuit formed by

transistors Q3 and Q4 to measure the IF signal in the panel. The trimpot R24 allows adjusting the

reading level through the meter.

1.3.2. Audio Modulator:

The transistor Q14 and associated components generate the audio carrier. The applied voltage

to the varicap diode D10 controls its frequency. The amplifiers IC12 and IC13 increase the signal level

and through the trimpot R108 is applied to the IF amplifier to be delivered at the output. A sample of

this signal is delivered to the “prescaler” IC14 through R108. It divides the signal into 64 and delivers it

to PLL (integrated IC15). The PLL divides again this signal, now into 66, and compares it with a

reference signal in phase, resulting a voltage proportional to the difference of the phase between the

signals; this voltage is filtered and applied to diode D10 to correct the frequency. The reference

frequency for PLL is generated at the integrated circuit itself that oscillates at 10 MHz and divides it

into 1024. The oscillator crystal is found in a thermal chamber, which is controlled by Q15 and by

thermistor NT1, for better frequency stability. The trimmer C90 allows the fine adjustment of this

carrier frequency (41.25 MHz). If the circuit cannot correct the frequency, the transistors Q17 and Q18

are commuted to turn on the frequency error red led.

The audio signal that will cause the modulation in frequency in this carrier may come from the

mono audio input or stereo audio input. It is possible to select it through jump JP3.

The mono audio input circuit has an unbalanced amplifier IC10 and pre-emphasis circuit. It is

possible to turn off the pre-emphasis through jump JP2. The trimpot R92 (front panel) adjusts the

audio level that will cause the correct modulation index. The integrated circuit IC17 and associated

components form a peak detector of audio signal and a trimpot R117 allows adjusting 100% at the

meter for the correct deviation. The battery input (+36V) through D16 and fuse F1 connects through

connector CN2 the power supply FTE017 (optional).

Obs: The circuit diagram is divided into four parts.

Unit 2 – IF Modulator

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8. Power Supply:

8.1. Function:

The power supply function is to generate +12V and -12V voltage suitable to supply the

modulator.

8.2. Technical Description:

The transformer T1 reduces the input voltage for the rectifiers D1 to D4. The positive and

negative voltage obtained after the rectification and filtering through C1 and C2 are regulated through

IC1 and IC2 to obtain +12V and -12V voltage to supply the Modulator.

8.3. Circuit Diagram FTE015:

Unit 2 – IF Modulator

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9. Power Supply (optional):

9.1. Function:

The switched power supply has the function to generate +12V and -12V voltages from the input

voltages AC or from the +36V battery (opc).

9.2. Technical Description:

The input voltage, after transformer T2 and diodes D1 and D4, supplies the PWM IC1. If there is

no AC the battery voltage supplies the circuit.

The pulses generated by IC1 commute the transistor Q1 and switch the voltage over the primary

T1 at 25 KHz frequency.

The induced pulses that are in the secondary are rectified by D7 and D8 and filtered by C8 e C9. The

regulator IC2 assures the -12V regulated voltage. A voltage sample after L1 supplies the IC1 control

input, through the divider R11 and R12. The pulses that are generated for IC1 have their width

changed in function of the received sample, canceling, in this manner, any variation in the +12V

voltage. The resistor R9 supplies a sampled voltage related to the current which circulates in the output

to the IC1, pin 3. This input protects the over current, reducing the +12V voltage.

9.3. Circuit diagram FTE017:

Unit 2 – IF Modulator

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10. Meter Circuit:

10.1. Function:

The meter circuit allows, through the selector switches and meter, the measurements of the

video modulation, audio modulation and the IF level.

10.2. Circuit diagram CMD001:

Unit 3 – Channel UP Converter

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1. Channel UP converter:

1.1. Introduction:

This module converts an IF signal, into “a” UHF band channel, maintaining its characteristics

and the same bandwidth.

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

The filter and IF amplifier establish the necessary bandwidth to the input signal and supply a

gain in it, maintaining a constant level, through an AGC loop. It is used only in the transposer

equipments.

1.3. IF pre-distortion:

The IF module pre-distortion corrects the intermodulation, the differential gain, the differential

phase and the synchronism compression. This correction is done by pre-distortion on IF level (41-47

MHz). This module is placed after the audio and video modulator and before the channel converter

module.

1.4. Automatic Level Control (ALC):

This module maintains the output peak power at its nominal value, even if there is gain

variation due to the temperature and power supply variations.

It allows a maximum correction of ±1dB.

1.5. Channel converter:

The UHF channel UP converter has an oscillator that is controlled by PLL, whose frequency

operation is selected by DIP switch from the Local Oscillator control board, according to the channel

programming chart.

1.6. Protections/signals:

The channel UP converter has in its front panel a PLL (Phase Locked Loop) alarm led that shows

if the converter is out of the operation frequency.

Unit 3 – Channel UP Converter

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3. IF filter amplifier:

3.1. Function:

The IF filter establishes the adequate bandwidth to the input signal and the IF amplifier supplies

the gain for this signal, maintaining a constant level, through AGC loop.

3.2. Technical Characteristics:

Central Frequency __________________________________________________________________________ 44 MHz

Bandwidth __________________________________________________________________________________ 6 MHz

Input and Output impedance ______________________________________________________________ 50 Ohms

Maximum output level ______________________________________________________________________ +3 dBm

Linearity _________________________________________________________________ + or – 0.25 dB in ± 3 MHz

Maximum gain _______________________________________________________________________________ 60 dB

AGC band ____________________________________________________________________________________ 50 dB

Supply ______________________________________________________________________________ +12V at 250mA

3.3. Block Diagram:

3.4. Technical description:

3.4.1. IF Filter:

The input signal is applied by J1. The integrated circuit IC1 amplifies the applied signal to the

IF filter.

The function of the circuit that is formed by C7, L3, C8, C9, L4, C10, C11, L5, C12, C13, C14

and C16 is to determine the IF amplifier operation bandwidth. This filter is adjusted to obtain a 6MHz

bandwidth.

3.4.2. IF amplifier:

The IF signal received from IF filter is, through C17, connected to the adjustable attenuating

loop, that is formed by diodes D2, R9, D4 and D3. After the attenuating loop, the signal is amplified by

the integrated circuit MAR-7 (IC2).

The amplified signal passes through another attenuating loop, formed by diodes and resistors

D5, R14, D7 and D6, and it is connected by the capacitor C28 to the integrated circuit MAR-6 (IC3),

and finally, through capacitor C29, reaches the integrated circuit MAR-7 (IC4).

A sample signal from the output signal is taken from the resistor R45; after, it is amplified by

transistor Q4 and detected by the diodes D10 and D11. The detected signal by the diode D11 is

supplied, by the emitter follower Q3, to check the IF level in the panel.

The integrated circuit IC5-B supplies in its output a dc level, that is the function of the received

signal J1. The diode D1 and L9 act respectively in the polarization of the attenuating loops, altering the

final gain of the IF amplifier. When JP2 is in the AUT position, this dc level is proportional due to the

detected signal by the diode D10, maintaining the IF level constant in the output J3.

The IC5-A output level is the result of input levels voltage comparison between pins 3 and 2.

This way we can determine the operation point of the IF command adjusting R21. Through CN3-1 the

Unit 3 – Channel UP Converter

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following circuits are enabled.

Unit 3 – Channel UP Converter

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4. IF Pre-distortion linearity:

4.1. Function:

It corrects the non-linearity and/or intermodulation that are generated at the final stage of the

transmitter amplification.

4.2. Technical characteristics:

Frequency band: ______________________________________________________________________ 41 to 47 MHz

Input level: ____________________________________________________________________ -4.0 dBm ± 1.0 dBm

Output level (adj): __________________________________________________________________ + 3.0 dBm (max)

Input/Output Impedance:___________________________________________________________________ 50 ohm

Supply: _______________________________________________________________________________________ +25V

4.3. Technical Description:

IF signal applied to the input J1 is amplified by Q1, and in Q2 is divided in order to supply two

circuits, a linear one and a non-linear one.

The linear circuit has about a 40 ns delay line to compensate the delay caused in the non-linear

circuit. After the delay line, the signal is inserted through trimpot R13 in the adder circuit that is

formed by Q4 and Q5.

The non-linear circuit causes a distortion in the signal trough D3 and D4 that have its

conduction region determined by trimpots R11 and R29. This signal, distorted and amplified by Q7 and

Q8, is put in phase by equalizer circuit formed for L11, C29, R40 and R41, again amplified for Q9, via

trimpot R50 and transistor Q10 and finally is added to the linear signal.

The composed IF signal passes by the attenuator circuit, and its level is adjusted by R44, and

amplified by IC1 when it is delivered to output J2.

4.4. Adjustment Procedure:

The signal should be constantly checked by the spectrum analyzer using the red pattern

modulated signal.

1) Insert the circuit in the system when the IF level is about –3.0 dBm in the input and all the

trimpots are in the minimum.

2) Adjust trimpot R44 to 80% of its course approximately, then increase the level in R13 until

the nominal power is reached.

3) Adjust trimpots R11 and R29 in order to cause the needed distortion to cancel the distortion

that comes from the amplifying final stage, adjusting the level of this signal in the trimpot R50 and

compensating the power variation in the trimpot R13, in order to maintain it as a nominal one. Adjust

the inductor L11 to obtain the distorted signal phase inversion that will be inserted in the system.

Unit 3 – Channel UP Converter

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5. Automatic Level Control (ALC):

5.1. Function:

The Automatic Level Control corrects the transmitter output peak sync power due to the

variation gain of the amplifiers.

5.2. Technical Description:

This circuit has a total attenuation of 1dB, allowing controlling the power to positive and

negative variation of 0.5dB.

The command occurs through the obtained voltage from the TV monitor through wire identified

by the CAP cord. If the Turn on/turn off switch in the panel is OFF, it allows adjusting the output

power, as it fixes the CP input in 3.7V. We can observe in the circuit the variable attenuator by the

diodes PIN formed by diodes D1, D2 and D3, and capacitors C10, C11 to C14 and resistors R14 and

R15.

The Pin diodes current occurs through the integrated circuit IC1A, by shock CH1. The TV

monitor CAP command voltage supplies the IC1A inverter gate through R1. The integrate circuit IC1A

amplifies this voltage increasing its range from –0.5 to -10V.

The integrated circuit IC1B receives this voltage of –0.5 to -10V by R10, adding it to a pre-fixed

value R7, R8 and R9. This causes the IC1B output variation from –1.5 to -8V approximately, causing

the circuit attenuation to PIN diode, which does not exceed a total variation of 1dB.

The divisor formed by R18, R19 and R20, allows obtaining the reference voltage (REF) to

calibrate the transmitter power in the ALC OFF situation.

5.3. Adjustment Procedure:

a) Turn the switch to OFF position (in the panel).

b) Adjust R19 to a 3.7V reading in a digital multimeter in the output REF pin.

c) Adjust the sweep generator, the detector and the oscilloscope to 0dBm IF frequency, inserting the

circuit.

d) Through CN1 turn on R1 to ground.

e) Verify if the attenuation is inferior to 1dB in the oscilloscope and memorize the response.

f) Through CN1, turn on R1 to -12V.

g) Through R9 adjust the attenuation to 1dB in the oscilloscope.

h) Turn off CN1 and adjust R5 to half of the range in the oscilloscope.

i) Insert the circuit between the modulator and the channel converter.

j) The IF level is adjusted to nominal power when the switch is in OFF position.

k) Change to the ON position, verifying the output power.

Unit 3 – Channel UP Converter

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6. Channel UP Converter:

6.1. Function:

The channel UP converter function is to convert the IF frequency (41 to 47 MHz) to a determined

channel in UHF.

6.2. Technical Characteristics:

Input frequency band: ________________________________________________________________ 41 to 47 MHz

Output frequency band:_____________________________________________________________ 470 to 890 MHz

Gain: _________________________________________________________________________________________ 0 dB

Input/Output Impedance: _________________________________________________________________ 50 Ohms

Channel bandwidth: _________________________________________________________________________ 6 MHz

Consume: __________________________________________________________________________ +12V at 150mA

6.3. Block Diagram:

6.4. Technical Description:

The oscillator, transistor Q2, generates a low noise signal in the used frequency band. Its

frequency is determined by the control voltage applied to diode varicap D2. The amplifier IC3 receives

the oscillator signal and provides load isolation and, the amplifier IC2 delivers to the mixer a +17 dBm

level. A sample from the oscillator signal is, through R25, delivered to IC7 prescaler, that divides the

signal into 64 and 65, according to the control that comes from PLL, integrated circuit IC8. PLL receives

the prescaler signal and divides it according to the external programming (1 to 8), and compares it in

phase to a reference signal controlled by crystal generated by the own integrated circuit.

In the integrated circuit output results a proportional voltage that is the phase difference among

the signals. This voltage is filtered by IC5 and applied to diode D2 for the frequency correction

The mixer MX1 receives IF signals and the local oscillator, and generates through the signal

beating the desired channel. The conversion loss in the mixer is aproximately 8dB at most. The signal

after the mixer passes through the channel filter that rejects the local oscillator and the undesirable

product in the conversion. The amplifier IC1 compensates the mixer and the channel filter losses.

6.5. System alignment:

1. Program the oscillator according to the given channel chart and with a multimeter in PT2,

adjust trimmer C21 to a 4.5V reading. The led helps the adjustment, when it is turned off it indicates

that the oscillator is in the desired frequency. In the point meas. at oscillator shows 0.5V level

indicating the RF presence that comes from the local oscillator.

2. Put the sweep generator in the IF band in 41 to 47 MHz, and apply to the IF input, in JP1.

Adjust the channel filter to the maximum gain and a better linearity, with the detector in the channel

output.

Unit 3 – Channel UP Converter

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7. PLL protection:

7.1. Function:

This circuit function is to turn off the transmitter.

7.2. Technical Description:

The DC voltage that comes from the channel converter, more precisely from the channel

converter Led diode, is applied to the comparator through diode D1 by resistor R1 and reaches circuit

integrated IC1pin 3.

Through the adjustment in the trimpot R3, we can act in the integrated circuit comparison,

moving pin 1 to high level (operational gain X comparing voltage). Then, through diode D2 this voltage

is applied to CA output (High level) or CB (Low level), by the transistor Q1 collector saturation.

7.3. Circuit diagram PRT007:

Unit 3 – Channel UP Converter

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8. UP Converter supply -12, +12 and +24V:

8.1. Function:

The power supply function is to generate -12V, +12V and +24V voltage suitable to supply the UP

Converter.

8.2. Technical Description:

The main AC input voltage is reduced by the transformer T1.

T1 has two secondarie winds, one for the +24V and the second for the +12V and –12V supplies.

D1, D2, D3 and D4 rectifiers the secondary voltage that is filtered by the capacitor C1. IC1 is a

linear regulator that feeds +24V at the output.

D5 and D6 are the retifier diodes for the positive voltage filtered by C4.

IC2 is a linear regulator for the +12V output supply.

In the same manner there are a rectifier and a linear regulator for the negative voltage –12V.

Unit 4 – 50W Exciter

- 2 -

1. 50W Exciter:

1.1. Introduction:

This module amplifies the signal power that comes from the channel converter, to the 50 W

level, maintaining its characteristics and the same bandwidth.

1.2. Protections and Monitoring:

We have for these functions:

VSWR Circuit: it protects the amplifier module transistors, when the output stationary wave is

superior to 4%. This circuit acts in the output transistors gates.

Temperature Circuit: it acts in the output transistors gates when the heat sink temperature is above

56°C

Forward RF Power Circuit: it acts in the output transistors gates when the output RF power

overcomes the pre-fixed value limiting, in this manner, the maximum RF forward power.

1.3. Power Supply input:

This circuit supplies information from the amplifier currents.

1.5. Amplifier Stages:

This module has two UHF amplifier stages in cascade, the first of 2W and the second of 50W.

Unit 4 – 50W Exciter

- 5 -

3. Amplifier protection:

3.1. Function:

This module function is to protect the amplifier modules against an excessive VSWR, RF power

and temperature.

3.2. Technical Description:

The informations from forward RF power and VSWR are obtained through the Directional

Coupling detectors from the amplifier output.

The proportional voltage to the RF forward power supplies the isolator amplifier integrated

circuit IC5A. This amplifier output, supplies IC5B and IC2A comparator circuits. The integrated circuit

IC5B acts as a RF power limitator, and if the RF forward power overcomes the pre-fixed value by

trimpot R31, transistor Q1 conducts by diode D3, and resistor R39, removing the gate polarization

voltage from the 50W final amplifier. The integrated circuit IC2A compares the RF forward power to an

adjusted value in –3dB by trimpot R10, so that the RF forward power green Led lights in the panel. The

integrated circuit IC2B is an inverter amplifier, be that, when the RF forward power drops lower than –

3dB, its output reaches +12V what lights the RF forward power red Led in the panel.

The VSWR proportional voltage supplies the insulator amplifier integrated circuit IC4A. The

IC4A output supplies the IC4B comparator input and also the monitoring in the panel by R1.

If the RF signal exceeds the value that is pre-fixed by trimpot R24, the VSWR Led in the panel

lights and transistor Q1 conducts by diode D5 and resistor R39, removing the polarization from the

output amplifier transistor.

A temperature sensor protects the temperature. This sensor supplies a proportional voltage to

the temperature monitored from 10mV/°C, be that, if the temperature is 50°C we have 500mV.

Through the IC3A isolator amplifier, this voltage is compared to a pre-determined value by trimpot R17

and it is also sent to the frontal panel. The integrated circuit IC3B lights the temperature Led in the

panel and by transistor Q1, diode D4 and resistor R39, it is removed the polarization from the final

amplifier transistors.

The diodes D1 and D2 and the fixed voltage regulator IC1 are responsible for the +12V power

supply that supplies the several protection IC’s.

Unit 4 – 50W Exciter

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4. Power supply input:

4.1. Function:

This circuit function is to protect the power supply, if there is a short-circuit and provides the

amplifier current monitoring.

4.2. Technical description:

The +32Vdc voltage that comes from the three-phase fixed power supply supplies the fuses F1

and F2.

The fuse output F1, by resistors R1 and R2, supplies the 50W final amplifier. The amplifier

current can be monitored by the voltage drop over R1 and R2.

The fuse output F2, by resistor R3, supplies +24Vdc power supply regulator integrated circuit

IC3. Also, through the voltage drop over resistor R3, the 2W amplifier current can be monitored.

4.3. Circuit Diagram ENT002:

Unit 4 – 50W Exciter

- 11 -

5. 2W Amplifier:

5.1. Function:

The 2W UHF amplifier stage amplifies the channel converted to 2W maximum level.

5.2. Technical characteristics:

Gain: ________________________________________________________________________________________ 30 dB

Supply: _____________________________________________________________________________________ +32Vdc

Total current: ___________________________________________________________________________________ 1 A

5.3. Technical Description:

This module is composed of driver amplifier IC1 and the final amplifier Q1.

Trimpot R4 sets the quiescent current of Q1 and D1 and allows controlling the output power for

protection purposes.

At the input, there is a local oscillator filter TLE, C4 and C5.

Unit 4 – 50W Exciter

- 14 -

6. 50W amplifier:

6.1. Function:

The 50W exciter amplifier stage, receives the 2W amplifier signal and delivers it to 1:4 divider of

250W amplifiers with a maximum 50W power.

6.2. Technical characteristics:

Input power: ____________________________________________________________ 2W (Sync and Audio carrier)

Output power: ______________________________________________________________________ 50W Peak Sync

Gain: ________________________________________________________________________________________ 18 dB

Supply: _____________________________________________________________________________________ +32Vdc

Total current: ___________________________________________________________________________________ 5 A

Setting temperature:___________________________________________________________________________ 56°C

6.3. Technical Description:

This module is composed by a LDMOS transistor.

Trimpot R4 sets the quiescent current of Q1 and D1 allows controlling the output power for

protection purposes.

Unit 5 – 250W Amplifier

- 2 -

1. 250W Amplifier:

1.1. Introduction:

This module amplifies the RF power that comes from 1:4 divisor to 250W, then they are

combined to obtain the 1000W RF power, maintaining its characteristics and the same bandwidth.

1.2. Protections and Monitoring:

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 gates.

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

56°C.

Forward power circuit: it acts in the output transistors gates when the RF output power exceeds the

pre-fixed value, this way limiting the maximum RF power.

1.3. Power supply input:

The protection fuses are in this circuit.

This circuit supplies the informations about the amplifier currents.

1.5. Amplifier stages:

Two 125W amplifier modules are used in parallel. This module uses 4 transistors MRF 373 A. Its

gain is approximately 18 dB in AB class.

Unit 5 – 250W Amplifier

- 5 -

3. Amplifier protection:

3.1. Function:

This module has the function to protect the amplifier modules against an excessive VSWR, RF

power and temperature.