R&S®VU825 Power Amplifier

  • Overview

Key Facts

This amplifier operates over a wide band in the frequency range from 87.5 to 108 MHz. The output to a load with VSWR = 1 can be adjusted at least within a range of 0.5...2.7 kW. The power supply is integrated into the amplifier. At rated output and VSWR=1 the line power input is less than 4.7 kW. The amplifier runs up to the operating frequency at any phase relationship with RF power of up to 300 W fed back into the output. The harmonic attenuation at the amplifier output is at least 85 dB at all output values and frequencies. It is not necessary for the customer to trim the amplifier.

  • Integrated Harmonic Filter
  • Hot swappable
  • Self protection and regulation (VSWR, temperature, transistor failure)
  • Advanced Can-Bus diagnostic (relevant parameter / status reports come to CCU)
  • Integrated power supply
  • Phase and gain self adjusted
  • Calibration values stored in amplifier control
  • Gain is controlled by analog communication between Pas

Features & Benefits

The amplifier includes failsafe features to protect it from damage under impermissible operating conditions. However the objective is to continue transmission as long as possible.

The power supply protects itself with an excessive temperature trip (shuts off as long as temperature is excessive), short-circuit current limitation, input voltage and phase monitor and excessive voltage limitation. In the event of a power supply malfunction the amplifier output power is switched off.

If the input signal level is below the range required for reliable operation, the preamplifier power is reduced to a minimum value, the bias voltage for the output stage transformers is switched off and the primary operating voltage is set to a minimum value. A hysteresis feature is provided to prevent the amplifier from switching on and off too rapidly. A soft start is accomplished immediately when the input signal returns.

The power supply as well as the amplifier circuit each have their own excessive temperature trip. When a certain temperature threshold is exceeded the amplifier is shut off. This also ensures that the remaining total dissipation power cannot lead to the unit overheating even in the event of a complete cooling failure. The threshold for excessive temperature switch-off is above the permissible operating temperature.

To ensure transmission for as long as possible, switch-off is accomplished only during the period the temperature is excessive. A hysteresis feature is provided to prevent the amplifier from switching on and off too rapidly. A soft start is accomplished on return.

In the even of strong reflections above a reflection threshold of 2, the power is switched off momentarily, followed immediately by a soft start. The amplifier protects itself if reflection is still present by reducing the output power. The time constant for switch-off must be selected to prevent damage to the amplifier in the event of total reflection and all reflection phase positions.

In the presence of weaker reflections above reflection threshold 1, the output power is only reduced with previous switch-off. When the reflection is not longer present, the power reduction is automatically cancelled.

Reflection threshold 1: Reverse power > 120 W (SWR > 1.5)

Reflection threshold 2: Reverse power > 300 W (SWR > 2)

The amplifier's own combiner includes a monitoring feature for the absorber power to ensure that the resistors are not overloaded when transistors fail, regardless of the number. In the event of a malfunction the setting for the output power is reduced.

Key Facts

  • General information

    This amplifier operates over a wide band in the frequency range from 87.5 to 108 MHz. The output to a load with VSWR = 1 can be adjusted at least within a range of 0.5...2.7 kW. The power supply is integrated into the amplifier. At rated output and VSWR=1 the line power input is less than 4.7 kW. The amplifier runs up to the operating frequency at any phase relationship with RF power of up to 300 W fed back into the output. The harmonic attenuation at the amplifier output is at least 85 dB at all output values and frequencies. It is not necessary for the customer to trim the amplifier.

    • Integrated Harmonic Filter
    • Hot swappable
    • Self protection and regulation (VSWR, temperature, transistor failure)
    • Advanced Can-Bus diagnostic (relevant parameter / status reports come to CCU)
    • Integrated power supply
    • Phase and gain self adjusted
    • Calibration values stored in amplifier control
    • Gain is controlled by analog communication between Pas

Features & Benefits

Failsafe features

The amplifier includes failsafe features to protect it from damage under impermissible operating conditions. However the objective is to continue transmission as long as possible.

Power supply

The power supply protects itself with an excessive temperature trip (shuts off as long as temperature is excessive), short-circuit current limitation, input voltage and phase monitor and excessive voltage limitation. In the event of a power supply malfunction the amplifier output power is switched off.

Input level monitor

If the input signal level is below the range required for reliable operation, the preamplifier power is reduced to a minimum value, the bias voltage for the output stage transformers is switched off and the primary operating voltage is set to a minimum value. A hysteresis feature is provided to prevent the amplifier from switching on and off too rapidly. A soft start is accomplished immediately when the input signal returns.

Temperature monitoring

The power supply as well as the amplifier circuit each have their own excessive temperature trip. When a certain temperature threshold is exceeded the amplifier is shut off. This also ensures that the remaining total dissipation power cannot lead to the unit overheating even in the event of a complete cooling failure. The threshold for excessive temperature switch-off is above the permissible operating temperature.

Temperature monitoring II

To ensure transmission for as long as possible, switch-off is accomplished only during the period the temperature is excessive. A hysteresis feature is provided to prevent the amplifier from switching on and off too rapidly. A soft start is accomplished on return.

Reflection Monitoring

In the even of strong reflections above a reflection threshold of 2, the power is switched off momentarily, followed immediately by a soft start. The amplifier protects itself if reflection is still present by reducing the output power. The time constant for switch-off must be selected to prevent damage to the amplifier in the event of total reflection and all reflection phase positions.

Reflection Monitoring II

In the presence of weaker reflections above reflection threshold 1, the output power is only reduced with previous switch-off. When the reflection is not longer present, the power reduction is automatically cancelled.

Reflection Monitoring III

Reflection threshold 1: Reverse power > 120 W (SWR > 1.5)

Reflection Monitoring IV

Reflection threshold 2: Reverse power > 300 W (SWR > 2)

Absorber monitoring

The amplifier's own combiner includes a monitoring feature for the absorber power to ensure that the resistors are not overloaded when transistors fail, regardless of the number. In the event of a malfunction the setting for the output power is reduced.

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