Crescend Technologies C7 SERIES Manual de instalação e serviço - Página 13

Procurar online ou descarregar pdf Manual de instalação e serviço para Amplificador Crescend Technologies C7 SERIES. Crescend Technologies C7 SERIES 17 páginas. Continuous duty power amplifier

Imprimir página

PRINCIPLES OF OPERATION

4.1.

INTRODUCTION

This section contains principles of operation of the C7 Series of RF Power Amplifiers.

4.2.

RF INPUT SIGNAL

The amplifiers are set at the factory to work over different input power ranges. The

available range of inputs for different frequency ranges may be found in Table 1-2.

4.3.

RF OUTPUT LOAD

The load impedance should be as good as possible (VSWR <1.2:1) in the working band for

good power transfer to the load and maximum amplifier efficiency.

4.4.

FUNCTIONAL DESCRIPTION

The amplifier is a single channel CW amplifier that operates in various frequency bands

from 30 MHz to 942 MHz. The amplifier specifications are listed in Tables 1-1 and 1-2.

4.4.1.

MAIN RF PATH

The typical main RF path consists of an input attenuator, rf amplifier , rf detectors and

harmonic filter. The circuitry becomes active upon the sensing of rf input power. This

occurs when rf input reaches approximately 3 dB below the low end of the input power

range.

4.4.2.

LOOP CONTROL

The loop control circuitry works to maintain a constant output power versus variations in

DC voltage, rf input power, frequency and load. A coupled detector at the output

monitors the final RF output level and generates a DC voltage proportional to the RF

output level. This voltage is fed back to the controller. The circuitry compares this voltage

to a reference voltage and varies the gain of the amplifier to maintain a constant output.

4.4.3.

VSWR PROTECTION

Reflected power is detected at the output of the amplifier and compared to forward

power. When reflected power reaches an equivalent VSWR of approximately 2.5:1, the

amplifier output is reduced to protect the finals and the front panel HIGH VSWR LED

activates. The higher the load VSWR, the more the output power is reduced.

4.4.4.

THERMAL PROTECTION

The heat sink temperature is monitored with a thermostat. When the heat sink

temperature reaches an unsafe level, the output power of the amplifier is reduced by

approximately 50%. This keeps the channel on the air while still providing some short

term protection until the customer can address the underlying cooling issue.

4.5.

AMPLIFIER COOLING

The amplifier is cooled with forced air over a large heat sink. The fan draws in ambient air

from the front. It is important to maintain a minimum clearance of 3 inches in front of and

behind the amplifier to allow for best cooling of the amplifier.

040003A005 Rev 1