RF Technology R150 Instrucciones de operaciones descargar pdf (Pagina 13)

RF Technology T70/T150 Page 13

5 CIRCUIT DESCRIPTION 5.3 Power Amplifier

tuning voltage which is smoothed by the loop filter components to bias the V.C.O.

varactor diode D3.

5.3 Power Amplifier

The 10 mW output from the main board connects to the power amplifier board

through a short miniature 50 Ohm coaxial cable.

Q2 on the power amplifier board increases the signal to approximately 200 mW. The

bias current of Q2 is controlled by Q1 and the power levelling circuitry to adjust the

drive to the output module U2.

U2 increases the power to 30 watts before it is fed to the directional coupler, low pass

filter and output connector. The directional coupler detects the forward and reverse

power components and provides proportional dc voltages which are amplified by U1a

and U1b.

The forward and reverse voltages from U1a and U1b are compared to the DC

reference voltage from RV1. The difference is amplified by U1c, Q3 and Q4. The

resulting control voltage supplies Q2 through R10, R12 and completes the power

levelling control loop.

5.4 Temperature Protection

Thermistor RT1 on the power amplifier board is used to sense the case temperature of

the output module U2. If the case temperature rises above 90 degrees C., the voltage

across RT1 will increase and transistor Q5 will be turned on. This reduces the dc

reference voltage to the power regulator which in turn reduces the output power by 6-

10 dB.

5.5 600Ω Line Input

The 600Ω balanced line input connects to line isolation transformer T1. T1 has two

150Ω primary windings which are normally connected in series for 600Ω lines. The

dual primary windings can be used to provide DC loop PTT signaling or a 2/4 wire

hybrid connection. All four leads are available at the rear panel system connector.

The secondary of T1 can be terminated with an internal 600Ω load through JP5 or left

un-terminated for high impedance applications.

5.6 Direct Coupled Audio Input

A high impedance (10kΩ) direct AC coupled input is available at the system

connector. The direct coupled input connects to U9a which is configured as a unity

gain bridge amplifier.

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RF Technology R150 Instrucciones de operaciones Pagina 13