Monitoring of amplifier output signal level - measuring voltage and current to eliminate effects of output side interference

摘要

The monitoring system is used in the output stage of a transmitter, the object being to monitor the output signal level and initiate an alarm if it falls below a set value. The method of monitoring is to measure both output stage voltage and current, and use a combination of these to generate a voltage signal proportional to output level. This signal is then compared with a reference and the resulting error used to initiate an alarm. Voltage and current are typically already measured for output impedance matching, thus little additional circuitry is required. The measurement eliminates the effect of disturbing voltages impressed on the output stage from outside the equipment. Where voltage only is measured such disturbances can effectively mask a low signal level and prevent a legitimate alarm being generated.