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SUMMARY

This chapter has presented information on video and rf amplifiers. The information that follows summarizes the important points of this chapter.

A FREQUENCY-RESPONSE CURVE will enable you to determine the BANDWIDTH and the UPPER and LOWER FREQUENCY LIMITS of an amplifier.

THE BANDWIDTH of an amplifier is determined by the formula:

THE UPPER-Frequency response of an amplifier is limited by the inductance and capacitance of the circuit.

THE INTERELECTRODE CAPACITANCE of a transistor causes DEGENERATIVE FEEDBACK at high frequencies.

VIDEO AMPLIFIERS must have a Frequency response of 10 hertz to 6 megahertz (10 Hz - 6 MHz). To provide this Frequency response, both high- and low-frequency compensation must be used.

PEAKING COILS are used in video amplifiers to overcome the high-frequency limitations caused by the capacitance of the circuit.

SERIES PEAKING is accomplished by a peaking coil in series with the output-signal path.

SHUNT PEAKING is accomplished by a peaking coil in parallel (shunt) with the output-signal path.

COMBINATION PEAKING is accomplished by using both series and shunt peaking.

LOW-FREQUENCY COMPENSATION is accomplished in a video amplifier by the use of a parallel RC circuit in series with the load resistor.

A RADIO-FREQUENCY (RF) AMPLIFIER uses FREQUENCY-DETERMINING NETWORKS to provide the required response at a given frequency.

THE FREQUENCY-DETERMINING NETWORK in an rf amplifier provides maximum impedance at the desired frequency. It is a parallel LC circuit which is called a TUNED CIRCUIT.

TRANSFORMER COUPLING is the most common form of coupling in rf amplifiers. This coupling is accomplished by the use of rf transformers as part of the frequency-determining network for the amplifier.

ADEQUATE BANDPASS is accomplished by optimum coupling in the rf transformer or by the use of a SWAMPING RESISTOR.

NEUTRALIZATION in an rf amplifier provides feedback (usually positive) to overcome the effects caused by the base-to-collector interelectrode capacitance.




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