6. The noise figure expresses the relative merit
of a receiver which, if
perfect, would have a noise figure of 0 decibel (db).
The noise figure of an RF
c. high transconductance
d. bandwidth-increasing circuits, step-up input transformers, or low input
Assume that the circuit shown in figure 1-3 is the amplifier in an FM tuner.
The electron tube used in the circuit is a 6BJ6 remote cutoff tube whose Eg-Ip curve
is shown in figure 1-4. Assume also that the screen-grid current is 3 ma.
Exercises 7 and 8 are based on the above situation.
7. When the circuit is operating normally as an RF amplifier in an FM receiver,
the grid bias is -1 volt. The value of R1 required to develop this voltage must be
a. 80 ohms.
b. 100 ohms.
8. Assume that the control-grid bias on the 6BJ6 tube is changed to -2 volts.
Without automatic volume control (AVC), the plate current will increase 4 ma when
the signal on the grid increases 1 volt.
When an AVC potential of -4 volts is
applied, an increase of 1 volt in the signal will cause the plate current to
a. less than 0.25 ma.
b. between 0.25 ma and 0.50 ma.
c. between 0.50 ma and 1 ma.
d. more than 1 ma.
9. The bandwidth of the input circuits of an RF amplifier such as shown in A of
figure 112 (TM 11-668) might be increased by either
a. moving the coils closer together or using coils with higher Q.
b. using coils with higher Q or incorporating additional tuned circuits.