Theory of Operation
3-14 2715 Spectrum Analyzer Service Manual
110MHz Bandpass Filter. This filter is a 5th order, shunt resonator Butterworth
filter.
3rd Mixer.U 665 and its associated circuitry make up the 3rd mixer.
Output Amplifier. This IF amplifier consists of a common emitter transistor
(Q670) with both series and parallelfeedback. The 1:1 transformer (T670)
provides lower output impedance for betterintermodulation distortion perfor-
mance. The resistive attenuatorat the output is used to match the load to the
variable resolution. It also providessome high frequency roll off.
1st LO Interface, 1st LO, and 1st LO Buffer Amplifier
This section contains a detailed des cription of the 1st LO Interface, 1st LO and
1st Buffer Amplifier.
The 1st LO has a tuning range of 2.11to 3.91 GHz (2.11 to 4.26 GHz for Option
50 and 75). The oscillator assembly includesthe interface circuit board that
couples operating and tuning voltagesfrom the Center Frequency Control board.
Two Zenerdiodes on the Interface board clamp transient voltages from the main
coil. See Figure 3--6.
−V
1stLO1stLO Interface
+Main
−Main
+FM
SWP Main
−FM
YIGSphere
1stLO Out to 1st LO
BufferAmplifier
Figure 3- 6: 1st LO Interface and 1st LO Diagram

1st LO Interface

and 1st LO