HP (Hewlett-Packard) HP 85660B ユーザーズマニュアル

Figure 1. Variable Gain Amplifier, Simplified Schematic

When the 20 K potentiometer is set to zero, the amplifier has a gain of 

 when set to

20 K, the gain is 

 and when set to 10 K, the gain is zero. 

 

 to 

 switch in

different 20 K potentiometers for the five bands. The outputs for the two segments at U2 are
summed together in 

 A waveform similar to Figure 2 is present at the output of 

 if

a full band is swept (for example, 5.8 to 12.5 

 and the oscilloscope horizontal input is

connected to the sweep output of the analyzer. Similarly, the output of 

 will appear as

shown in Figure 3.

Both waveforms (Figure 2 and Figure 3) are summed together at 

 to form a current source

with Q16 to drive the slope attenuator in the 

 Last Converter. The average output

current is set by slope gain adjustment R84.

The slope attenuator in the 

 Last Converter varies the gain of the 21.4 MHz IF with the

collector current of 

 providing gain correction that varies with frequency. Within each

band, there is independent control over two halves of the band, and IF gain that increases or
decreases with increasing frequency.

When Band F (external mixer) is selected, 

 and 

 provide additional gain to make up

for the conversion loss of the external mixer.

 3