Rf Section Theory Of Operation; Input Attenuator; Low Pass Filter; Preselector Filters - Keysight N9000A Service Manual

RF Section Troubleshooting

RF Section Theory of Operation

RF Section Theory of Operation

Input Attenuator

The input attenuator has 50 dB of attenuation adjustable in 1 dB steps. The
attenuator is built in two stages: A 20dB power stage and a 31dB x 1dB steps
variable attenuator.

Low Pass Filter

While in low band, the low pass filter works as pre-filter to pass the low band
frequencies.

Preselector Filters

The preselector filters are used for high band input frequencies. There are six
groups of preselector filters, whose main purpose is to filter out unwanted spurious
or image response signals.

Mixer

There are three mixers that reside on this assembly.
The first mixer is used to upconvert the low band signal to first IF frequency
3947.5 MHz, while down convert the high band signal to first IF frequency
1228.75 MHz.
The second mixer is used to down convert first IF signal to second IF frequency
322.5 MHz.
The third mixer is used to convert the 322.5 MHz second IF to 22.5 MHz.
st
1 IF Amplifier
This filter is centered around the first IF frequency and to reject the image
frequency.
st
1 IF Filter
This filter is centered around the first IF frequency and to reject the image
frequency.
nd
2 LO
The 2nd LO signal reside on this assembly for use as LO for the second mixer.
128 Chapter 4