Theory of Operation
2715 Spectrum Analyzer Service Manual 3-9
Circuit Description
The following sections provide detailedcircuit descriptions and is arranged to
follow the input signal flow. While readingthese descriptions, refer to the
corresponding diagrams in Section9: Diagrams.

Attenuator and 1st Converter

The Attenuator and 1st Converter signal path consists of the following parts:
HStep Attenuator
H1.8 GHz Low Pass Filter (2.2 GHz Low Pass Filter for Option 50 and Option
75)
HMixer
H4.5 GHz Low Pass Filter
H2110 MHz Bandpass Filter
The Spectrum Analyzer input frequencyrange is 9 kHz to 1.8 GHz (2.15 GHz
for Option 50 and Option 75). The low end of the frequencyrange is determined
by a capacitor on the Attenuatorboard, the narrowest resolution filter in the
VariableResolution assembly, and FM characteristics of the 1st LO (YIG
Oscillator).
The signal comes in at the frontpanel RF INPUT connector. The 75 ΩRF
INPUT connector is connected to a 0 to 50 dB step att enuator, capable of
stepping from 0 to 50 dB in 2 dB steps. The Attenuator consists of relay
controlled pads of 2, 4, 8, 16, and20 dB. The instrument firmware controls the
relays to provide the necessary attenuati on to maintain a calibrated reference
level.

Step Attenuator