User`s guide

7-4
Operating Concepts
System Operation
The Built-In Synthesized Source
The analyzer’s built-in synthesized source produces a swept RF signal or CW (continuous
wave) signal in the range of:
• 8753ES: 30 kHz to 3.0 GHz (with Option 006: 30 kHz to 6.0 GHz)
• 8753ET: 300 kHz to 3.0 GHz (with Option 006: 300 kHz to 6.0 GHz)
The RF output power is leveled by an internal ALC (automatic leveling control) circuit. To
achieve frequency accuracy and phase measuring capability, the analyzer is phase locked
to a highly stable crystal oscillator. For this purpose, a portion of the transmitted signal is
routed to the R channel input of the receiver, where it is sampled by the phase detection
loop and fed back to the source. Some portion of the RF source signal must always be sent
to the R channel input. The level must be between 0 dB and −35 dBm.
The Source Step Attenuator
The step attenuator contained in the source is used to adjust the power level to the test
device without changing the level of the incident power in the reference path.
The Built-In Test Set
The 8753ES features a built-in test set that provides signal-separation devices and
connections to the device under test. The signal separation devices are needed to separate
the incident signal from the transmitted and reflected signals. The incident signal is
applied to the R channel input through a jumper cable on the front panel. Meanwhile, the
transmitted and reflected signals are internally routed from the test port couplers to the
inputs of the A and B sampler/mixers in the receiver. Port 1 is connected to the A input and
port 2 is connected to the B input. A transfer switch routes the source output power to
either port 1 or 2, allowing measurements to be made in both the forward and reverse
directions.
The 8753ET features a built-in test set that provides signal-separation and connections to
the device under test. Part of the source output is coupled off and applied to the R input as
the incident signal. The reflected signal is routed from the port 1 coupler to the input of the
A sampler. The transmitted signal is routed from port 2 to the B sampler input.
The Receiver Block
The receiver block contains three sampler/mixers for the R, A, and B inputs. The signals
are sampled, and mixed to produce a 4 kHz IF (intermediate frequency). A multiplexer
sequentially directs each of the three IF signals to the ADC (analog to digital converter)
where it is converted from an analog to a digital signal. The signals are then measured and
processed for viewing on the display. Both amplitude and phase information are measured
simultaneously, regardless of what is displayed on the analyzer.