Agilent Technologies LO Frequency Accuracy and Stability , Differences Between Internal and External R Channel Inputs

2-10
Making Mixer Measurements (Option 089 Only)
Measurement Considerations
Frequency offset measurements do not begin until all of the frequency offset mode
parameters are set. These include the following:
• Start and Stop IF Frequencies
• LO frequency
• Up Converter / Down Converter
• RF > LO / RF < LO
The LO frequency for frequency offset mode must be set to the same value as the external
LO source. The offset frequency between the analyzer source and receiver will be set to thi s
value.
For a single-sideband mixer measurement, the RF source can be offset in frequency from
the input receiver frequency, allowing for a swept RF stimulus over one frequency range
and measurement of the IF response over another (in this case the output IF).
When frequency offset mode operation begins, the receiver is tuned to the enter ed IF si gnal
frequencies and then offsets the source frequency required to produce the IF. Therefore,
since it is the analyzer receiver that controls the source, it is only necessary to set the start
and stop frequencies from the receiver.
LO Frequency Accuracy and Stability
The analyzer source is phaselocked to its receiver through a reference loop. In the
frequency offset mode, the mixer under test is inserted in this loop. To ensure that the
analyzer phaselocks correctly, it is important that y ou use an LO source tha t has freque ncy
accuracy better than ±16 MHz and residual FM < 20 kHz RMS.
Differences Between Internal and External R Channel Inputs
Due to internal losses in the analyzer's test set, the power measured internally at the R
channel is 16 dB lower than that of the source. To compensate for these losses, the traces
associated with the R channel have been offset 16 dB higher. As a result, power measured
directly at the R channel via the R CHANNEL IN port will appear to be 16 dB higher than
its actual value. If power meter calibration is not used, this offset in power must be
accounted for with a receiver calibration before performing measurements.
The following steps can be performed to observe this offset in power:
1. To set the power range to manual, press:
NOTE Since the default source output power of the 8722ES is below 0 dBm, no
reduction in source output power is required for this procedure.
Power
PWR RANGE MAN
0x1