
ES User’s Guide
5-21
Optimizing Measurements
Measuring Devices with Long Electrical Delay
Measuring Devices with Long Electrical
Delay
When making narrowband-receiver measurements of devices with long
electrical delay, measured levels can be affected by the rate at which the
source is changing frequency. This sensitivity is related to the time
required for the source signal to travel through cables or devices which
are connected between the analyzer’s two test ports. Since the source
frequency is changing rapidly during a sweep, a long distance or delay
between the analyzer’s two test ports will mean that the signal arriving
at the input port will be of slightly lower frequency than the output
signal at the same moment in time. This effect is referred to as
"frequency shift." The amount of frequency shift is given by the following
equation:
The narrowband receiver at the analyzer’s input port is tuned to the
exact frequency being emitted at the analyzer’s output port, with an
input bandwidth determined by the system-bandwidth selection. If the
input signal is lower in frequency than the output signal, the
measurement of the input signal will be attenuated by the frequency
response of the system bandwidth. The amount of attenuation increases
as the amount of frequency shift increases. The amount of attenuation
also increases as system bandwidth decreases.
The analyzer has been designed to minimize the effect of frequency shift
when a short cable is connected between the analyzer’s two test ports.
When a long cable (or a device with long electrical delay) is connected,
however, it is possible for the measurement to be affected, especially at
the analyzer's fastest sweep rates. If frequency shift is suspected, use the
following techniques to reduce its effect:
• Increase sweep time.
• Decrease frequency span.
• Select a wider system bandwidth.
• Use shorter cables to connect the DUT to the analyzer.
• Use broadband detection to completely eliminate the effect of
frequency shift.
frequency s hift
transit time
frequency span
sweep time
-----------------------------------------
×
=
Summary of Contents for HP 8712ES
Page 8: ...viii ES User s Guide ...
Page 17: ...ES User s Guide 1 1 1 Installing the Analyzer ...
Page 34: ...1 18 ES User s Guide Installing the Analyzer Preventive Maintenance ...
Page 35: ...ES User s Guide 2 1 2 Getting Started ...
Page 52: ...2 18 ES User s Guide Getting Started Performing the Operator s Check ...
Page 53: ...ES User s Guide 3 1 3 Making Measurements ...
Page 135: ...ES User s Guide 4 1 4 Using Instrument Functions ...
Page 159: ...ES User s Guide 4 25 Using Instrument Functions Using Markers Figure 4 15 Delta Marker Mode ...
Page 165: ...ES User s Guide 4 31 Using Instrument Functions Using Limit Testing Figure 4 16 Limit Lines ...
Page 224: ...4 90 ES User s Guide Using Instrument Functions Using an External VGA Monitor ...
Page 225: ...ES User s Guide 5 1 5 Optimizing Measurements ...
Page 246: ...5 22 ES User s Guide Optimizing Measurements Measuring Devices with Long Electrical Delay ...
Page 247: ...ES User s Guide 6 1 6 Calibrating for Increased Measurement Accuracy ...
Page 281: ...ES User s Guide 7 1 7 Front Rear Panel ...
Page 306: ...7 26 ES User s Guide Front Rear Panel Line Module ...
Page 307: ...ES User s Guide 8 1 8 Hardkey Softkey Reference ...
Page 410: ...8 104 ES User s Guide Hardkey Softkey Reference Z ...
Page 411: ...ES User s Guide 9 1 9 Specifications ...
Page 469: ...ES User s Guide 10 1 10 Safety and Regulatory Information ...
Page 475: ...ES User s Guide 10 7 Safety and Regulatory Information Regulatory Information ...
Page 476: ...10 8 ES User s Guide Safety and Regulatory Information Regulatory Information ...
Page 477: ...ES User s Guide 11 1 11 Factory Preset State and Memory Allocation ...