HP 83487A User Manual page 77

C A U T I O N
less without the attenuator, then you had compression during the initial mea-
surement; the second measurement with the attenuator and associated offset
adjustment is the accurate measurement.
Using the fixed 5 dB attenuator
The HP 83487A is shipped with a nominal 5 dB attenuator (±1.5 dB), which
will provide correct attenuation for most signals up to –5 dBm average power
(the current allowable standard). Follow the procedure outlined above to use
this attenuator and enter in the correct offset value.
For many signals, the easiest way to proceed is to always use the attenuator
with the correct offset. A couple of exceptions to this recommendation are:
• when you are splitting the signal for multiple tests or if there is already an-
other source of attenuation in front of the HP 83480/HP 83487A, or
• when you know there is no high frequency ringing associated with the device
under test and you want to use the high sensitivity of the HP 83487A.
The fiber-optic connectors on the 5 dB attenuator, like all fiber-optic
connectors, are easily damaged when connected to dirty or damaged cables
and accessories. Before making any connections to the attenuator,
"Cleaning Connections for Accurate Measurements" on page
Summary
The HP 83480A with the HP 83487A plug-in module was designed for high
sensitivity and has excellent waveform fidelity for signals with peak powers
less than 400 µW (–4 dBm). For signals with peak powers greater than 400 µW
(–4 dBm), a multimode attenuator is used to maintain high waveform fidelity.
By using the right attenuator, and entering the correct attenuation factor into
the external scale variable, the HP 83480A/HP 83487A makes true Fibre
Channel and Gigabit Ethernet compliance measurements throughout the
entire power range specified by the standards.
For more information, see Measuring High Power Waveforms with the
HP 83480/83487A, Product Note 83480-1. This is available through your local
HP sales office or at www.hp.com/go/lightwave.
Measuring High Power Waveforms
refer to
5-14.
Reference
5-9