HP 83487A, Руководство пользователя, Страница: 76 / 98

5-8
Reference
Measuring High Power Waveforms
In order to find out if your device under test may be exceeding the input
power requirements for the HP 83487A, first measure the average power with
the internal power meter, and then measure the peak power on the eye dia-
gram. If the average power exceeds –10 dBm (100
µ
W), you may need to
attenuate the signal (this assumes there is 100% overshoot present). Insert
the recommended attenuation from Table 5-1, and then measure the average
power again. If you are using a laboratory attenuator, then you will have a dig-
ital readout of the attenuation. If you are using a simple fixed attenuator, then
the attenuation value will be the difference between the average power read-
ing with and without the attenuator.
The HP 83480A allows the attenuation to be accounted for and removed from
the measurement. Press the
Optical Channel Setup
key (above the optical con-
nector), and then the
External scale
softkey. Enter in the value of the attenuator,
and the instrument will then read the true signal level prior to attenuation.
You can then go back and measure the peak power on the eye diagram again. If
this measurement is the same as the original peak measurement without the
attenuator, then you do not have compression and you are in a safe measure-
ment power zone with or without the attenuator. If the peak measurement was
Table 5-1. Recommended Attenuation for Signals > –10 dBm with 100% Overshoot
100% Overshoot Attenuation
Average Power Peak Power (100%) Attenuator Net Input
µ
W dBm
µ
W dBm dB
Avg.
dBm Peak
dBm
100 –10.0 400 –4.0 0.0 –10.0 –4.0
125 –9.0 500 –3.0 1.0 –10.0 –4.0
200 –7.0 800 –1.0 3.0 –10.0 –4.0
316 –5.0 1265 1.0 5.0 –10.0 –4.0
400 –4.0 1600 2.0 6.0 –10.0 –4.0
500 –3.0 2000 3.0 7.0 –10.0 –4.0
800 –1.0 3200 5.1 9.1 –10.0 –4.0
1000 0.0 4000 6.0 10.0 –10.0 –4.0