HP 83487A User Manual page 76

Reference
Measuring High Power Waveforms
Table 5-1. Recommended Attenuation for Signals > –10 dBm with 100% Overshoot
Average Power
µ
dBm
W
100 –10.0
125 –9.0
200 –7.0
316 –5.0
400 –4.0
500 –3.0
800 –1.0
1000 0.0
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 µW), 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
5-8
100% Overshoot Attenuation
Peak Power (100%)
µ
dBm
W
400 –4.0
500 –3.0
800 –1.0
1265 1.0
1600 2.0
2000 3.0
3200 5.1
4000 6.0
Attenuator Net Input
Avg.
dB
dBm
0.0 –10.0
1.0 –10.0
3.0 –10.0
5.0 –10.0
6.0 –10.0
7.0 –10.0
9.1 –10.0
10.0 –10.0
Peak
dBm
–4.0
–4.0
–4.0
–4.0
–4.0
–4.0
–4.0
–4.0