Terrasat IBUC - Power Measurement

IBUC Operation Manual 6-36
Terrasat Communications, Inc.
Rev. A
Power Measurement
The Terrasat IBUC is capable of accurately reading the input and output power for a
single carrier in either Continuous Signal Mode (CSM) or Burst mode. The dynamic
range for the input power is from -60 to -15 dBm and for the output power is from rated
power to 20dB below rated power. Each unit is loaded with a detector calibration lookup
table that compensates for detector variations in frequency, power level and
temperature. The reported power level is then based on the user-requested frequency
and the internal monitored temperature and power level. If multiple carriers are present
the composite transmit power level is read but accuracy is dependent upon actual
carrier frequencies, levels and modulation being used.
The power measurement is done in two ways:
1) Burst Mode
- In the Burst power measurement mode it is assumed that in normal operation
a transmit carrier may or not be present due to the nature of Burst mode
operation. Since the transmit burst pulse has a rise time and a fall time the
power must be reported as an average value. To maintain detected accuracy
of the burst pulse, 16 consecutive measurements of the pulse are taken (all
values below the power threshold setting are ignored). The 8 lowest values
are then dropped and the remaining 8 values averaged. The memory is then
automatically updated and the value is ready to be reported. Refer to Figure
6-10.
- Burst Time: 500us to 1s
- Measurement accuracy: +/- 2 dB absolute, 1.5dB p-p relative. Accuracy is
improved as the detected burst threshold level is raised closer to the carrier
peak.
- The detector accuracy is based on a pulsed unmodulated signal with a pulse
width of 500us.
2) Continuous Signal Mode (CSM)
- In the CSM power measurement mode it is assumed that in normal operation
a transmit carrier is always present. Therefore, reported power is the actual
measured power at the time of query.
- Measurement accuracy: +/- 1 dB absolute, 1 dB p-p relative*
- The detector accuracy is based on a CW unmodulated carrier.
* Relative measurement accuracy defines the error between any two power readings at
any particular frequency over the dynamic range.