Terrasat IBUC 3, Operation Manual

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Power Measurement
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5-11
Engineered to Endure
1. Burst Mode
In 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 and the envelope level
varies during symbol transitions when the signal is modulated, the power must be
reported as a peak value. To maintain detected accuracy of the burst pulse, 128
consecutive measurements of the pulse are taken. Once the initial reading exceeds
the burst threshold, 128 consecutive readings are taken (regardless of level). The
highest value of the 128 is displayed. The IBUC reports the most recent valid
reading above the burst threshold.
Burst Time: 500 µs to 1 s
Measurement accuracy: ±2 dB absolute, 1.5 dB p-p relative. Accuracy is improved
as the burst threshold setting is raised closer to the carrier peak.The detector
accuracy is based on a pulsed unmodulated signal with a pulse width of 500 µs.
2. Continuous Signal Mode (CSM)
In CSM power measurement mode, it is assumed that, in normal operation, a
transmit carrier is always present. Therefore, reported power is the peak power
over 128 consecutive readings.
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.
Notes:
To make the given accuracy achievable, the operating transmit frequency
information must be provided via M&C in order to use the information in the
detector’s internal calibration look-up table.
By default, the unit will be set to perform CSM measurements.
Input Power Overdrive Protection
To ensure that output stage transistors achieve saturation, and thus, maximum
performance, the IBUC
3
and IBUC
3
G
allow for input overdrive. The Input
overdrive point allows for 6 dB overdrive at 0 dB attenuation in Gallium Nitride FET
(GaN) based units and 2dB overdrive at 0dB attenuation in Gallium Arsenide (GaAs)
based units. As excessive saturation could diminish signal integrity and damage the
device due to unsustainable heat levels, a input overdrive protection algorithm is
employed to protect power amplifiers.
Such algorithm takes advantage of the IBUCs input and output power readings to
drive internal attenuators, changing input drive level to achieve protection. Input
overdrive protection depends on the selected operation mode. The three possible
operations modes are: Open Loop, AGC, ALC.