iDirect Evolution X1, Installation Manual, Page: 101 / 130

iDirect Satellite Router Installation and Commissioning Guide 85
iDX Release 3.3
15 1 dB Compression Point
and Maximum Power
This chapter describes how to determine the IF drive level that causes 1 dB gain compression
of the Block Up-Converter (BUC). This IF level is the “never exceed” level for driving the
particular BUC used. The chapter also contains an optional procedure to determine the
maximum power with a modulated carrier.
Note: The procedures in this section assume that the maximum power in the options
file that was loaded on the Satellite Router is set to the highest possible value.
If not, it may not be possible to determine the 1 dB compression point and
modulated maximum power.
This chapter includes the following sections:
• “Preparation” on page 85
• “Determining the 1 dB Compression Point” on page 87
• “Optional Procedure to Determine PN Max Power” on page 88
15.1 Preparation
Determination of the 1 dB compression point (P1dB) is made immediately following successful
cross-pol adjustment. The Satellite Router is transmitting a high-level continuous-wave (CW)
signal to the satellite, and the respective
Cross Polarization windows are open on the local
PC user interface. Under direction of the satellite access control center, the Satellite Router
transmit IF level is increased until BUC gain compression is detected.
To determine the 1 dB compression point, the access controller must carefully measure
incremental power changes at a high resolution. It may be necessary to perform the
procedure more than once to be certain that the 1 dB compression point has been properly
identified. Follow the direction of the access controller.
The 1 dB compression point is defined as the output power level at which BUC amplifier gain
has decreased by 1 dB from the small-signal value. If for example a particular amplifier
exhibits a low-power gain of 40 dB, the P1dB point is the output power level at which gain has
been reduced to 39 dB. See
Figure 49 for an illustration of the concept using sample data
representing a typical solid-state amplifier.
Although the P1dB point is located beyond the start of gain compression and is therefore in
the non-linear region of the transfer characteristic, most BUCs can operate safely at that
power level without exceeding the limits imposed by the transmit spectral mask. Many of