Nautel VSHD Exciter, Инструкция по эксплуатации

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Page 3-2 VSHD Exciter Technical Instruction Manual
Issue 2.0 Section 3 Operation
3.1.1.1 AM-AM and AM-PM CORRECTION
When the transmitter is operating with digital carriers, the exciter linearizes the transmitter’s
RF drive signal by performing adaptive pre-correction. There are two correction parameters -
AM-AM Correction (see Figure 3-2) and AM-PM Correction (see Figure 3-3), which can be
viewed as instrument panels.
Figure 3-2: AM-AM Correction
AM-AM correction (see Figure 3-2): This panel displays the amplitude correction being
applied to the magnitude signal. The x-axis represents the signal amplitude and the y-axis
represents the gain correction applied for a given amplitude value.
The LUT curve can show that at low transmitter output power, more RF drive power is
required to correct for low final stage amplifier gain - the curve sharply increases as it drops
to 0 table value. (This low gain can also be overcome using additional bias, however pre-
correction is more efficient.) Equally, the curve could also increase sharply at the top end of
the table, suggesting that high RF drive power (gain) is required to connect for low gain at
final stage amplifiers (PA compression peak limiting). It is technically the inverse of the
transmitter’s power amplifier gain response.
Touch on the panel to display a cursor in the approximate area. The cursor position (gain and
Table index) is noted in the upper, right-hand corner of the panel. Touch in other areas of the
instrument to provide a coarse adjustment of the cursor position.
Use the left ( ◄ ) and right ( ►) arrow buttons as fine adjustments.
Use the up ( ▲ ) arrow button to maximize (if it was minimized) or the down ( ▼ ) arrow button
to minimize (if it was maximized) the panel size.