Nautel NV7.5, Operation And Maintenance Manual

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NV10/NV7.5 Operations and Maintenance Manual Description
Issue 3.4 2016-08-03 Page 1-5
Exciters A (A3) and B (A4) are the RF drive sources for the transmitter. They accept the
external audio program and/or IBOC information (see the NV10/NV7.5 Installation Manual
for details on various program input types). The exciters’ main/standby operation is controlled
locally using the AUI, or remotely. The exciter outputs are applied to the RF drive splitter/
changeover assembly (A5). The exciter provides an RF drive signal of 25 W (in analog mode).
RF drive splitter/changeover assembly
The RF drive splitter/changeover assembly (A5) controls the routing of the main and standby
exciters and provides the RF drive signals for the four RF power modules. The assembly is
comprised of the splitter/changeover PWB (A5A1) and the 4-way RF drive splitter/attenuator
PWB (A5A2).
Exciter relay control
The RF drive outputs from exciters A and B are applied to the splitter/changeover PWB
(A5A1) at A5A1J1 and A5A1J2 respectively. The Exciter Relay Control input (A5A1J3-4) is a
signal applied from the control/monitor stage that controls relay A5A1K1.
• When exciter A is selected as the main RF drive source, the Exciter Relay Control input
is open circuit and relay A5A1K1 will be de-energized. Exciter A's output will be
applied to 3 dB hybrid coupler A5A1U1.
• When exciter B is selected as the main RF drive source, the Exciter Relay Control input
is near ground potential (0 V) and relay A5A1K1 will be energized. Exciter B's output
will be applied to 3 dB hybrid coupler A5A1U1.
Exciter drive splitter
The splitter/changeover PWB’s 3 dB hybrid coupler (A5A1U1) is connected as a splitter. The
RF drive source (A or B) selected by relay A5A1K1 is applied to A5A1U1’s input. The signal is
split into two equal amplitude signals that are 90° out-of-phase. These split signals are applied
to 4-way RF drive splitter PWB A5A2.
4-way RF drive splitter/attenuator
The 4-way RF drive splitter/attenuator PWB (A5A2) accepts the outputs from the splitter/
changeover PWB’s 3 dB hybrid coupler and splits it into four equal amplitude signals, using
two 3 dB couplers identical to A5A1U1. The outputs of the 3 dB couplers are applied to
attenuators for application to the four RF power modules. Attenuation values are set in order
to balance the RF drive output levels.