Nautel NX300, Operation And Maintenance Manual

Page: 13 / 162

NX300 Operations and Maintenance Manual Description
Issue 3.0 2012-11-01 Page 1-5
RF power stage
See electrical schematics
SD-4
,
SD-5
and
SD-6
. The RF power stage includes all of the transmitter’s
10 kW RF power blocks. The NX300 contains 30 RF power blocks - ten in each of its three cabinets.
Each RF power block contains four RF power modules and associated relays, a fan tray, and
connections to the RF drive distribution PWB, PDM distribution PWB and rack interface PWB. Each
RF power module accepts RF drive, PDM and control voltages from the exciter stage. B+, +48 V
and +15 V dc voltages are input from the B+ distribution assembly and the rack interface PWB. The
output of each RF power module is applied to a primary winding of a series combining transformer.
The resultant combined output is applied to the RF output network.
To facilitate “on-air” servicing, each module has an associated relay that forces a contact closure
across the appropriate primary winding of the series combining transformer when an RF power
module is removed from the transmitter. When the transmitter is shut down, all relay contacts close,
isolating the RF power modules from the output network and improving their immunity to lightning.
RF output network
See electrical schematic
SD-5
and Figure 1.3 . The combined RF output is filtered through an RF
network consisting of two “T” networks with a shunt third harmonic trap, and then provided to the
antenna system. The RF output is monitored by an RF current probe, RF voltage probe and RF
sample probe. Samples from these probes are provided for control and monitoring purposes (see
“VSWR protection” on page 1-7 ).