Nautel VS1 - RF Signal Path

VS1 Operations and Maintenance Manual Description
Page 1-4 Issue 3.1 2013-10-01
• provides local and remote interfacing for the transmitter. Local interfacing is performed via
the front panel display (U4) - a 4 x 20 character LCD display - and its adjacent keypad. The
UI contains a menu-based series of pages that serve specific functions. Similar interfacing, as
well as more advanced functionality, is available on a remotely accessed AUI.
Except for the RF drive signal, all signals going between the exciter, RF drive and RF power stages are
passed through the interface PWB (A3).
RF drive stage
See also electrical schematics Figure SD-2 and SD-4.
The RF drive stage is comprised of exciter circuitry within the exciter/control PWB (A1), the pre-
amp/IPA PWB (A5) and the splitter PWB (A4).
The pre-amp/IPA PWB accepts the low level RF Drive output from the exciter/control PWB (A1).
Its RF output is generated by the Pre-Amp V input (set at +48 V) and IPA V input (set at +48 V), as
well as the and Pre-Amp Bias output and IPA Bias output from the exciter/control PWB (A1). The RF
output level is controlled by the RF input level, generated by the exciter/control PWB. The output of
the pre-amp/IPA PWB (nominal 75W) is applied to a directional coupler on the combiner PWB
(A10), which monitors this output level. The directional coupler’s sample is applied to the combiner
interface PWB (A12). The IPA output is then applied to the input of the splitter PWB (A4). The
splitter PWB splits the RF drive signal into four outputs, which are applied to the RF power stage’s
PA PWBs (A6 through A9). Cooling air for the pre-amp PWB is provided by fan B1.
RF power stage
See also electrical schematics Figure SD-2 and SD-5.
The RF power stage accepts the intermediate RF drive signal from the RF drive stage and generates
the final RF output. It consists of four PA (power amplifier) PWBs (A6 through A9), the combiner
PWB (A10), the low pass filter PWB (A11), and the combiner interface PWB (A12).
PA PWB
See Figure SD-5. Each PA PWB (A6 through A9) is a push-pull RF power amplifier. It is capable of
providing 350 W of RF power in the FM broadcast band (87.5 to 108.0 MHz). The RF output is
controlled by the PA V level generated by the power supply module, and the PA Bias output from the
exciter/control PWB (A1). The RF output of each PA PWB is applied to an input of the combiner
PWB. Cooling air for the PA PWB is provided by fans B1, B2 and B3.