Nautel XR12, Troubleshooting Manual, Page: 76 / 283

XR12 Troubleshooting Manual Detailed Circuit Descriptions
Page 2-8 Issue 3.0 2009-07-28
- E1 in
INT
position (pins 2 and 3 shorted)
- E2 in
INT
position (pins 2 and 3 shorted)
- E4 in
EXT
position (pins 1 and 2 shorted)
The applied RF must be precisely the carrier frequency (f
c
) and its peak-to-peak voltage (sine or
square wave) must be between 5.0 V and 12.0 V.
External 10 mhz source
An external 10 MHz can be used for synchronization (i.e., GPS lock). When an external 10 MHz
signal is to be used as the RF drive source, the shorting shunt posts must be configured as follows:
- E1 in
EXT
position (pins 1 and 2 shorted)
- E2 in
EXT
position (pins 1 and 2 shorted)
- E4 in
INT
position (pins 2 and 3 shorted)
The applied RF must be precisely 10.00 MHz and its peak-to-peak voltage (sine or square wave)
must be between 2.2 V and 8.0 V
Interphase PDM driver PWB ( NAPM10B )
See electrical schematic Figure SD-14.
Carrier level control
The carrier level control circuit consists of U6, U2A, U2D, U3B, U3D, and their associated
components. U6 is a four-quadrant analog multiplier connected as a variable gain, wide-band, linear
amplifier. The modulation reference (
I1 ) input is multiplied by a factor determined by the level of the
carrier ref ( I2 ) and B+ ref ( I4 ) inputs to determine the gain and, in turn, the I3 output.
When there is no unbalanced audio input at J1-15, U2D's output (TP6), which is the modulation
reference, will be a nominal 1.4 V. When a pure audio sine wave is present at a level that will produce
100% modulation, the output of U2D will be a sine wave varying from 0 V to 2.8 V. The resulting
current flow through R12 is U6's
I1 input.