Nautel XR6, Troubleshooting Manual, Page: 74 / 291

XR6/XR3 Troubleshooting Manual Detailed Circuit Descriptions
Page 2-6 Issue 3.0 2009-07-15
Virtual capacitor
Complementary transistor pair U13:A and U13:B, capacitors C50 through C53 and associated
components form a virtual capacitor, the value of which is determined by current flow through
U13:A. Amplitude and phase of the
IPM compensation input controls gain of U13:A, thereby
controlling current flow in the transistor and ultimately the virtual capacitance of the IPM correction
circuit.
IPM BAL
ance potentiometer (R41) is adjusted, when the RF synthesizer PWB is in a
transmitter, for optimum correction of any incidental phase modulation.
Switch elements S6:1, S6:2 and S6:3 provide the proper capacitance depending on the carrier fre-
quency. See the table below to determine the settings for the switch elements.
IPM correction enable
The position of switch element S6:4 determines when the IPM correction circuit is enabled or disabled.
The IPM correction circuit should be disabled (switch S6:4 set to
CLOSED
position) when used in an
XR6/XR3 transmitter.
Waveform symmetry
RF DRIVE SYMMETRY
potentiometer R32 - which allows for minimizing of second harmonic levels -
is adjusted for an RF drive output waveform which is a symmetrical square wave (50% duty cycle), as
measured at the
RF DRIVE (TEST)
output (J5) of the RF drive buffer PWB. The position of
SYMMETRY ADJ
ust shorting jumper E6 determines when the RF drive symmetry circuit is enabled or
disabled. E6 should be installed in the
ENABLE
position (shorting pins 1 and 2) when used in an
XR6/XR3 transmitter.
f
c
(kHz)
Capacitance (pF)
S6 Switch Settings
1 2 3
190 - 589 48 1 1 1
590 - 879 36 1 1 0
880 - 1324 24 1 0 0
1325 - 1800 12 0 0 0
0 = switch open; 1 = switch closed
Note:
It may be desirable to disable the IPM correction circuit for some testing purposes. Return the
switch to its regular position during normal operation.