Maintenance—492/492P Service Vol. 1 (SN B030000 & up)
A = Center frequency tuning stub
B = Base-emitter voltage testpoint(TP1015)
C = Feedback adjustment tab (C1021)
D = Center frequency adjustment tab (C1022)
P220, 2182 MHz Unbuffered Output Port
P222, 2182 MHz Buffered Output Port
t
! I
<1^1 I
r f ; i
2182 MHz Microstrio Oscillator
P221, 100 MHz
Reference Input
0 dBm
2200 MHz Reference Mixer
· 2200 MHz Reference.
- 1 2 V
+ 12V
Supplies
2182 MHz Tune Input
18 MHz Difference
C2203
Frequency Out
C2204
+ 1 2 V Supply
Fig. 4-19. Adjustments and test point locations within the oscillator section.
a.
Check for OdBm ±3dB output power at the
unbuffered port, P220.
b.
Connect the test spectrum analyzer to P222, termi
nate P220, then check for an output level of +10 dBm
±3 dB from the buffered port.
4. Check the 2200 MHz Reference Mixer
a.
Use a probe, consisting of a short length of semi-rigid
coaxial cable with a dc block (see Fig. 4-20), to connect the
output of the reference mixer (C204) to the input of the test
spectrum analyzer. Ground the outershield of the coaxial
cable against the 2nd LO housing.
5. Check the Tune Range
a.
Adjust the variable supply to vary the voltage to the
2182 MHz tune line from 0 to -12 .5 V and note the fre
quency change at C2204 (output of the 2200 MHz Refer
ence Mixer).
b.
Frequency change or tune range should equal 20 to
35 MHz for a voltage change of 0 to —12.5 V on the tune
line.
6. Reassembly
a.
Disconnect and remove the connections from the vari
able power supply and the test spectrum analyzer.
b.
Confirm that the output signal frequency is 18 MHz,
±1 MHz. Adjust the tab (C1022) for the 2182 MHz
Microstrip Oscillator, to bring the 18 MHz within the 1 MHz
tolerance.
c.
Confirm that the output level of the 18 MHz signal is
approximately - 3 6 dBm. If the level is below —46 dBm,
check the signal levels from the 2200 MHz Reference Mixer
and the 2182 MHz Microstrip Oscillator (—28 dBm, ±8 dB
from the 2200 MHz Reference Mixer and + 8 dBm, ± 3 dB
from the oscillator).
REV JUN 1983
b.
Replace the lid for the oscillator housing and install
the 26 screws. Install the screws loosely, then tighten them
starting from the center of the lid and progress along the
edges toward the corners to insure that no gaps exist be
tween the lid and the housing. Any gaps will allow RF leak
age that can produce spurious responses.
c.
Reinstall the assembly on the RF deck. Remove the
50 Ω terminations and reconnect the cables. Use a 5/16 inch
open-end wrench to tighten the semi-rigid coaxial connec
tors to 8 to 10 inch-pounds.
4-29
