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c.
First Mixer, Circuit Card Assembly A2.
The first mixer assembly A2 is located in the bottom portion of the Receiver. The
spectrum analyzer, RF signal generator, RF millivoltmeter and digital multimeter,
listed in Table 1-2, are required to align the first mixer assembly A2.
(1)
Utilizing cable W2, connect the output of the tracking generator to Jl on A2
board.
(2)
Connect the spectrum analyzer via the high impedance probe to TP2 of A2
and set the spectrum analyzer as follows:
Center Frequency:
Output Level:
Input Attenuator:
Log Reference Level: +10 dBm, 10 dB Log
Bandwidth
Scanwidth:
Scan Time:
Video Filter:
(3)
Set Receiver mode to AM, 3.2 kHz Bandwidth, AGC to Manual and IF GAIN
control to maximum clockwise position.
(4)
Adjust LI for a notch (minimum amplitude) at 28.24 MHz.
(5)
Set analyzer center frequency to 38.23 MHz. Adjust L4 for notch.
(6)
Set analyzer center frequency to 40.38 MHz. Adjust L2 for notch.
(7)
Set analyzer center frequency to 40.455 MHz. Adjust L3 for notch.
(8)
Check filter passband level from 45 to 70 MHz. Ensure that this level is
greater than +9 dBm.
(9)
Check relative level at 41 MHz compared to level at 45 MHz. If relative level
is greater than 10 dB below 45 MHz level, adjust L3 slightly (one-quarter turn
or less) until 41 MHz level is only 10 dB below 45 MHz level.
(10)
Set spectrum analyzer for 0-100 MHz scan-width. Check relative level from
0.5 to 40.455 MHz compared to level at 45 MHz. Ensure this level is at least
20 dB lower (see Figure 3 -2A).
(11)
Disconnect tracking generator then connect the digital multimeter between
the collectors of Q3 or Q4 and ground. Set the digital multimeter to the 200-
uVolt dc scale.
(12)
Adjust R9 for 0 Volt reading. Disconnect digital multimeter from Q3-Q4 and
ground. Reconnect P2 of cable W2 to J4 on circuit card A7.
(13)
Disconnect PI of cable W2 from Jl on A2 circuit card and PI of cable A2W1
from J5 on chassis then connect the tracking generator to PI (RF input to
A2).
(14)
Connect the spectrum analyzer, using the high impedance probe, to the links
between E3 and E5. Set the spectrum analyzer controls as follows:
Output Level;
Bandwidth:
Scanwidth:
Input Attenuation:
Scan Time:
Racal RA6790/GM Alignment & Tuning Manual
28.24 MHz
+10 dBm
20 dB
300 kHz
1 MHz/Div
20 Msec/Div
10 kHz
0 dBm
100 kHz
2 MHz/Div
10 dB
^0 as
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