Racal RA6790/GM Alignment & Tuning Manual
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cable A3W2 to J6.
e.
Main IF /AF, Circuit Card Assembly A4.
This assembly is located in the top portion of the Receiver. The test equipment
required to align the assembly includes the spectrum analyzer, AM/FM signal
generator, digital
multimeter, RF millivoltmeter, junction box, distortion analyzer, and the 50-ohm
adapter, listed in Table 1 -2.
(1)
Remove the cover from the filter assembly. Verify that a 4 kHz (or less)
symmetrical filter is installed in the Receiver. Turn the Receiver ON and
initialize the Receiver (if necessary) by running the automatic BITE
sequence. Set the Receiver frequency to 1.500000 MHz, select the 4 kHz
(or less) filter, the AGC SHORT mode, and the AM operating mode.
(2)
Locate the coaxial cable connecting the A3 board output to
the A4 input (cable will be labeled W1P1J6 at the A3 end). Connect the
output of the tracking generator to the miniature cable connector W1P1.
This connection will inject the signal into A4J1. Connect the input of the
spectrum analyzer to J2, IF OUT, located on the rear of the receiver. Set
the tracking generator/spectrum analyzer controls as follows:
Output Level:
-50 dBm
Center Frequency:
455 kHz
Input Attenuation:
10 dB
Scan Width/Div.:
20 kHz
Scan Time:
0.1 Second
Log Ref.:
0 dB, 10 dB/Log
Video Filter:
100 Hz
(3)
Remove a filter and connect a link between the filter input and output
sockets. Select this filter position, set AGC to MAN and the IF GAIN control
to the maximum clockwise position.
(4)
While observing the analyzer trace adjust LI and L2 to obtain the bandpass
waveform as shown in Figure 3-2B. Adjust the IF Gain control to maintain a
peak indication of -4 to -6 dB on the spectrum analyzer display. If a double
peak is obtained the trough must be no greater than 0.5 dB below the peaks.
(5)
Connect AM/FM signal generator with 50-ohm cable to Receiver antenna
input (Jl-RF IN). Set AM/FM signal generator to 0.5 mv (-113 dBm).
Connect RF millivoltmeter to J2-IF OUT.
(6)
Set R39 and R1L9 to mid-range. Set R47 fully CCW. Set R105 fully CW.
Connect digital multimeter to TP9.
(7)
Set AM/FM signal generator and Receiver to 1.55 MHz. Select manual gain.
Set IF Gain to maximum. Adjust R39 for -10 dBm on RF millivoltmeter.
(8)
Select AGC SHORT. Set AM/FM signal generator to -80 dBm (22.5 mv).
Adjust R47 for 8.5 +.05 VDC on digital multimeter.
(9)
Select manual GAIN. Adjust IF GAIN control for 8.5+0.05 VDC on digital
multimeter. Adjust R105 for an increase of 1 dB on RF millivoltmeter.
(10)
Select AGC SHORT. Remove RF signal. Set R119 for 10 j^.Ol VDC on
digital multimeter.
(11)
Connect AM/FM signal generator to Jl-RF IN. Set output of AM/FM signal
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Page 300: ...RACAL RA6790 GM ALIGNMENT AND TUNING MANUAL From Maxhdrm2 comcast net February 2003...
