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RACAL RA6790/GM
ALIGNMENT AND TUNING MANUAL
From
[email protected]
February 2003
Racal RA6790/GM Alignment & Tuning Manual
CHAPTER 3
ASSEMBLED RECEIVER ALIGNMENT AND TEST
3-1. INTRODUCTION.
This chapter provides both alignment procedures and an end -to-end check for an
assembled Receiver. The information is presented in two sections with alignment
procedures contained in Section I and procedures for an end-to-end check
presented in Section II. The alignment procedures are designed to permit
alignment of any one or all of the various functions in the Receiver; however, the
adjustments in some functions interact with other functions so chat care must be
taken when any one function alone is aligned. The end-to-end checks are designed
to make sure that a Receiver is operational after assembly of new or repaired circuit
cards or modules.
SECTION I. ASSEMBLED RECEIVER ALIGNMENT
3-2. GENERAL.
The circuit card and module assemblies may be aligned and checked after they are
installed in a working Receiver. The following paragraphs provide detailed step-by-
step instructions for aligning the Receiver assemblies. The alignment procedures
require that external power be connected to the Receiver, the Receiver power
switch turned on and that the mode, bandwidth, AGC and frequency be set as
described in each procedure.
Refer to T.O. 31R2 -2URR-251 for location of circuit cards and adjustments.
a. Power Supply Assembly AlO.
The power supply used in the Receiver does not contain any adjustments or
controls other than the line voltage select card located in A10J1. If all voltages
checked correctly as specified in Section XI of Chapter 2, it can be assumed that
the power supply is functioning properly. If the power supply has not been tested
then the 3-1 voltage levels as spelled out in Chapter 2 should be checked before
performing any alignment procedures.
WARNING
The filter capacitors used in the power supply will retain an electrical charge after
power is removed.
The capacitors should be discharged slowly by shorting the terminals through a
protected resistive device. Disconnect the ac line cord from A10J1. Remove the
metal cover from the power supply and then reinsert line cord and turn Receiver
power on. Using the digital multimeter, check the voltages appearing on connector
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Racal RA6790/GM Alignment & Tuning Manual
A10A1 (refer to Table 2-28 in Chapter 2). Do not disconnect power output
connector J3 during these measurements, as this will unload the power supply and
could result in erroneous readings.
b. Low Pass Filter, Assembly Al.
Test equipment required to align the low pass filter Al is the Spectrum Analyzer
listed in Table 1-2.
(1) Connect the output of the Tracking Generator to the RF IN connector Jl of
the Receiver. Use 50-ohm cable.
(2) Connect the output cable (A1W2) to the input of the Spectrum Analyzer,
utilizing a 50-ohm cable.
(3) Set the Tracking Generator as follows:
Mode: Marker
Function: Track Analyzer
RF Output Level: 0 dBm
Marker Intensity: Maximum
Resolution: 1 kHz
(4) Set the Spectrum Analyzer as follows:
Scan Width: 0-100 Mhz
Input Attenuation: 20 dB
Scan Time: 20 Msec/Div.
Log. Ref. Level: 0 dBm, 10 dB Log
Video Filter: 10 kHz
Scan Mode: Internal
Scan Trigger: Auto
(5) Set the Marker to a frequency of 30 MHz.
(6) Observe trace and adjust LI for maximum amplitude at the marker frequency.
(7) Note response at 30 MHz and ensure that it is not more than 1.0 dB below
LOG REF line (see Figure 3 -1).
(8) Set marker to a frequency of 40.455 MHz. Adjust L3 for minimum amplitude
at the marker frequency.
(9) Set marker to a frequency of 43.19 MHz. Adjust L2 for minimum amplitude
at the marker frequency.
(10) Set marker to a frequency of 52.30 MHz. Adjust L4 for minimum amplitude
at the marker frequency.
(11) Compare spectrum analyzer trace with that depicted in Figure 3-1. The
shape and minimum trace points should closely approximate this shape. If
not, repeat the alignment procedures until the trace most nearly follows that
shown in the illustration.
(12) Disconnect the test equipment and reconnect cable A1W2 to J5 on the
chassis.
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Racal RA6790/GM Alignment & Tuning Manual
45 MHz RELATIVE LEV EL>20dB
0.5MHz 40.453MHz <^ EACH GRATICULE = 10 MHz
Figure 3-2. Alignment Waveforms
45 MHz RELATIVE LEVEL> 20dB
EACH GRATICULE lOdB
<^ EACH GRATICULE = 10 MHz
Figure 3-2. Alignment Waveforms
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Racal RA6790/GM Alignment & Tuning Manual
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: 28.24 MHz
Output Level: +10 dBm
Input Attenuator: 20 dB
Log Reference Level: +10 dBm, 10 dB Log
Bandwidth 300 kHz
Scanwidth: 1 MHz/Div
Scan Time: 20 Msec/Div
Video Filter: 10 kHz
(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; 0 dBm
Bandwidth: 100 kHz
Scanwidth: 2 MHz/Div
Input Attenuation: 10 dB
Scan Time: ^0 as
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Racal RA6790/GM Alignment & Tuning Manual
Log Ref. Level: -10 dBa
Log/Lin. Switch: -0 dB Log
(15) Adjust the tracking generator for 30 MHz and adjust coils Lll and L12 for-
peak response.
(16) Set tracking generator to sweep between 0 and 100 MHz. Check that all
frequencies above 56 MHz are at least 20 dB down from a reference level at
30 MHz.
(17) Disconnect the tracking generator from Pi and the spectrum analyzer from
E3-E5. Reconnect PI of cable W2 to Jl on A2.
(18) Connect the RF signal generator to PI of A2 and adjust for 2.0000 MHz at -
20 dBm. Adjust the Receiver frequency to 2.00000 MHz. AGC to MAN and
IF GAIN to maximum.
(19) Connect the spectrum analyzer, using the high impedance probe, to El on A3
(First IF output of A2). Set analyzer to display 40.455 MHz.
(20) Adjust transformer T3 for maximum output. Ensure that the output level is
not less than -17 dBm.
(21) Set the RF signal generator frequency to 10.000 MHz and adjust the
Receiver frequency to 10.00000 MHz.
(22) Ensure that the output level is not less than -17 dBm.
(23) Set the RF signal generator frequency to 29.999 MHz and adjust the
Receiver frequency to 29.99900 MHz.
(24) Ensure that the output level is not less than -17 dBm.
(25) Turn the Receiver off. Disconnect all test equipment and reconnect PI of
cable A2W1 to J5.
d. Second Mixer, Circuit Card Assembly A3.
The second mixer assembly A3 is located in the bottom portion of the Receiver.
The RF signal generator and RF millivoltmeter, listed in Table 1-2, are required to
align this assembly.
(1) Disconnect PI of cable A3W2 from J6, located on the Receiver chassis, and
connect PI to the RF mi Hi voltmeter with high impedance probe.
(2) Connect the RF signal generator to Jl-RF IN on Receiver rear panel.
(3) Turn the Receiver on and set the MODE to AM, any bandwidth, AGC to
manual and IF GAIN to the maximum clockwise position and Receiver
frequency to 1.5 MHz.
(4) Adjust the RF signal generator frequency to 1.5 MHz and the output level for
a RF millivoltmeter indication of -10 dBm.
(5) Adjust coils L8, L7, L6, L5 and Tl, in the order given, for peak output
indication on the RF millivoltmeter. Readjust the RF signal generator level as
required to maintain the -10 dBm output reference.
(6) After all coils have been adjusted for peak output, check the output level of
the RF signal generator. RF signal generator output level should not be
greater than -53 dBm. If gain is not correct adjust R26 (maintain -10 dBm
reference) and RF signal generator until gain is as specified. If R26 adjusts
to maximum and specified gain cannot be obtained, then slightly adjust C3
for peak output. Readjust R26 for specified gain.
(7) Turn the Receiver off and disconnect all test equipment. Reconnect PI of
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Racal RA6790/GM Alignment & Tuning Manual
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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Racal RA6790/GM Alignment & Tuning Manual
generator to .5 uV. Note reading of RF millivoltmeter.
Increase output of AM/FM signal generator +120 dB in 10 dB steps and
assure
that reading on RF millivoltmeter remains within 3 dB of that obtained at the
.5 uV RF input level.
(12) Remove the link between the filter input and output sockets and reinstalls the
filter previously removed. Determine the bandpass filters installed in the
Receiver.
(13) In order to examine the bandpass characteristics of the filters, the tracking
generator and spectrum analyzer must be used in the same manner as in
Step 4 above. Set the tracking generator/spectrum analyzer as follows:
Frequency: 455 kHz
TG Level: 40 dBm
Input Attenuation: 30
Log. Ref. Level: 0, 10 dB/Log.
Linear Sensitivity: Adjusted to set trace at 0 Log marker on display.
Scan Time: .5 Seconds
Scan Width/Div. See Chart Below
Bandwidth: See Chart Below
Video Filter: 10 Hz
(14) Ensure that the Receiver is in manual gain and that the IF Gain control is at
maximum CW rotation. Select each filter position via the MODE panel.
Observe the trace on the spectrum analyzer for each filter selected. It may
be necessary to adjust the IF gain control to avoid distortion of the IF
passband. Table 3-1 provides the passband maximum and minimum va lues
for the 3 dB and 60 dB points. Note that the Scan width and Bandwidth will
have to be adjusted to each filter as follows:
Filter B/W Scan Width/Div. Bandwidth
400 Hz 0.5 kHz 0.3 kHz
1000 Hz 0.5 kHz 0.3 kHz
1200 Hz 0.5 kHz 0.3 kHz
2.0 kHz 1.0 kHz 1.0 kHz
3.0 kHz 1.0 kHz 1.0 kHz
3.2 kHz 1.0 kHz 1.0 kHz
6.8 kHz 2.0 kHz 1.0 kHz
16 kHz 5.0 kHz 3.0 kHz
USB/LSB 1.0 kHz 1.0 kHz
(15) If the A5 ISB option is installed, the LSB filter must be checked by using the
HI-Z probe on TP7 of the A5 board. Ensure that the Receiver is in the LSB
mode.
(16) Disconnect all test equipment. Restore cable W1P1J6 to coaxial fitting J6
on the chassis.
(17) Connect AM/FM signal generator to the Receiver RF input jack Jl. Attach the
junction box to connector J3, AF OUT, on the rear of the Receiver. Connect
the input of the distortion analyzer to the BNC connector labeled "MONITOR"
on the junction box. Set the distortion analyzer Function Switch to Voltmeter
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Racal RA6790/GM Alignment & Tuning Manual
and the Meter Range to +10 dB (1 mW).
(18) Select the FM mode, adjust the AM/FM signal generator frequency for 1.5
MHz with an output of -40 dBm and modulate the signal at 1 kHz
with a peak deviation of +4 kHz. Check the audio output indication on the
distortion analyzer meter. Adjust coil L3 for peak audio output.
(19) Turn Receiver off. Disconnect all test equipment and replace filter assembly
cover.
f. ISB IF/AF, Circuit Card Assembly A5.
This circuit card is an optional assembly and may not be present in all Receivers. If
it is used, the A5 assembly is ins talled in the top portion of the Receiver, towards
the rear. The test equipment required to align the A5 module includes the spectrum
analyzer, AM/FM signal generator, digital multimeter, and RF Millivoltmeter,
shown in Table 1-2.
NOTE
The LK 1 link on the A4 circuit card must be ins talled for ISB operation and the
alignment procedures for A4 must be performed prior to any adjustment on the A5
circuit card.
(1) Connect the AM/FM signal generator to Jl-RF IN on the rear
panel. Turn the Receiver on and adjust frequency to 1.5000 MHz, AGC to
MAN, IF gain to maximum and mode to LSB.
(2) Connect the high impedance test probe of the RF millivolt-
meter to TP7 on circuit card A5. Set the AM/FM signal generator to 1.4982
MHz at an output level of 30 uVolts (-73 dBm).
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Racal RA6790/GM Alignment & Tuning Manual
TABLE 3-1. BANDPASS FILTER CHARACTERISTICS
Bandpass Filter Pas sband - Hz Stopband - Hz
*3 dB Maximum Attenuation 60 dB Minimum Attenuation
From To Below Above
400 Hz -200 +200 -1240 +1240
1.2 kHz -600 +600 -3600 +3600
6.8 kHz -3400 +3400 -1120 +12000
LSB +350 +3050 -300 +4000
USB -350 -3050 -4000 +300
400 Hz -200 +200 -500 +500
(Defined delay) -600 +600 -1500 +1500
1.2 kHz
(Defined delay) -600 +600 -1500 +1500
1.2 kHz
(Defined delay) -1620 +1620 -2150 +2150
3.24 kHz
(Defined delay) -3400 +3400 -6800 +6800
6.8 kHz
(Defined delay) -8000* +8000* -16000 +16000
16.0 kHz
(Defined delay) -250 +250 -1500 +1500
500 kHz
(Linear phase) -500 +500 -3000 +3000
1.0 kHz
(Linear phase) -1000 +1000 -6000 +6000
2.0 kHz
(Linear phase) -1500 +1500 -9000 +9000
3.0 kHz
(Linear phase) -3000 +3000 -18000 +18000
6.0 kHz
NOTES:
*16.0 kHz (defined delay) filter shall be 2 dB maximum attenuation. LSB
filter should be monitored at TP7 on A5 board if this board is installed.
Page 10 of 20
Racal RA6790/GM Alignment & Tuning Manual
(3) Adjust R19 and R23 to the full clockwise positions. Cancel MAN AGC and
note the indication of the RF millivoltmeter. RF millivoltmeter should read 70
+10 millivolts.
(4) Reduce the AM/FM signal generator output to -113 dBm (0.5 uVolts). Select
MAN AGC, cancel SHORT AGC, adjust R19 for 64 +10 millivolts indication
on RF millivoltmeter.
(5) Connect the digital multimeter to TP9 on A5. Cancel MAN AGC, select
SHORT AGC. Increase AM/FM signal generator output to -78 dBm (30
uVolts). Set R23 for an indication of 8.5 +0.05 Volts dc on the digital
multimeter.
(6) Disconnect the AM/FM signal generator from Jl-RF IN, the digital multimeter
from TP9 and the RF millivoltmeter from TP7.
(7) Disconnect PI of cable Wll from J3 and A4. Connect the tracking generator
to Jl and connect the spectrum analyzer to TP7 on A5, using the high Z
probe. Adjust the spectrum analyzer as follows:
Output Level: -54 dBm (tracking generator)
Center Frequency: 455 kHz
Input Attenuation: 10 dB
Sweep Width: 20 kHz/div.
Bandwidth: 3 kHz/div.
Log Ref. Level: 0 dBm
Log/Lin Switch: 10 dB Log
(8) Set AGC to MAN and the IF GAIN control for approximately -6 dBm on the
spectrum analyzer. While observing the spectrum analyzer trace, adjust LI
and L2 to obtain the bandpass waveform shown for Step 12 of the L4
adjustment procedures in Paragraph e. If a double peak is obtained the
trough should be no greater than 0.5 dB below the peaks.
(9) Disconnect the tracking generator from Jl and reconnect P2 of cable Wll to
J3 on A4. Disconnect PI of cable Wl from J7 on chassis (output of A3) and
connect the tracking generator to PI.
(10) With the tracking generator/spectrum analyzer controls adjusted as
described in Step 7 and the LSB mode selected on the Receiver, adjust the
IF GAIN control for approximately -6 dBm. Refer to Table 3-1 for the LSB
filter passband and stopband characteristics and ensure that the spectrum
analyzer trace display meets those characteristics.
(11) Turn the Receiver off. Disconnect the tracking generator from PI and
reconnect PI of cable Wl to J7 on chassis. Disconnect the spectrum analyzer
from TP7.
g. Remote Interface and Microprocessor, Circuit Card Assemblies A6A1
and A6A2.
The remote interface card (A6A1) is an optional assembly and may
or may not be installed in the Receiver. When it is used, both the A6A1 and
A6A2 cards are mounted on the right hand side of the top portion of the
Receiver. These two circuit cards do not contain any variable components
and therefore do not require any alignment or adjustment.
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Racal RA6790/GM Alignment & Tuning Manual
h. First LO Synthesizer, Circuit Card Assembly A7.
This circuit card assembly is located in the bottom portion of the Receiver. The test
equipment required to align the assembly includes the spectrum analyzer, digital
multimeter, digital frequency counter and 50-ohm adapter, listed in Table 1-2.
(1) Connect the digital multimeter between TP5 and ground on the A7 circuit
card assembly. Set R16 for a digital multimeter indication of 5.2 +0.01 Volts
dc.
(2) Disconnect PI of cable W2 from Jl on A2. Connect the spectrum analyzer to
PI (1st LO output) using 50-ohm adapter.
(3) Set receiver frequency to 1.046 MHz and adjust the spectrum analyzer to
observe 1 kHz sidebands on the 41.501 MHz output at a nominal +9 dBm
level.
(4) Adjust R5 for the best rejection of "the 1 kHz sidebands. A sideband
rejection of 55 dB or more is acceptable.
(5) Disconnect the spectrum analyzer from Fl and connect the digital frequency
counter to this point. Tune the Receiver over its entire range (0.5 to 30 MHz)
and note that the digital frequency counter tracks 40.455000 MHz abve the
Receiver freqency + instrument error.
(6) Turn the Receiver off. Disconnect the digital frequency counter from J4 and
reconnect PI of cable W2 to Jl on A2. Disconnect the digital multimeter from
TP5.
i. Second LO/BFO Synthesizer, Circuit Card Assembly A8.
This circuit card assembly is located in the bottom portion of the Receiver. The test
equipment required to align this assembly includes the 50-ohm adapter, digital
multimeter, RF millivoltmeter and the digital frequency counter, listed in Table 1-2.
(1) Check the links LK1 and LK2 on circuit card A8 and verify that
they are connected as required for the reference frequency IN/OUT mode of
operation. The links should be made as follows:
1 MHz - Links LK1 and LK2 linked.
5 MHz - Link LK1 open, LK2 linked.
10 MHz - Link LK1 linked, LK2 open.
(2) Make sure the REF-INT/EXT switch S2, on the rear panel, is set to the INT
position.
(3) Disconnect PI of cable W4 from J2 on A3. Connect the digital frequency
counter to Pi (2nd LO output). Connect the digital multimeter between TP5
and ground. Set the digital multimeter to the 10 Volt dc range.
(4) Turn the Receiver on. Digital multimeter should read between 3 to 8 volts dc
(not adjustable). Digital frequency counter should read 40 MHz +20 Hz.
(5) Disconnect the digital frequency counter from PI and connect the RF
millivoltmeter with the 50-ohm adapter to PI. RF millivoltmeter should read 0
dBm +2 dB. If reading is not within the limits adjust L9 and L10 for maximum
output. Recheck RF millivoltmeter for correct indication.
(6) Disconnect the RF millivoltmeter from PI and reconnect PI of cable W4 to J2
on A3. Disconnect the digital multimeter from TP5.
(7) Set the Receiver MODE to CW and the BFO to center.
(8) Disconnect P2 of cable W6 from J5 on A4 and connect the digital frequency
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Racal RA6790/GM Alignment & Tuning Manual
counter to P2 (BFO output). Connect the digital multimeter between TP8,
and ground and set on the 10 Volt dc range.
NOTE
With the probe of the digital multimeter on TP8 a FAULT may be indicated on
the front panel. This is normal and alignment procedures should be
continued with the FAULT indicator on. FAULT indication should extinguish
when the digital multimeter probe is removed.
(9) The digital frequency counter should indicate 455,000 +1 Hz. Digital
multimeter should indicate between 4.5 and 7 Volts dc. If correct digital
multimeter reading is not obtained, adjust coil L4 for correct indication on
digital frequency counter.
(10) Select BFO variable on the Receiver and tune the BFO over its entire range
(-8 to +8 kHz) while observing the Receiver front panel BFO and digital
frequency counter indications. Digital frequency counter should
track 455,000 Hz above the Receiver BFO indicated frequency. Also
observe
the digital multimeter indication while tuning the BFO. Digital multimeter
should not deviate more than +1.5 Volts from reading obtained in Step 9 at
BFO center.
(11) Disconnect the digital frequency counter from P2 and reconnect P2 of cable
W6 to J5 on A4. Disconnect the digital multimeter from TP8.
(12) Disconnect PI of cable W3 from J2 on A7. Connect the digital frequency
counter and oscilloscope to PI. Ensure that the frequency is 1 MHz +0.5 Hz,
and the output level is switching between approximately 0 and +5 Volts
(TTL).
(13) Turn the Receiver off. Disconnect digital frequency counter and oscilloscope
from PI and reconnect PI of cable W3 to J2 on A7.
j. Front Panel Interface, Circuit Card Assembly A9.
This circuit card does not contain any variable components, and therefore does not
require any alignment or adjustment procedures.
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Racal RA6790/GM Alignment & Tuning Manual
SECTION II. ASSEMBLED RECEIVER TEST
3-3. GENERAL.
This section provides procedures to check the Receiver's operation after repairs
and/or alignment have been made. The test procedures are designed to provide an
overall operational check of the Receiver and to ascertain that its functional
capabilities have not been impaired.
These tests determine power supply operation, synthesizer performance,
reference frequency accuracy, audio power and distortion, gain modes and final IF
frequency. Before the tests are conducted all repairs and reassembly should be
inspected for quality workmanship and completeness. All shields and covers should
be in place and the Receiver allowed to warm up for at least 30 minutes.
a. Power Check.
(1) Make sure that circuit card switch is installed correctly and proper fuse is
installed for the line voltage to be used.
(2) Connect the power cord to the Receiver then to the power source. Set REF
IN/OUT switch on rear panel to INT.
(3) Turn Receiver POWER switch to on and note that there is a random display
of information on the two front panel LCD's.
(4) Make sure that all LCD back lighting lamps are on.
(5) Make sure that the FAULT indicator is off. If this indicator is on refer to
Receiver manual 31R2-2URR-251 for information on clearing the fault.
(6) Perform BITE check as outlined in Receiver manual 31R2 -2URR-251,
b. Frequency Tuning and Display.
(1) Press ENTER then press numeral keys 0, 0, 5. 0, 0, 0, O and O and note
that 0.500000 MHz is displayed.
(2) Press ENTER then press numeral keys 1, 5, 0, 0, 0, 0, 0 and 0 and note that
15.000000 MHz is displayed.
(3) Press TUNE RATE pus hbutton until there is no indication under tuning.
(4) Rotate tuning knob both clockwise and counterclockwise and note frequency
displayed slowly increases with clockwise rotation and decreases with
counterclockwise rotation at a 1 Hz per step rate.
(5) Select both SLOW and FAST tuning rates repeating step (4) for each tuning
rate; SLOW changed at a 30 Hz rate, FAST at a 1 kHz rate.
(6) Press the LOCK pushbutton then rotate the tuning knob and note that there
is no frequency change.
(7) Press ENTER then press numeral keys 2 and 9 and note that frequency
displayed is 29.000000 MHz.
c. Frequency Calibration Resolution.
This test requires the digital frequency counter listed in Table 1-2.
(1) Disconnect PI of cable W4 from J2 and A3 and using the cable coupler
connect the digital frequency counter to PI on cable W4.
(2) Ensure that the frequency is 40 MHz j^8 Hz. This ensures that the internal
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Racal RA6790/GM Alignment & Tuning Manual
standard is 5 MHz +1 Hz.
(3) Disconnect digital frequency counter and reconnect PI of cable W4 to J2 and
A3.
d. RF Gain Control.
This test requires the distortion analyzer and RF signal generator listed in Table 1-2.
(1) Using a 600 ohm termination connect distortion analyzer to AF LINE output.
(2) Set the Receiver controls as follows:
Power ON
Gain Mode Manual
Detection Mode CW
BW 3.24 kHz (or closest bandwidth available)
(3) Set the RF signal generator for an output of 1.5 MHz at ◦ Jabse Service Manual Search 2024 ◦ Jabse Pravopis ◦ onTap.bg ◦ Other service manual resources online : Fixya ◦ eServiceinfo