If the biasing for the amplifiers is not within the proper
operating range, the fault detector circuit will pull the FLAG
0 line low. This turns off Q5 causing Q6 to conduct. Q6 now
provides a ground path for CR2, turning on the fault indica-
tor.
MAINTENANCE
TEST PROCEDURE
The RXFE module has to be tested for Noise Figure,
Gain, Third Order Intercept Point, Isolation etc.. With proper
current drawing of devices, Bandwidth and Conversion Gain
the RXFE module will meet its specifications. The following
are test procedures will verify proper Conversion Gain and
current drain:
1.
Supply 12 Vdc to pin 15A, B, C. (1C is ground.)
2.
Inject the desired RF signal into RF IN at a level of
-10 dBm.
3.
Inject the desired local oscillator signal into LO IN
at a level of 0 dBm [LO frequency = RF frequency -
21.4 MHz (G3, G4) + 21.4 MHz (G7)].
4.
Measure the IF OUT power at 21.4 MHz, the ratio of
RF IN to IF OUT is -2 dB
±
1 dB.
5.
Measure the current drawn by the RXFE module.
Typical current drain is 290 mA.
ALIGNMENT PROCEDURE
Alignment for the Receiver Front End module consists
of tuning the five-pole Preselector Filter only. Normally, the
RXFE should only need the fine-tuning procedures. For a
major receiver frequency change, the RXFE needs to be
adjusted using the major-retuning procedures.
For Fine-Tuning
1.
Supply 12 Vdc to pin 15A, B, C. (1C is ground.)
2.
Inject the desired RF signal into RF IN (J2) at a level
of -10 dBm.
3.
Inject the desired local oscillator signal into LO IN
(J3) at a level of 0 dBm [LO frequency = RF fre-
quency - 21.4 MHz (G3, G4) + 21.4 MHz (G7)].
4.
Detect IF signal at 21.4 MHz. Slightly adjust L1 to
L5 to get maximum power (don’t adjust more than
ten degrees). If an RF Voltmeter is used, connect a
Low Pass Filter (LPF)to the IF OUT (J4) to attenuate
high frequency components. The corner of the LPF
should be set for 40 MHz.
5.
Repeat Test Procedure steps to verify conversion
gain and current drain.
For Major Retuning
The best way to do a major retuning of the RXFE is with
swept frequency tuning. The swept frequency tuning can be
done using a Spectrum Analyzer and Tracking Generator.
With proper Injection power and current drain, the frequency
response of the Preselector Filter can be seen by viewing the
RF to IF port feedthrough on the spectrum analyzer. This
feedthrough is typically 35 dB down from the input level at
the RF port. Use the following procedure for swept fre-
quency tuning:
1.
Supply 12 Vdc to pin 15A, B, C. (1C is ground.)
2.
Inject the Tracking generator output at 0 dBm into
the RF IN connector, (J2).
3.
Inject local oscillator power at 0 dBm into the LO IN
connector, (J3) [LO frequency = RF frequency - 21.4
MHz (G3, G4) + 21.4 MHz (G7)].
4.
Preset the height of slugs with respect to the top of
five-pole cavity as follows (Table 2):
Table 2
5.
Center the spectrum analyzer at the desired frequency
and set the reference at about -30 dBm. Adjust L1 to
L5 for best possible response.
HEIGHT (in inches)
Frequency
(MHz)
L1
L2
L3
L4
L5
450
15/64
16/64
17/64
17/64
16/64
454
16/64
17/64
17/64
18/64
15/64
458
16/64
19/64
19/64
19/64
17/64
462
18/64
19/64
20/64
20/64
18/64
466
21/64
22/64
23/64
21/64
20/64
470
22/64
24/64
24/64
23/64
22/64
SYMPTOM
AREAS TO CHECK
READING (TYP.)
LOW CONVERSION GAIN
Check Vcc
12 V
Preselector Loss
3.5 dB
Preamplifier Gain
11 dB
Image Rej. Filter Loss
2 dB
1st Mixer Conversion Loss
6.5 dB
1 L.O. Level (@ mixer L.O.
+22
±
2 dBm (G3, G4)
port)
+14
±
2 dBm (G7)
LED INDICATOR ON
Check Vc of Q1
10 V
Check Vc of Q3 and Q8
10 V
IF FREQUENCY OFF
Check L.O. FREQUENCY
L.O. frequency = RF frequency - 21.4 MHz (G3,G4)
+ 21.4 MHz (G7)
LOW L.O. POWER*
Injection Amplifier Gain
23
±
2 dB (G3, G4)
18
±
2 dB (G7)
Injection Filter Loss
2 dB
*
NOTE: For troubleshooting the gain or loss, the RXFE needs to be under the normal operating condition:
•
12 Vdc supply.
•
Inject L.O. power at a level of 0 dBm into LO IN (J3), [LO freq. = RF freq. - 21.4 MHz (G3, G4)
+ 21.4 MHz (G7).
•
Inject the desired RF signal at a level of -10 dBm into RF IN (J2).
•
Terminate the IF OUT (J4) with a good 50 ohm impedance.
•
Use a Spectrum Analyzer and 50 ohm probe (with good RF grounding) to probe at the input and output of
each stage to check its gain or loss (see schematic diagram).
TROUBLESHOOTING GUIDE
LBI-38673F
2
Summary of Contents for 19D902783G1
Page 6: ...SCHEMATIC DIAGRAM RECEIVER IF MODULE 19D902494G1 19D902504 Sh 1 Rev 6 LBI 38643C 5...
Page 7: ...SCHEMATIC DIAGRAM RECEIVER IF MODULE 19D902494G1 19D902504 Sh 2 Rev 6 LBI 38643C 6...
Page 42: ...RECEIVER FRONT END BOARD 19D902490G4 G7 OUTLINE DIAGRAM 19D902490 Sh 4 Rev 6A LBI 38673F 5...
Page 43: ...ASSEMBLY DIAGRAM RECEIVER FRONT END MODULE 19D902782G3 19D902782 Sh 1 Rev 6 LBI 38673F 6...
Page 44: ...ASSEMBLY DIAGRAM RECEIVER FRONT END MODULE 19D902782G4 G7 19D902782 Sh 2 Rev 6 LBI 38673F 7...
Page 45: ...SCHEMATIC DIAGRAM RECEIVER FRONT END MODULE 19D902782G4 G7 19D904768 Sh 1 Rev 6 LBI 38673F 8...
Page 47: ...SCHEMATIC DIAGRAM RECEIVER FRONT END MODULE 19D902782G3 19D903498 Rev 7 LBI 38673F 10...
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Page 56: ...ASSEMBLY DIAGRAMS LOW PASS FILTER MODULE 19D902856G3 19D902856 Sh 1 Rev 0 LBI 38674F 7...
Page 71: ...ACCESSORIES ANTENNA SWITCH 19B235897P2 LBI 38675E 9...
Page 80: ...SCHEMATIC DIAGRAM RECEIVER IF MODULE 19D902494G7 G11 193D1065 Sh 1 Rev 3 LBI 39123E 7...
Page 81: ...SCHEMATIC DIAGRAM RECEIVER IF MODULE 19D902494G7 G11 193D1065 Sh 2 Rev 3 LBI 39123E 8...
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