TM 11-6625-586-45
Figure 5-5. Internal modulation, test setup.
Frequency (MHz)
Table 5-6. Bias Adjustment Guide
22
A
Always perform deviation and distortion readings at
1.
32
B
low, med and high points in a band, even if incorrect,
46
C
before changing the bias.
70
D
2. To adjust bias, begin by raising in 0.3-volt increments
(0.5 volt increments for band D) and continue as long
At each frequency the total harmonic distortion
as there is improvement in the results. When results
should be less than 8 percent (22 db below refer-
deteriorate by raising the bias, lower the bias or try a
ence).
setting between two previous bias levels.
e. Connect HI-RF terminal of unit. under test
3. Following a bias readjustment, always reset the true
deviation to its optimum value, according to table 5-5.
4. Always set the bias with frequency at mid-band.
AC terminal of multimeter.
5. Hints for band B:
f. Set RF OUTPUT switch to 62.5 KUV.
(a) high distortion at low end - increase bias by 0.4
g. Repeat step d, above.
volt with R28.
(b) deviation readings are low, distortion good - de-
5-14. Alignment of IF Assembly for
crease bias by 0.3 volt.
Operation in the 1.3 to 4.2 MHz
6. Hints for band A:
Range
(a) high distortion at high end - increase bias by 0.3
volt
a. The IF assembly is capable of operating at
7. Specifications:
any frequency in the range from 1.3 to 15.0 MHz.
(a) Deviation (all bands)
In order to operate the oscillator from 1.3 to 4.2
40 3.5 kHz
MHz, the procedure below should be followed:
30 3 kHz
b. Materials Required:
20 2 kHz
(1) Supply of 1/4 watt, 5% carbon compo-
10 1 kHz
sition resistors from 47 to 1000 ohms. Suggested
(b) Distortion*
band A
4% maximum
values 47, 68, 100, 180, 220, 270, 330, 390, 430,
band B
3% maximum
470, 560, 680, 750, 820, 910, 1000 ohms.
band C
2.5% maximum
(2) In addition to the capacitor value found
band D
2% maximum
from the graph (fig. 56) for the frequency of
interest, three values 10, 20 and 30% higher and
*170 greater distortion permitted at 40 kHz
three values 10, 20 and 30% lower. (Dipped mica
or ceramic, 10%.)
5-13. Spurious RF Outputs
(3) One capacitor 0.01 uf (10%).
a. Connect LO-RF terminal of unit under test
c. Test Setup
(1) Remove IF amplifier assembly from sig-
terminal of multimeter.
nal generator.
b. Set OPERATE-OFF-STANDBY switch to
(2) Remove sinews holding the circuit board
OPERATE, FUNCTION switch to MOD OFF,
A2A1 and pull this unit out of the IF assembly.
RF OUTPUT switch to 0-10 KUV and LO RF
NOTE
UV control to 10 KUV.
c. Adjust LO-HI RF SET TO LINE control
Do not unsolder any wires.
for 1.0 indication on IF UV RF SET TO LINE
(3) Set the printed circuit board on a bench
mater.
taking care to avoid a short circuit. between the
IF assembly and the printed circuit board when
following RF frequencies:
the units are energized.
5-12 Change 1
