Heathkit SG-8 Manual page 21

Should the oscillator trimmer of the short-wave band have a wide tuning range. it may be pos
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sible to pick up and "peak" a signal with two different settings of the trimmer. Should this the
the case, use the settino with the least canacrity to insure that the agrillator is tuned ahnve tha
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incoming signal.
FM RECEIVER ALIGNMENT
It is the standard practiceto alignthe IF amplifier of an FM receiver (tuner) before aligning the
ep
' RF and oscillator sections ju s in AM receivers. However, the exact technique of alignment
depends on whether a limiter discriminator or a ratio detector is used. Where a limiter and
discriminator are used, usual practice is to align the IF section up to the input of the limiter
first. Then align the. discriminator as a separate step. When aligning the IF, RF and oscilla-
tor sections, the grid current of the limiter may be used as an output indicator. Although the
voltage across a limiter grid resistor, measured with a VTVM, willserve in many cases, it is
not an ideal indication. A typical limiter and discriminator stage is shown in Figure 14. Pro-
per alignment technique for the complete FM receiver is as follows:
LIMITER
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Figure 14
(1) Connect an output indicator by (1) attaching a vive across the limiter grid resistor, or
(2) breaking the circuit at the grid of the limiter and insertinga microammeter r wi
imum range of around 150 microamps. if this method is used, be sure and bypa SS
with a .05 pid condenser to ground. See point X in Figure 14.
(2) Connect a signal generator tc the input of the mixer stage and turn on both the signal gen-
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ceiver and the generator to reach their normal operating temperature. In the case of FM
ia is usually 1 15 to 20 minutes before c complete stabilization can be obtain
signal generator to the IF value of the set. This is usually 10.7 mc. The un-
modulated RF output of the signal generator is used
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Peak all IF trimmers for maximum meter readings. If the IF is considerably out of align-
a
w
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ment so that very little meter reading is obtained, it may be necessary to connect the sig-
nal generator to the last IF stage and align this portion of the circuit first. Then work back
toward the mixer stage, rechecking previous IF adjustments at each point.
(4) Connect a VITVM between point 1 and ground as shown in Figure 14. Adjust the trimmer or
slug "J" for maximum reading using a low VTVM range.
(5) Transfer the VTVM connection to point 2 and adjust trimmer "H" for a minimumvoltmeter
reading.
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