Heathkit AR-14 - Page 81

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LEFT WAVEFORM
LEFT WAVEFORM
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RIGHT WAVEFORM
38 KC
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SWITCHED
DETECTION
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LEFT WAVEFORM
0
RIGHT WAVEFORM
0
RIGHT WAVEFORM
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012 CONDUCTS
ONLY
ON THESE
38 KC PEAKS
T7
012
LEFT WAVEFORM
LEFT WAVEFORM
FROM 010
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38 KC
1 111 1
0
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RIGHTI WAVEFORM
011
RIGHT WAVEFORM
011 CONDUCTS
ONLY
ON THESE
38 KC PEAKS
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LEFT WAVEFORM
FROM 09
Figure 15
The left and right channel audio signals then are
applied to individual 38 kc PEC filters that
remove any remaining 38 kc signal. Proper
de-emphasis of each signal is provided by the
combinations of the PEC components and ca-
pacitors C57 and C58. The stereo signals are
then connected to the Left and Right channel
outputs.
When the Phase switch is in the "out" position,
a 38 kc bandpass filter is connected into the
circuit (coil LS and capacitor C52. This circuit
allows only the 38 kc subcarrier channel to pass
through to transistors Qll and Q12. The phase
control is used to adjust for proper phasing
between the reinserted 38 kc carrier and the
38 kc subcarrier signal. This ins'ures maxi-
mum separation from the receiver. (The Phase
control is adjusted by listening for maximum
sound in the subcarrier signal; the presence
of main channel sound would make this adjust-
ment impossible.)
A small amount of the 19 kc signal is coupled
from coil L7, through capacitor C38, to the base
of stereo indicator amplifier transistor Ql 3.
This 19 kc signal is only present when a stereo
signal is being broadcast.