All circuitry, with the exception of the stereo LED indicator, is
accommodated on the printed circuit board (coded AM_ST), and fitted within
1.675 by 1.5 inch layout. Parts layout and the six required connections on
this printed circuit board are shown on the second page of these instructions.
Installation
For quiet, clean, stereo reception, the I.F input signal to the decoder input
must be between 90 milli-volts and 120 milli-volts peak-to-peak. If the host
tuner has a higher I.F output, a resistor voltage divider must be added to
drop the I.F to the required level for the AM stereo decoder board.
I.F input is derived from the mixer output or I.F stage preceding the
detector diode or detection circuitry inside the host receiver or tuner. AGC
voltages are generally obtained from the detector, so the existing detector
circuit should be retained. To avoid conflict with the two audio channels
coming from the stereo decoder, the tuner’s existing mono audio outputs first
must be disconnected (usually at or near the band-switch).
Decoder board may be mounted in any convenient place inside your host
tuner, however keep it away from all metal and heat sources, such as power
transformer, output transistors, heat sinks, et cetera. Use very short
shielded cable for the I.F input and audio connections, and connect the cable
shields to tuner’s ground point at one end only. Common ground connection to
the decoder and the tuner is via the tuner’s power supply. Failure to observe
this precaution could result in ground loops. Ensure that the power is applied
only to the decoder when the host tuner is selected to “AM” band and tuned to
receive AM stations.
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