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The 1.5v bias voltage of the filter section is provided by the output voltage of the phasing strip which in
turn gets it bias voltage from the output of the AF preamp. The AF preamp gets it bias voltage in turn
from the detector itself.
In case someone is wondering what happened to the ninth pole in the NC2030 filter, the frequency roll
off of the detector is used as the ninth poll.
R/C Audio Filter – High pass
Figure 133. 400 Hz High pass filter schematic
The low frequency roll off of the receiver is far less critical than the high frequency roll off. Thus, only
three poles of selectivity were used in this filter. This filter has no audio gain. The 18K resistor, which
is part of the filter, is also used to provide a 1.5v bias voltage to the stage.
Norcal NC2030 v5
12-18-05
Page 115 of 128
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