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(from -15.9 dB to +50 dB); it d evelops a nominal +lO V bias supply; and it provides the
18.4 MHz LO frequency to A4A6Al Up Converter and A4A6A2 Down Converter.
Step Gain 10 dB + Calibration @
This circuit is configured as a non-inverting operational amplifier. It provides a minimum of
about 2 dB gain (adjustable by CAL potentiometer R33) and a maximum of about 12 dB
(adjustable by 10 dB potentiometer R32). (See 1 F'gure 1.) The PIN diode CR5 functions as a
variable resistor that has about 1 K resistance at minimum and 700 of resistance at maximum
gain. When the SGlO line is not sinking current (SGlO is off), the PIN resistance is controlled
by R32. If the CAL potentiometer is adjusted, R32 must be adjusted also.
Figure 1. Step Gain 10 dB + Calibration, Equivalent Circuit
Step Gain 20 dB-1 @I
Step Gain 20 dB-2 @
This circuit is similar to the Step Gain 10 dB + Calibration circuit, except that the gain
range is from 0 dB to 20 dB. PIN diode CR6 functions as both a switch and as a variable
resistor. When the SG20-1 line is low, CR6 is turned on by current adjustable by 20 dB-1
potentiometer R44. More current through the PIN causes the PIN to have a lower resistance
and the amplifier to have more gain. The Step Gain 20 dB-2 circuit is identical in operation
to the Step Gain 20 dB-1 circuit.
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R E S I S T A N C E
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