HP (Hewlett-Packard) HP 85660B ユーザーズマニュアル

becomes a voltage follower maintaining the voltage at the cathode of CR5 at the same voltage
as on U7 pin 12. In this situation, R32 and R31 are effectively in parallel with the current
sense resistor of the coil driver circuit. R31 is used to adjust the magnitude of compensation,
while 

 is used to adjust the frequency at which the compensation occurs. In a similar

manner, 

 B, C are used to correct for higher frequency nonlinearity.

The PIN switch driver converts the TTL logic level LO-BAND signal to the $20 

 V

signal required by the Second Converter. The TTL level at 

 to 34 is input to the base of

 A high at the base of Q21 turns Q21 on, turning on Q4, which pulls the collector of Q4

approximately 

 V. This turns on Q3, providing the 

 V signal to the PIN drive output,

 to 35. A low input on the LO-BAND TTL input turns Q21 off, which turns Q4 off. The

collector of Q4 then goes low, turning on 

 and pulling the PIN drive line to -10 V.

The PIN drive signal is also used to turn the 3.3 

 oscillator on in A-Band, and off in other

bands. When the PIN drive goes high, 

 is turned on which pulls its collector to -10 V. The

-10 V is the negative bias for the 3.3 

 oscillator. When the PIN drive goes low, 

 is

turned off, dropping the oscillator bias current to zero, which turns off the 3.3 

 oscillator.

In the on state, resistor 

 is used to adjust the oscillator bias current to 15 milliamps.

The coaxial RF switch is driven by darlington amplifiers 

 and 

 A high input on the

LO-BAND line drives the outputs of 

 low, and 

 high. A low output at 

 drives the

Coaxial RF switch relay to the A-Band (0 to 2.5 

 position. The reverse occurs with a

low input which drives 

 output low, which forces the coaxial RF switch relay to the B-E

Band (2 to 22 

 position.

To correct for different input mixer conversion efficiencies and gains in the individual

frequency bands, the IF gain is changed. This is done in the 

 Last Converter by varying

the current through PIN attenuator diodes in the 21.4 MHz amplifier. This current is
controlled by Q12, Q14 to Q17, and 

 In A-Band, the high output on the PIN drive line

breaks down zener 

 and turns on 

 This applies -40 V to the potentiometer R21.

Adjusting R21 varies the current in the step gain in A-Band.

The gain of 

 Last Converter is adjusted in each band as each transistor, 

 Q14 to

Q17, and 

 is turned on for each individual band.

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