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and it provides the IF video output and the X and Y recorder outputs.
Video Filter @
The Video Filter is an RC low pass filter with selectable R and C. The series resistance R
is one of two values controlled by switch U7. When the switch is closed (0), R17 is short
circuited and the series resistance is minimum. In this state, video bandwidths from 3 kHz to
3 MHz are attainable (The 3 MHz nominal bandwidth is attained when Q14 through Q20 are
turned off). When switch U7 is open (l), the series resistance R is high, approximately equal
to R17 and video bandwidths from 1 Hz to 1 kHz are attainable. Shunt capacitors C5 through
transistors can be on at any one time. Each capacitor except Cl1 is used with the high series
resistance for the lower bandwidths and the low series resistance for the higher bandwidths.
Log Expand @
The Log Expand circuit allows four different amplitude scales: 10,5,2, 1 dB/DIV. Changes
in the amplitude scale are accomplished by first amplifying the video signal, then attenuating
it various amounts. This is accomplished by FET input amplifier U2, which offsets the input
-5 V and whose gain (set by R22 and R21) is 5. The offset is set by the current through Ql.
This current source is adjustable using OS potentiometer R14. Switching transistors Q4, Q5,
and Q6 are turned on or off to achieve voltage divider ratios of l/10, l/5, l/2, and 1. Diodes
CR2 and CR3 clamp this attenuated signal at about -1.2 V to prevent forward biasing
any switch in the off state. A final amplifier consisting of Q7, QS, and Q9 amplifies this
attenuated signal by 4 and offsets the output +2 V. A +2 V output corresponds to a full-scale
signal. This final amplifier is a two-stage amplifier. The first stage is a FET input stage made
up of dual FET Q7. The first-stage output is multiplied by the transistor inverter QS, whose
output is buffered by an emitter follower Q9. This output is fed back to the inverting input
through a resistor divider stick. Gain of the amplifier is adjusted by ZERO potentiometer
R32, and offset for full scale is adjusted by FS potentiometer R36. Diode CR1 clamps the
output at about -1.2 V.
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