CRAIG KENDRICK SELLEN
ADAMS HIGHRISE
SCRANTON PA, USA

Did you ever wonder how they put the revolving sweep going around in a circle on a cathode ray tube (CRT) on a radar screen? They use a revolving yoke mounted on the neck of the tube. But this device uses a different type of scanning operation. It uses circular sweep going around in a circle on the outer edge of the CRT tube. And another, sweep action going outwards from the center of the cathode ray tube on the display chassis and drops back to the center again when the electron beam is cut off, and the deflection yoke magnetic field collapses. The spot is returned to the center for a microsecond, and then the yoke starts its deflection outward to the edge again. This action starts over again and again. This gives a vector scan that appears to be a scanning line sweeping around just like a real radar PPI indicator.
The circuit consists of a two phase oscillator that is in low, low frequency that puts out a signal which are 90* apart. Which in other words that are sine-cosine signals that is 90* apart. Theses two signals are generated by the tube op-amps. This makes the electron beam sweep around in a circle at the very edge of the CRT. This sweep is blanked ordinary. The second sweep is from the center of the display tube to the outer most edges of the tube this is done when the two triodes V7a and V8b conducts at the same time giving a vector voltage to the edge of the tube and then drops back to the center when the triodes V7a and V8b stops conducting giving a line on the tube. When the two triodes conducts again the sweep line is swept out from the center to the outer most edges of the tube and drops back center again when the two triodes which acts as clamps starts conducting. This process repeats again and again and goes back and forth which gives a sweeping line going around in a circle approx, one sweep around in 4 seconds, which looks like a real radar display. 
The pulse generator which consists of a 6J6A tube is another oscillator giving a clamping voltage to the two triodes acting as control clamps, which turns them both on and off at a rate of about 450Hz.
The PPI circuits runs on a well filtered DC power supply at about 250V single ended for some of the circuits, while the sine-cosine op-amp section requiring +-250 to 300V DC. 
The switch S1 is used to adjust the controls on the display CRT chassis and is used to center the circle on the CRT and places it in the center of the screen, and is used only in setup and test. And then after that is left alone. 
Discription of the schematics
first schematic, is the high voltage for the CRT and Horizontal and Vertical outputs to drive the CRT yoke.
second schematic, is the timebase and pulse circuits
third schematic is the clamps and switching circuits
fourth schematic is the single ended power supply to drive the H.V. section for the anode 10kVa, and the other circuits.
fifth schematic is the CRT grids and video amp. circuits
sixth schematic is the split power supply for the sine-cosine generator.
seventh schematic is the sine-cosine generator

View or Download Documents