Learning Event 3: The PFN

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Learning Event 3:

THE PFN

1. Figure 54 shows that the PFN is an ATL. Recall from a previous lesson,

Artificial Transmission Lines, that one of the major uses of ATL is to form

radar pulses.

You learned that the ATL determines the pulse width and

shape. At this time, you should review the previous lesson concerning basic

principles of ATL.

Note carefully those sections dealing with the

following:

a. The charge of an ATL through a source resistance (Rch) greater than

the characteristic resistance (Rc) of the ATL.

b. The discharge of an ATL through a load resistance (RL) equal to the

characteristic resistance of the ATL.

2. Now look at Figure 54 again. Part A shows a simplified schematic of the

charging circuit of the modulator.

The high-voltage power supply charges

the PFN to 6,000 volts DC through the charging impedance. In this case, the

charging impedance is a resistor, called the charging resistance Rch. The

characteristic resistance (Rc) of the line is less than the source and

charging resistances.

Therefore, the PFN charges exponentially to the

source voltage of 6,000 volts DC. No pulse is formed across the load during

the charge cycle because the impedance of the load (magnetron and its pulse

transformer) is very low and the charge time is very long.

Figure 54.

Charge and Discharge of the PFN.