Fig. 5. Transistor "booster"rf power ampJifier circuit. Component values for di/ferent frequencies and voitages are discussed in the text and tabulated in Tables I, U and III.

Assume for the moment that capacitor CI is shorted out and that capacitor C3 in series with coil LI has a capacitance of 25 pF, equivalent to a capacitive reactance of 44Q at 145 MHz. Ignoring stray circuit inductances, the inductance of the coil will have to be increased from .011 /iH to .055 juH to overcome the effects of the capacitor. Thus, adding capacitor C3 to the circuit permits making coil LI a practical size. Capacitor C4 performs a similar function in conjunction with coil L2 in the output network.

Within limits, the series capacitors permit cancelling out any desired percentage of the

TABLE II!

coil and circuit inductance. To be effective, they must have tow minimum capacitances and very low self inductance. Such series capacitors are seldom required on frequencies below 50 MHz. On the other hand, the calculated capacitance values in low-imped ance I networks become rather large at frequencies below 14 MHz,

At 7.2 MHz, for example, the input capacitor of i\n L network designed to match 50ii to a 2.5load would have a capacitance of over 2000 pF. But if the 50fi can be made to appear as a higher resistance to the L network, the input capacitance (C2) can be decreased.

Was this article helpful?

## Post a comment