1M ～ 50MHz, 1W wide-band power amplifier. Figure 28-1 is the use of 2SC1970, frequency 1 ～ 50MHz, output 1W wide-band power amplifier; input and output uses a wide-band transformer composed of ring coils for impedance conversion, The ring-shaped magnetic core is the FT type of ceramic ferromagnetic core. 2SC1970 is a power transistor for the 170MHz frequency band, so it can be used in a wide band amplifier in the VHF band. In addition, due to the high power gain, special treatment is required to avoid oscillation. In the circuit diagram, the coupling capacitor (CoupIing
Both Capacitor and Bypass Capacitor are made up of 2 to 3 0.01μF ceramic capacitors connected in parallel. The most important thing is to reduce the impedance. At the same time, the path of current circulation is also wider. In addition, the bias diode 1S1558 needs to be thermally coupled with the 2SC1970. The place to be adjusted is the quiescent current (Idling Current). The variable resistor for base bias adjustment with 500Ω is set at about 30mA. Figure 28-2 is the frequency characteristics of the circuit. The input is set at 20mW. The output power when the frequency is changed is maintained at about 1W from 1M to 50MHz. The sudden increase of the output near 30MHz is due to resonance caused by stray capacitance. .
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