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Although there are many variations of this amplifier, this is the most basic, and popular example. All transmitter power stages use this type of amplifier. Single ended, with a very short on time for the active device, just enough to excite the tank circuit enough, so that it starts oscillating. Typically these types of amps are very efficient and are only used in RF applications, because the output distortion is very gross over a wide range of frequencies, but can be filtered for a specific frequency. The input is always filtered with a low pass filter, to prevent the amplifier from leaking RF noise back to the power supply. This specific example is slightly biased. The transistor is still non conducting in idle condition, but the base voltage has been brought a little closer to the activation point of 0.7V to decrease the input voltage requirement. See you always waste 0.7V of input with these amplifiers. You need at least 0.7V to enable the transistor, but bringing the bias point a little closer to the activation point makes it easier to enable the transistor ( you'd need let's say 200mV to enable it). You can take it directly to class A mode if you wish, but then you lose a lot of efficiency for some linearity which is infeasible, since I've added a several order low pass filter at the output to clear out any harmonics. Some of the specs are:
- Drawn Power - 3.3W
- Output Power - 2.3W
- Efficiency - 68%
- Rqnge of transmitter - depends, can be as far as 10km in the right conditions, but since the conditions are many, I'd say more like 2-5km
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