|
I've mapped the key highlights of the circuit. As you can see the first stage is a normal common collector amplifier. Nothing unusual, except that the stage is not biased. The transistor rapidly turns on at about 700mV. The input constantly varies between +800mV and -800mV, meaning that the transistor will almost always be at rest, conducting for only 10-20% of the whole cycle. This extends the efficiency to 80%. Now the output of the first stage (blue) , as you can clearly see, is very distorted, just a mere remnant of the original wave. This is why it's not suitable for AF, and this is why it's suitable for RF...You can easily say that the output only contains the original frequency and nothing of the shape. If we were to directly transmitt the output of the first stage, a lot of harmonic EMI will be generated, clouding surrounding stations of an even number. So if you're transmitting on 100Mhz then you'll be inadvertently transmitting also at 200Mhz,300Mhz,400Mhz... The good thing is, though, you can use an output filter to restore the original wave (yellow), into a clean, harmonicless output, suitable for an interference free transmission. The more output filters, cleaner the signal is a rule of thumb
|
