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Purpose of Power Amplifier

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SDRookie

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Study PA recently. Have lots of questions. If I already have an op-amp and I need to sent a signal to antenna, why don't I just add a source follower at the output? Why do I need to build an additional block?
 

An opamp works at fairly low frequencies, like audio that averages 1kHz. A radio transmitter works at fairly high frequencies. AM radio stations are at around 1MHz that is about 1000 times higher than audio.
FM radio stations are at 100MHz that is 100,000 times higher than audio. Audio signals modulate the high frequency carrier oscillator that might feed an RF power amplifier that feed the transmitting antenna.
 
A source follower is a buffer. It can provide current gain
but not voltage gain (always less than 1.00000000...).
It -could- be used to boost "op amp" output current.
But for RF you would not likely be able to use an op amp,
for frequency reasons especially but also because it's
likely to have very poor gain @ frequency and higher
than desirable noise.

Why, or whether you need a designed PA, depends on
the goals for the assembly. If you can do it as described,
in fact, then have at it. But expect to find reasons why
you need to do better, as you proceed with your first
stab at lineup design and analysis.
 
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