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Considering the power amplifier for complex modulate signal

caoquyen164

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Dear all,
I'm choosing a 1W power amplifier for QAM 256, 20MHz bandwidth signal.
as far I know, the QAM256. 20MHz signal is such like the below.
signal.PNG

the the total power of 20mhz signal is 1W=30dbm, the power of a 1HZ bandwidth signal is 30-10log(20*10^6)= -43dbm. besides, the PAR of 256QAM ~ 7-> the peak power of a signal is -36dbm.
so, I just need a power amplifier which can stand only -36dbm (may be need some more back-off). Did I wrong ?
 

Marcinstein

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Hi,
Peak power of a signal isn't -36 dBm. Its rather -36dBm/Hz which is power spectral density. First you must define peak power of your signal to properly fit amplifier.
Marcin
 

Coores

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Are there any guidelines on how to define the peak power of the signal properly?
 

FvM

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Crest factor of different QAM signals can be easily found in literature, just ask Google. It's 4.23 dB for 256QAM, means you need at least 2.7 W amplifier peak power for 1 W average. I presume it's a single carrier signal.
 

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