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QAM modulation is vital to most of modern digital RF radios out there. But what exactly the modulator does? We explain in this episode of Inside Wireless! Learn more: rfelements.com/
Modulation is a process of encoding the digital data - 1 and 0s - onto an RF wave that is more suitable for wireless transmission. The QAM modulator is the circuit inside the radio that takes care of this.
If not sure about the basics of QAM modulation, check our previous video: • Inside Wireless: QAM m...
The basic idea is that the incoming data stream is divided into two branches. The length of the 'symbol', or, the amount of 1s and 0s processed in parallel determines the depth of the modulation. The higher the number, the more data we transfer during one transmission.
The RF carrier signal is brought to both of these branches and multiplied by the amplitude (strength) determined by the input data stream. One branch is called I (in-phase) and the other Q (quadrature). The quadrature means that the I and Q waves are shifted by 90 degrees with respect to each other. After that, the I and Q signals are added to produce the output RF signal.
The increasing data density with growing length of the input symbol is easily seen on an IQ diagram showing each unique symbol the modulator can produce. The higher the data density in the same space, the higher the SNR of the signal needed for successful data transfer - check out this video for detailed explanation: • Inside Wireless: Noise...
Spectral efficiency is a measure of increasing data transfer efficiency with growing QAM depth.
The distances at which the typical WISP radio is capable of working at highest MCS rates are very short - this is again connected to the SNR requirement of the signal and the output amplifier linearity - check our video on this topic: • Inside Wireless: MCS i...
00:00 - Intro
00:42 - QPSK / 4 QAM
01:41 - Constellation diagram
02:26 - 16 QAM - 1024 QAM
03:35 - Spectral Efficiency
04:46 - RF noise challenge
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