[SOLVED] Constellation Diagram Using RF Test Equipment - Adalm Pluto

[RookieTadehEERF]

Hey fellas,

I'm new to signal processing/digital communication. I have a little bit of a background in RF and analog, but very little digital knowledge. I am currently exploring with Adalm Pluto.

My question is about the constellation diagram. I understand, (please correct me if this is wrong), that in the constellation diagram, the vertical axis plots the amplitude and the horizontal axis plots the phase of a modulated waveform. The closer these modulated waveform "dots" or data points are to the original transmitted signal, the more the clarity of data received.

With that being said, I am used to using test equipment to verify all of my theory predicted results in real life. How do you approach this in digital comm world?

Another issue that has lead me to the question above is when I transmit a simple sine wave, and then hop on a different frequency, the time that it takes for this transition is around 100ms; however, when I try and use QPSK modulation and hop, this transition takes around 5 times longer. I understand that the processing power of the AD9363 that is used in Adalm Pluto might be a little slow, but 700MHz to 1300MHz ought to be enough, or so I think, for a better result. Any ideas why this time delay might occur? I believe there is very little time delay in the world of RF/analog, so I'm sure it is coming from the digital side of things.

Also, I was wondering, how do you determine the bandwidth of a modulated signal? For example, when I modulate a signal using QPSK sending data packets, how do I know how much bandwidth I need in my receiver to ensure I can receive the entire signal.

Thanks in advance!

T

 

[kaz1]

Hey fellas,

I'm new to signal processing/digital communication. I have a little bit of a background in RF and analog, but very little digital knowledge. I am currently exploring with Adalm Pluto.

My question is about the constellation diagram. I understand, (please correct me if this is wrong), that in the constellation diagram, the vertical axis plots the amplitude and the horizontal axis plots the phase of a modulated waveform. The closer these modulated waveform "dots" or data points are to the original transmitted signal, the more the clarity of data received.

With that being said, I am used to using test equipment to verify all of my theory predicted results in real life. How do you approach this in digital comm world?

Another issue that has lead me to the question above is when I transmit a simple sine wave, and then hop on a different frequency, the time that it takes for this transition is around 100ms; however, when I try and use QPSK modulation and hop, this transition takes around 5 times longer. I understand that the processing power of the AD9363 that is used in Adalm Pluto might be a little slow, but 700MHz to 1300MHz ought to be enough, or so I think, for a better result. Any ideas why this time delay might occur? I believe there is very little time delay in the world of RF/analog, so I'm sure it is coming from the digital side of things.

Also, I was wondering, how do you determine the bandwidth of a modulated signal? For example, when I modulate a signal using QPSK sending data packets, how do I know how much bandwidth I need in my receiver to ensure I can receive the entire signal.

Thanks in advance!

T

constellation diagram are I value versus Q value. The closer they are to ideal points the better (the EVM).

In the case of FDM systems (QPSK, QAM) The baseband width is decided by Rs/2 i.e. half symbol rate. In the air it becomes Rs. The data rate is Rs * 2 for QPSK as every symbol codes two bit patterns

As to frequency hopping it is your setup too angry. speeds like 1300Mhz are not known in digital chips except may be RF chips.