AD9361 transmitter testbench

I am simulating Analog Devices RF AD9361 transmitter toolbox module. The design shown in Modelling and Simulating Analog Devices’ RF Transceivers with MATLAB and RF Blockset (@ 23:26 minute) has Peak value at 2.14 GHz for the same reference model provided from Mathworks I am geeting peak at 0 Hz. (i.e the transmission is still happening at baseband and not at passband frequency). How can I get this same spectrum at 2.4GHz RF frequency (i.e How can I set centre frequency to 2.4GHz)?

Can somebody help me in solving this problem?

Here I have also attached the photo of my result for your reference

Answer 1

[Abhishek]

Hi @焓希,

I understand you want to configure the AD9361 transmitter model in MATLAB to shift the output signal from baseband to a center frequency of 2.4 GHz.

To achieve this, you can follow the steps (reproduced in MATLAB R2024b):

• Open the updated AD9361 transmitter model (which has the option to specify Local Oscillator (LO) frequency directly) by executing the below command in MATLAB:

    open ad9361_tx 

• Uncomment the “LO Signal” and “Spectrum TX” block.
• Double click on the “ad9361_TX” block to set the desired LO Frequency (Hz).

However, even after setting the LO frequency, the “Spectrum Analyzer” will still display the signal centered at 0 Hz. This is because the “Offset (Hz)” parameter is set to 0 by default, so the spectrum is plotted relative to baseband. The Spectrum Analyzer displays signals within the Nyquist interval, which spans from for two-sided spectrum. As a result, the center frequency appears at 0 Hz unless otherwise specified.

To shift the spectrum to show the actual transmit frequency:

• Go to the Scope tab of Spectrum Analyzer.
• Set the Offset (Hz) parameter to LO frequency.

This effectively shifts the spectrum to be centered around the specified RF frequency instead of baseband as shown in the figure below.

For more details, please refer to the "Spectrum Analyzer" documentation, which explains how frequency offset affects the displayed spectrum:

https://www.mathworks.com/help/releases/r2024b/dsp/ref/spectrumanalyzerblock.html#btqjkji_sep_mw_e13926e1-f94e-477a-837f-bc000fe3b4b0_head