Why does my USRP X310 receive signals incorrectly

Hi！

I am using the USRP X310 to transmit and receive FMCW signals to achieve radar ranging. I transmit an upfrequency signal with a frequency ranging from 5GHz to 5.2GHz. However, in the received signal, there is always a downfrequency signal of about 0 to 15 microseconds, as shown in Channel 2 in the picture (Channel 1 is an ideal transmitted signal), which is very abnormal. Moreover, at the end of the received signal, there is always an error situation where the signal amplitude is 0. The attachment is the code I modified Based on the sample code "FMCW Radar Waveform Based Range Calculation Using Time Trigger", but the situation where the sample code cannot be accurately received cannot be achieved. May I ask how I should solve this problem? Thank you very much!

我在使用USRP X310进行发射和接收FMCW信号，以实现雷达测距。我发射的是频率从5GHz到5.2GHz的升频信号，但在接收信号中总是会出现0-15微妙左右的降频信号，如图片中的通道2所示（通道1是理想的发射信号），这很不正常，且接收信号的末端总是出现信号幅度为0的错误情况。附件是我根据FMCW Radar Waveform Based Range Calculation Using Time Trigger这一示例代码修改后的代码，但无法实现示例代码的准确接收的情况。请问我应该如何解决这个问题？十分感谢！

[Harsh]

Hi @伏伶,

From what I understand, you are using a USRP X310 with MATLAB to transmit and receive FMCW radar signals. You are seeing two issues: a strange down-chirp at the start of your received signal and the signal amplitude dropping to zero at the end.

These problems are common with SDR hardware and happen because:

• The transmitter hardware needs a brief moment to stabilize when it starts, which can cause initial frequency or phase distortion, often observed as a "chirp" or other transient artifacts at the start of the signal.
• There are small, unpredictable delays and buffering effects between transmit and receive, so the receiver may not capture the signal exactly as intended. This can result in the signal amplitude fading out or dropping to zero at the end, especially if the receive window does not fully cover the transmitted signal.

I hope this helps, thanks!