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Re: FMCW GNU Radar Toolbox

From: Pham Van Dung
Subject: Re: FMCW GNU Radar Toolbox
Date: Fri, 9 Jul 2021 09:35:29 +0200

Yes, I use it for another project which is a pulse FMCW radar project

In this project, we need an LFM with receiving time (dead-time) for testing the function of the radar (transmitter and receiver etc..)

Do you have any tutorial to modify the block of GNU Radio? I am a hardware guy so it may take some time to implement this work so I would appreciate it if you can help me how to modify it

Thank you very much

On Thu, Jul 8, 2021, 18:07 Alex Batts <battsalex99@gmail.com> wrote:
What on the other device are you trying to measure? Are you simply attempting to see if you can receive a signal, or are you trying to receive information of some kind?

Generating an LFM signal is no problem, and modifying the source code is a good way to go if that's all you want to do. You are right though about the 56 MHz bandwidth, and the sample rate may affect your chirp repetition frequency.



On Thu, Jul 8, 2021 at 11:20 AM Pham Van Dung <dungdkt27@gmail.com> wrote:
Thank Alex for your answer,

For the second question, I will not design a pulse doppler radar with a linear FM pulse. But I wonder that I could generate an LFM signal (to measure another RF device at 1GHz) using Ettus B200?

Due to the limit of the hardware capabilities, I think I can only generate an LFM with a maximum ~ 56 MHz sweep bandwidth (if possible).

My approach is the modification of the source code of the FMCW block using OutOfTreeModules with gr_modtool, 

In which I will add the deadtime at the end of each FMCW pulse but I think I will not trade with my time to do this problem because I have already another solution :D

Again, I appreciate your help and time in advance

Vào Th 5, 8 thg 7, 2021 vào lúc 16:16 Alex Batts <battsalex99@gmail.com> đã viết:

It has been a while since I used the FMCW block in the Radar toolbox, but from what I can remember, the three samples sections are defining the percentage of the signal you want distributed in each of those sections. For example, if you want 50% of your signal to be CW, and 50% to be up-chirp, put an equal number of samples in the Samples CW and Samples up-chirp sections. The number of samples combined with your sample rate and frequency sweep will determine the slope of the fm chirp.

There is also a VCO block I'm pretty sure that you can use for more customizable fmcw radar.

For your second question, why do you want to add a dead time? My guess would be because you are trying to do pulse doppler of some sort, but if not please explain because I would definitely be interested in knowing what you are attempting to do! If you are trying to do a pulse doppler radar with a linear fm pulse compression, unfortunately, there isn't much functionality within GNU Radio for that kind of thing, and SDRs aren't great for pulse doppler right now. In a few years' time they will, but most affordable SDRs just don't have the hardware capabilities necessary. FMCW is the way to go for SDRs because of low peak power needed and because timing is not as necessary for range disambiguation, which is nice because of the low sample rates of most SDRs. 

I am not sure you can implement a dead-time within the FMCW signal generator block, and am not sure that gr-radar has that capability. However, if you still want to implement a dead-time, you could write a custom block (GNU Radio has extensive tutorials on how to do this, and only requires basic knowledge of yaml and c++). I would do something like, generate a sine wave, and while the sine wave is above a certain threshold, send the fmcw signal through, else, send a constant 0 through. You would have to play around with the threshold to get the proper duty cycle and play around with the frequency of the sine wave to make sure you are staying in sync with the signal generator, but that is one idea on how I would do it off the top of my head.

Can you give me more information on the project and/or what your goals are? It would help me give more specific advice as opposed to shooting blindly.

Thank you,


On Thu, Jul 8, 2021 at 5:44 AM Pham Van Dung <dungdkt27@gmail.com> wrote:
Hello all,
I want to make an FMCW signal generation with GNU Radar toolbox and Ettus B200
I saw that you have several examples in https://github.com/kit-cel/gr-radar/tree/master/examples/simulation, but I do not understand the following parameters of the FMCW block
- Samples CW
- Samples up-chirp
- Samples down-chirp
- Frequency CW
Second question, if I want to modify the block (I want to add dead-time at each pulse of FMCW), How can I do it?
I appreciate your help and time


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