Re: [Discuss-gnuradio] Scanning desired frequenies

[Marcus Müller]

Samples are what comes out of your USRP, and what you process in GNU Radio.

What a tag is, how blocks work, and how you can write your own is all covered in the guided tutorials; I'd recommend reading those from first to 6, because that will cover all these topics, including dealing with Hardware like the USRP.

Best regards,
Marcus

On 06/15/2015 10:49 PM, Ashraf Younis wrote:

I'm sorry but this is all too much. I need some help breaking this process down. 

What do you mean by samples, Is that the frequency list?

My first block is reading the data from the file, and has an input for tx_tune?

What is a tag?

When I do all this I will run it in GRC, correct?

On Mon, Jun 15, 2015 at 12:31 PM, Marcus Müller <address@hidden> wrote:

Hi Ashraf,

thanks for the nice words and the detailed problem description.

Yes, I think there are ways to achieve what you want; you will have to write a few GNU Radio blocks, but I think it's possible to do after lecture of the GNU Radio guided tutorials [1]; if you encounter any obstacles, the mailing list probably will have an open ear for you :)

You could write your own block that passes through samples, and controls the USRP. For starters, that could be done in python, if that feels more familiar to you than C++. It will have to be a general block.

As a first step, that block would simply wait for a tx_time tag coming in. That tag value contains the time at which tuning happened.
Use that time to calculate the time at which the next tuning should occur.
Give your block the ability to call your usrp_source's set_command_time() with that time.
Use message passing to issue the tuning command [2].
After each tag, pass a fixed amount of samples <= (inter_tune_time*sampling rate), and just consume the rest, until the next tag appears. Pass through the rx_freq tag to the first passed sample.

Connect your block's input to your usrp_source's output, and message_connect your block's message output to the usrp_source's message input.

Connect the output of your block to a stream to vector; connect that to whatever processing you want to do. For example, you can do an FFT.
After the FFT, you could attach another block that you'd write yourself, that would take the rx_freq tag again,and based on that, would for example put the FFT vector into the right position in an array of FFT vectors.

Best regards,
Marcus

[1] https://gnuradio.org/redmine/projects/gnuradio/wiki/Guided_Tutorials
[2] http://gnuradio.org/doc/doxygen/page_uhd.html#uhd_command_syntax

On 06/15/2015 06:10 PM, Ashraf Younis wrote:

I have been trying to make my NI-B200 scan frequencies that I have in a text file for a couple days now. I was introduced to this mailing list through the GNU website and it has helped me alot these past few day, Thank you all, but I haven't completed my task yet so I'm going to be as specific as possible with what I need help with and with what I have been doing. 

I have a list of about 1000+ frequencies and I need to scan all of them with my NI-B200 and record their power(dB). I am currently using using usrp_spectrum_sense.py (https://github.com/gnuradio/gnuradio/blob/master/gr-uhd/examples/python/usrp_spectrum_sense.py) to scan the frequencies but it scans a range and not the specific frequencies I want so I made my own py file that simply loop the execution of usrp_spectrum_sense.py until the end of the list. It is a very crude way of going about things. Is there a better, much cleaner way I can accomplish my goal?

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