# How to show the internal clock on the flowgraph

**URL:** <https://www.ruby-forum.com/t/how-to-show-the-internal-clock-on-the-flowgraph/234406>\
**Category:** GNU Radio\
**Created:** [March 2, 2015, 8:07pm UTC](https://www.ruby-forum.com/t/how-to-show-the-internal-clock-on-the-flowgraph/234406 "2015-03-02T20:07:56Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [March 2, 2015, 8:07pm UTC](https://www.ruby-forum.com/t/how-to-show-the-internal-clock-on-the-flowgraph/234406/1 "2015-03-02T20:07:56Z")

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Hi everyone,

I’m using a USRP B210 board, and I don’t know how to watch on the  
flowgraph the internal clock of the board, I need it to compare the time  
difference of two signals.

Please Help Meeeee.

Thanks

Manuel

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**Author:** ![Manuel\_David\_Lozano](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ce7236/32.png) [@Manuel\_David\_Lozano](https://www.ruby-forum.com/u/Manuel_David_Lozano)\
**Post date:** [March 2, 2015, 8:26pm UTC](https://www.ruby-forum.com/t/how-to-show-the-internal-clock-on-the-flowgraph/234406/2 "2015-03-02T20:26:28Z")

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Hi Manuel,

could you explain what you mean with “internal clock of the board”?

Best regards,  
Marcus M?ller

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**Author:** ![Manuel\_David\_Lozano](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ce7236/32.png) [@Manuel\_David\_Lozano](https://www.ruby-forum.com/u/Manuel_David_Lozano)\
**Post date:** [March 3, 2015, 2:00pm UTC](https://www.ruby-forum.com/t/how-to-show-the-internal-clock-on-the-flowgraph/234406/3 "2015-03-03T14:00:32Z")

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Hi Manuel,  
On 03/02/2015 08:38 PM, Manuel David Lozano Amezquita wrote:

> Hi Marcus, I know that the clock of the USRP b210 is 62MHz, but I need  
> to show it on the flowgraph to compare the phase of two signals.

I’m really confused. You _can_ configure the master clock rate, which is  
the rate at which the signal is sampled, to be up to 61.44MHz, but  
that’s neither the default nor 62MHz. There are several clocks in the  
B210, so maybe I’m missing something.

Where does that freuquency come from? What does it signify?  
Why do you need it to compare phases? Of what?

Best regards,  
Marcus M??ller

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**Author:** ![Manuel\_David\_Lozano](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ce7236/32.png) [@Manuel\_David\_Lozano](https://www.ruby-forum.com/u/Manuel_David_Lozano)\
**Post date:** [March 3, 2015, 2:19pm UTC](https://www.ruby-forum.com/t/how-to-show-the-internal-clock-on-the-flowgraph/234406/4 "2015-03-03T14:19:07Z")

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Hi Manuel,

your signal is sampled with a sample rate. You can now estimate the time  
shift in (fractional) samples, and calculate the “wall clock” time  
difference by dividing by the sampling rate.  
You, as a user, set the sampling rate that your device uses. The B210 is  
very flexible in respect to that.

Best regards,  
Marcus

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**Author:** ![Manuel\_David\_Lozano](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ce7236/32.png) [@Manuel\_David\_Lozano](https://www.ruby-forum.com/u/Manuel_David_Lozano)\
**Post date:** [March 6, 2015, 10:08am UTC](https://www.ruby-forum.com/t/how-to-show-the-internal-clock-on-the-flowgraph/234406/5 "2015-03-06T10:08:17Z")

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Hi Manuel,

On 03/05/2015 01:40 PM, Manuel David Lozano Amezquita wrote:

> Hi Marcus,
> 
> Now I have another question, How can I estimate the time shift in  
> fractional samples?, for example, I have a Cosine signal with  
> amplitude of 1 v, and 1 kHz, and I configure my sample rate in 1 MHz.  
> Then I transmit that signal, and some time later I receive it with  
> another antenna, so How could I determine the time difference of both?.  
> That is a question that seems to be central to your problem. I have some  
> approaches to answers, but explaining them in depth will take rather  
> long, and not explaining them won’t actually help you. Have a look at  
> what a cross correlation is; you should be able to understand what you  
> need to do rather quickly.
> 
> The objective is to measure the distance between the Tx antenna and  
> the Rx antenna, And I know that distance=velocity/time, I know the  
> velocity but I need the time that the signal spends from the Tx  
> antenna to ]Rx antenna.  
> Yep, classical radio ranging problem; have a look at existing radar  
> algorithms. Also bear in mind that the temporal resolution of your  
> system is given by Nyquist’s theorem, which leads you to $\delta t =  
> \frac{1}{f\_\text{sample}}$ in the complex case, to assess if your  
> application is feasible at all.
> 
> All the advices or tips that you could give me, I will appreciatte it  
> a lot.  
> In all honesty: what you’re having are basic signal processing  
> questions, and you should read a textbook on signal theory. GNU Radio  
> has a suggested reading page, which might give you a start[1].

Greetings,  
Marcus

[1] [https://gnuradio.org/redmine/projects/gnuradio/wiki/SuggestedReading](https://gnuradio.org/redmine/projects/gnuradio/wiki/SuggestedReading)