# How to show the internal clock on the flowgraph

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.

Thanks

Manuel

Hi Manuel,

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

Best regards,
Marcus M?ller

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

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

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.
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

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