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Re: [Discuss-gnuradio] Frequency Hopping/ center frequency /time

From: George Nychis
Subject: Re: [Discuss-gnuradio] Frequency Hopping/ center frequency /time
Date: Tue, 8 Dec 2009 12:05:27 -0500

On Tue, Dec 8, 2009 at 6:43 AM, Hanno Jung <address@hidden> wrote:
Hi out there,

I have several questions on Frequency Hopping.

I'm trying to send a constant with the *_siggen.py files on different frequencies in short intervalls.
Because those frequencies are spread over a band of 25MHz I need to change the center frequency of the board very fast(within micro seconds).

Now the question.

Is the usrp1/2 capable of this via the functions in python? How much time does the usrp need to change the center frequency?

I have read a few articles abut the minimal available time interval on desktop pcs. On ubuntu (hardy) there is a file called /usr/src/linux-Headers-2.6.24-25/kernel/Kconfig.hz where I can adjust the "Timer Interrupt Frequency Configuration" which allows 1000Hz which represents 0.001 seconds. (important for python timer functions)

Now the question.
Is this 0.001 s limit really the shortest time span available for this pc? It seems to be too long.
Is there an other possibility to send ~8 carriers distributed over a bandwitdh of 25MHz without preprocessed data?
Realtime/Frequency Hopping (tH=~several micro seconds)

I once looked in to this, and I believe that Matt once told me it takes ~200us for a daughterboard (I think it might have been RFX2400) to lock to a new frequency.  You can always set your bandwidth to a larger range and then transmit at different offsets within that range.

- George

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