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Re: [Discuss-gnuradio] Tune UHD - as fast as possible

From: Andrew Davis
Subject: Re: [Discuss-gnuradio] Tune UHD - as fast as possible
Date: Fri, 10 Feb 2012 10:23:50 -0500


Is the current API, i'm not sure how it gets to python world, but it looks like you can still call it with just the frequency.

Also it there any reason your doing this with GRC and not python?

On Fri, Feb 10, 2012 at 4:14 AM, Marius Ciepluch <address@hidden> wrote:
Hi Andrew,

thanks for the reply. I need the RF Frontend to change. I'm doing
measurements in order to find out how fast the RF Frontend can tune over
more than 25 MHz (on a USRP2). I need some exact data here, e.g. plots.
So in fact I want it to tune with no workarounds. And I want to see it
tune ;)

I pinpoint the Transceiver of the XCVR
(http://datasheets.maxim-ic.com/en/ds/MAX2828-MAX2829.pdf) in order to
get a down-scaled frequency.  I want to set a new frequency. An then I
want to plot how long it takes the device to issue the change. That's
UHD Device driver command + Ethernet latency + FPGA reaction.

My problem is, that I know of no way to tune it. Automatically changing
the center-frequency from GRC seems to be impossible to me.

- I found that. But
uhd.tune_request(target_freq, dsp_freq=0,
dsp_freq_policy=uhd.tune_request.POLICY_MANUAL) tells me, that it cannot
be evaluated in GRC. Variables set of course. I guess the constructor
changed, but there's no docu here.

- I can use a WX GUI slider, but I need an automated change. Actually a
switch between 50 and 75 MHz (so that my Oscilloscope copes with that).
Here I use the WBX. My overall goal is to understand more about the

So if someone knows how I can implement a callback or a polling function
to make the device tune for real, but as fast as possible, that'd be
very helpful.


On 02/09/2012 10:41 PM, Andrew Davis wrote:
> self.uhd_usrp_sink_0.set_center_freq(self.freq, 0) will take forever, the
> whole front end has to re-settle. How far are you moving the center
> frequency? If it's less than 50MHz you could change the sin signal
> frequency. You could even hook up a Frequency modulator and change the
> frequency continually and with absolutely no delay.
> On Thu, Feb 9, 2012 at 7:02 AM, Marius Ciepluch <address@hidden>wrote:
>> Hi!
>> I have put a Flow-Graph together, which is quite simple:
>> Sine Signal -> USRP2 UHD
>> Now I want to change the center-frequency as fast as possible.
>> My initial idea was a while True loop and to issue the
>> self.uhd_usrp_sink_0.set_center_freq(self.freq, 0) command from Python.
>> This does not work. It remains at the initial frequency.
>> Do you use the Function Probe block in GRC? Or is there any other way to
>> make it tune without ending the Flow-Graph?
>> Best,
>> Marius
>> _______________________________________________
>> Discuss-gnuradio mailing list
>> address@hidden
>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

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