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

From: Marius Ciepluch
Subject: Re: [Discuss-gnuradio] Tune UHD - as fast as possible
Date: Fri, 10 Feb 2012 10:14:38 +0100
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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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