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RE: [Discuss-gnuradio] Question about latency

From: Firas Abbas
Subject: RE: [Discuss-gnuradio] Question about latency
Date: Thu, 2 Apr 2009 08:25:29 -0700 (PDT)


> On Thu, 4/2/09, Matigakis Emmanouil <address@hidden> wrote:

> Hello,
> I did tried to increase the sampling rate and the delay
> went up to 100ms. I was getting a lot of Uo on the screen though from 
> the program. The block I've made that does the
> processing stores the waveform it receives in a file so I can look at it 
> from Matlab.
> I think what I'm trying to do is very difficult if at all possible with > 
> flowgraphs. So I will  try to use in-band signaling code. Is there > 
> something similar to gr-howto-write-a-block for using mbloks?
> Thanks
> Manolis

If you are trying to do just an RF repeater (digitally connecting TX IF and RX 
IF ), I don't think the time is much as 100msec with 4MHz. There is something 
wrong. I suggest to you to use BasicRX and Basic TX in the first.

If you want to measure the delay from end to end , I suggest the following idea 
(I didn't implement and tried it, it just came on my mind while reading your 

Connect the output of Basic TX to the input of basic RX through 20 dB 
attenuator. Start grc, connect a saw tooth signal generator to usrp sink. 
Connect usrp source to oscilloscope graphical sink (channel A). For the same 
scope sink, connect the saw tooth source to its other channel (channel B). You 
should now see two saw tooth signals one that send to TX and the other is the 
received RX. Vary saw tooth frequency and measure the delay between the start 
of these two signals. This will be the end to end latency. Of course it will 
depend you your PC speed and its OS.

Let me know if it works for you.

Best Regards,


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