Help on "easy" digital TX/RX

As to introduct me, im very new to GnuRadio and the general topic of
However, i have a project in which i should implement a very basic way
sending packets. This given packet format has a constant preamble and a
constant length of appended databits. For detecting those out of a
etc. ive already written a working matlab script, now im stuck at the
GnuRadio side.
As a simple Presentation it would be enough to save a captured bitstream
from GnuRadio to harddrive which i later load in Matlab and send it
my script.

So my question is, how can setup the most easily a one way tx/rx
between 2 SDR’s, without any packet format or, which simply gives me the
received bits? My basic idea is like that:
I simply cant get it working at all. It would be too kind if somebody
give me some kind of introduction how to handle that.


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You have a few options. You can build a digital tx/rx in GRC, run an
example like, etc. I’ve also created a set of examples with a
libraby called pre-cog, which you can see here:

An updated url to the pre-cog github pages:

If you do use pre-cog, feel free to send any questions. It’s a
work-in-progress and the documentation may not explain everything…


Thank you for the advising! That looks like something what i could use.
I just came up with another question:
I simply tried to simulate a DPBSK Path with noise, loaded from a file
sinked to a file. Between Demod and Sink i placed a “Pack K Bits” with
But my received data just contains 0’s! It has the right length, but
zeros… Any ideas anyone?

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I now have 2 new problems :frowning:

  1. I have a random source hooked to a Modulator and then to USRP. From
    same device i listen at the same Frequency. But since the antennas are
    a few cm’s away, the constellation graph is completely diffuse and the
    points are anywhere, there arent any fixed points noticeable. Do I have
    change something at the gain or add something?
  2. How can i differentiate if there is a signal receiving or just some
    background noise. I mean if i put the Demodulator directly after the
    and stream it to file, then of course ill mostly get just random

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On 01/14/2013 02:56 PM, Hanz wrote:


Few tips, the modulator tags packed bytes, so the random source should
be [0, 256)

The modulator produces amplitude 1.0 samples. You will want to scale
these down as fullscale can clip. Either multiply constant block or
fullscale stream arg in UHD block:

Put the output of the modulator on a the FFT plotter. You should see the
response of the matched filter.