BPSK GNU radio companion/USRP help!

Dear GNU Society,

My team mate and I are trying to transmit a vector length of 1010110
which constantly repeats. We are trying to send the signal using BPSK
modulation/demodulation. For this we are using grc.

TX block parameters:
repeated bit vector source --> chunks to symbol --> rrc (interpolation:
400, gain: 10k, sample rate: 500kHz, symbol rate: 1, alpha, 1, #of taps:
22) --> usrp sink (interpolation: 512, frequency: 2.45GHz, gain: 0);
this is transmitted through the rf antenna connected to the USRP1 with
the daughter board rfx2400 with a frequency range of 2.4GHz-2.5GHz.

RX block parameters:
usrp source(decimation: 128, frequency: 2.44998GHz due to offset, gain:
30) -->agc (rate: 500kHz, ref.:1, gain:0, max gain:1) --> rrc
(decimation: 400, gain 1, sample rate: 500kHz, symbol rate: 1, alpha:
350m, taps: 22) --> costas loop (alpha: 20m, beta: 400u, max freq:
2.5G, min freq: 2.4G)–> M&M clock recovery (omega:2, gain omega:100,
mu: 500m, omega rel. limit: 100u) --> binary slicer.

Our symbol rate is: 250K, data rate: 500kHz, ADC rate: 64M, sps: 2. Our
program does not seem to be working. Please need any type of thought if

Also, we’ve tried running the RX and TX benchmark examples in the
following path in the GNU Radio source folder:


And ran the RX program only, using the command:

./benchmark_rx.py - f 2.45G

Once the RX program was running we received packets even without running
the TX program (benchmark_tx.py).
Which, I thought even if you don’t transmit any information you are not
actully sending any information you will still receive everything else
in your surroundings(noise, interference, other signals, etc.) Meaning
it should not be idle when not transmitting from one usrp to the second
Could someone correct me please whether my thoughts are correct or

Any incite on the cause of the problem will be appreciated.

RFX2400 daughterboards
HG2458RD-SM tri-band antenna (2.4 GHz to 5.8 GHz)

Any feedback is very much appreciated.

Thank you to anyone who chooses to participate in this times of

Our program does not seem to be working.
Please need any type of thought if possible!

First, please see this article on how to appropriately ask questions
of the mailing list:


Specifically the part titled “How should I format my message?”.

Secondly, does your program work if you take out the USRP and simply
connect your source and sink blocks together?

Though your path looks correct, I would check some of the parameters
you are using. For example, the costas loop probably takes in
relative frequencies, not specific ones (ie not 2.4G-2.5G) or the 500k
sample per symbol you are using for the RRC. Look at the code of
benchmark_rx and benchmark_tx in the digital examples folder to get an
idea of what a basic DBPSK system should look like.