Tom,
some pointers:
- I recommend using timed streaming for both Tx and Rx. You will get a more
deterministic time offset.
- I think you're not accounting for phase offsets as well as time offsets.
Your two signals do look similar -- maybe plot the envelope instead of the
real part. Also, you can play around with gain settings to get a better
amplitude alignment.
- Looping back into the same daughterboard means you need to deal with
crosstalk. If you're just playing around, you might be fine but in general,
if there's leakage from the Tx channel to the Rx channel, it will interfere
with the signal received through the cable.
--M
On Wed, Dec 11, 2024 at 12:58 PM Q W via USRP-users <
usrp-users@lists.ettus.com> wrote:
> Hi there,
>
> I just started using UHD Python API to implement a simple
> transmission-reception experiment on an Ettus X310. I have a UBX 160
> daughterboard installed on slot B, with its TX (TX/RX port) connected to RX
> (RX2 port) directly using a SMA cable and a 30dB attenuator. I plan to
> transmit a sequence of waveforms from TX/RX port and to see the waveforms
> received at the RX2 port. Ideally the two waveforms should be highly
> similar with some time shift in between, but the received waveforms turned
> out to be not quite right (see the diagram below, the upper diagram shows
> the real part of the transmitted waveform and the lower, the real part of
> the received.).
> [image: Inline image]
>
> Some of the parameters are defined as following:
> duration = 10 # second, the time length of the transmitter sending the
> waveforms
> centre_freq=1e8
> sample_rate=200000
> num_samples=200000 # number of samples to be collected by the receiving
> side.
> gain_tx=0 #dB
> gain_rx=20
>
> USRP is defined as:
> usrp = uhd.usrp.MultiUSRP()
> usrp.set_tx_subdev_spec(uhd.usrp.SubdevSpec("B:0"))
> usrp.set_tx_antenna("TX/RX")
>
> usrp.set_rx_subdev_spec(uhd.usrp.SubdevSpec("B:0"))
> usrp.set_rx_antenna("RX2")
> usrp.set_rx_bandwidth(sample_rate, 0)
>
> As the transmission and the reception happen at the same time, they are
> put in two separate threads, as below:
> threads = []
> rx_thread = threading.Thread(target=receive_data, args=(usrp, num_samples,
> centre_freq_rx, sample_rate, gain_rx))
> threads.append(rx_thread)
> rx_thread.start()
> tx_thread = threading.Thread(target=usrp.send_waveform, args=(tx_signal,
> duration, centre_freq_tx, sample_rate, [0], gain_tx))
> threads.append(tx_thread)
> tx_thread.start()
>
> Here the function, receive_data() in the first thread, is a user-defined
> (by me) function, receiving samples using the uhd provided method,
> usrp.recv_num_samps() and saving the samples to a .txt file. A little more
> on the data format saved in the file, I used np.savetxt() function to save
> the samples (a numpy array) to a text file. As the numpy array has a data
> type of np.complex64, the real and imaginary of the samples are saved in
> the same file in the format of np.float32. I can confirm that 200000
> complex samples were collected in the file saved, which verifies (partially
> at least) that data format didn't go wrong.
>
> I have been working on this script for a whole day, but couldn't fix it. I
> suspect I didn't configure the usrp variable correctly. Any suggestions
> would be appreciated.
>
> Kind regards,
> Tom
>
>
>
>
>
>
>
>
>
>
> As the transmission and reception happen simultaneously, the Python scritp
>
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