I have done two tests to transmit DC signal with NI-USRP 2920 and the parameters are as follow: common parameters: 1-carrier frequency: 200MHz 2-IQ Rate: 200kHz 3-Transmit Gain: 20dB for test-A: Transmit Signal: When the receive gain is 0dB, the received signal is When set the receive gain is 20dB, the received signal is for test-B Transmit signal: When the receive gain is 0dB, the receive signal is: I want to know why I cannot receive a signal similar to DC(that is, I expect that I will receive a DC plus a little noise). In the next project, I will use QPSK modulation, but the phase flip result（that is, the transmited signal don't have negative part but the received signal do）shown above makes me upset. Can I do something to help transmit in QPSK successfully? Thx!

USRP Software Radio

transmit DC signal but receive signal unexpected, why?

I have done two tests to transmit DC signal with NI-USRP 2920 and the parameters are as follow:

common parameters:

1-carrier frequency: 200MHz

2-IQ Rate: 200kHz

3-Transmit Gain: 20dB

for test-A:

Transmit Signal:

When the receive gain is 0dB, the received signal is

When set the receive gain is 20dB, the received signal is A-2-zoom in.png

for test-B

Transmit signal:

When the receive gain is 0dB, the receive signal is:

B-1-zoom in.png

I want to know why I cannot receive a signal similar to DC(that is, I expect that I will receive a DC plus a little noise).

In the next project, I will use QPSK modulation, but the phase flip result（that is, the transmited signal don't have negative part but the received signal do）shown above makes me upset. Can I do something to help transmit in QPSK successfully?

Thx!