Problems with signal reception (BladeRF-x40 , GNUradio)

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raul8883
Posts: 1
Joined: Sat Jul 02, 2022 6:37 am

Problems with signal reception (BladeRF-x40 , GNUradio)

Post by raul8883 »

Hi everyone, I am having problems when I receive signals using two SDRs (BladeRF - x40), one to transmit and one to receive (I know I can transmit and receive using 1 SDR, but I need the complete schematic transmitter, receiver), the problem is the following, I have a complex signal , with the following values:
in-phase component (i(t)) tx = Ac * x(t)
quadrature component (q(t)) tx = 0
Vy (t) tx = i(t) + j q(t)
TX
https://user-images.githubusercontent.c ... 5334d6.png

I send this signal to the channel and therefore it is received by the SDR receiver.
What I receive in the reception is not similar to what I transmitted, because of a tone appears both in its component in phase and in quadrature, by making q(t) rx /≈ q(t) tx /≈ 0.
RX
https://user-images.githubusercontent.c ... a208c7.png

For a better compression, I will transmit the following signal x(t) = 0 (equivalent to i(t) tx = 0, q(t) tx = 0), so in theory in reception it would only have noise, but this is not the case.
TX
https://user-images.githubusercontent.c ... d62a73.png
RX
https://user-images.githubusercontent.c ... 9e1a86.png
When I use a single SDR to transmit and receive this does not happen, I don't know if this is due to some kind of synchronization, but with this problem I can not correctly classify the type of modulation.
BLOCK SDR Transmitter.
https://user-images.githubusercontent.c ... 8fbb7f.png
BLOCK SDR Receiver.
https://user-images.githubusercontent.c ... f5e1cf.png

This is what i am getting (Frecuency Domain) when i am transmitting a message with amplitude = 0 and both SDRs have gain equal to 0
https://user-images.githubusercontent.c ... 196646.png

When I increase the gain, that peak increases, in addition another peak appears symmetrical to that one with less amplitude
https://user-images.githubusercontent.c ... 1a82b3.png

This does not happen when I transmit and receive with the same sdr,
Could this be due to mismatches between both SDRs?

I need help to know how to make it not transmit and receive that unwanted signal.
Thank you very much in advance!
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