Problems with signal reception (BladeRF-x40 , GNUradio)

#1

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
image
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
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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
image
RX
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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.
image
BLOCK SDR Receiver.
image

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

image
image1236×234 52.1 KB

When I increase the gain, that peak increases, in addition another peak appears symmetrical to that one with less amplitude

image
image1230×244 104 KB

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!

#2

Have you tried either asking the people who make and sell the hardware, or people own and use the hardware ? https://www.nuand.com/support/

I’d try searching the hardware manufacturers website by plugging something like “site:nuand.com filetype:pdf bladerf” into any search engine.

1 Like
#3

Hello, first of all thank you very much for your answer.
Yes, I have been commenting on the problem in the developer’s official forums, but I do not receive a response or perhaps the response is received too late.

#4

My bladeRF 2.0 micro xa5 will not operate at any bandwidth of less than about 1 MSPS. Perhaps, yours is erroring on the 150 KSPS and actually using some default value.

P.S.
I took a look at the BladeRF driver and it picks the actual bandwidth used from a table - taking the closest value to that requested.

#5

+1. BladeRF is not a MyriadRF project and you’d be better asking in the appropriate forum.

#6

Hi @raul8883,
Did you end up finding a solution to this problem? I am currently working on a transceiver and need to use two bladeRF SDR’s. The signal I received also shows the same sort of response yours does - my signal seems to be “riding” on a sine wave noise floor. Thanks.

#7

I saw “signal seems to be “riding” on a sine wave noise floor”. I think that it was when the receiver port was not connected to an antenna.

#8

Hi, thank you for your response. This effect is happening while I have the antenna connected. The moment I disconnect the transmitter side the noise returns to 0 again