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I am relatively new to working with SDRs and GNURadio and I am attempting to generate a BPSK signal and transmit it through one USRP and receive and demodulate it on another USRP. I am using GNURadio and I am transmitting from an E310 to an N210 directly connected with a 30 dB attenuator.

Here are the flow graphs for my transmitter/receiver setup:

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When I implemented this transmitter/receiver in a single flow graph with no SDRs, it worked fine. However, when I try and use it with the SDRs I get some strange results in the constellation at the receiver end.

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From my simulations I expect to see the constellation points in two clusters on the x-axis. Running it through the clock sync and costas loop did not help. I have tried synchronizing the SDRs using an external reference signal but it didn't help. I also used an external synthesizer to send a BPSK signal to my receiver and got a similar constellation.

Any suggestions or ideas would be appreciated.

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