[Discuss-gnuradio] Transmit and Received Signals are Different

[Frederick Lee]

HI,

I am currently using two USRP N210 rev4 with a RFX2400 
daughter board and a VERT2450 antenna on each. I am having trouble 
transmitting a signal between the two USRPs even though they are right 
next to each other. 

On the transmitting flowgraph, I have a signal source sending a 
square wave at 1kHz with an amplitude of 100m connected to a USRP sink. On
 the receiving flowgraph, I have a USRP source multiplied with a complex
 cosine to shift the signal to baseband. Then I use a lowpass filter 
before sending to a scope sink or fft sink.

Whenever I use the scope sink to look at the incoming signal, it 
looks nothing like the square wave I am sending. It sometimes looks like
 a sine wave with a frequency other than 1kHz, or it looks something like the 
picture titled received_signal.png ( I only showed one of the lines 
because it was too cluttered with both of them ). When I send a cosine 
or a constant signal, I receive a sine on the scope, but the amplitude 
jumps a little and the frequency jumps up and down one or two kHz. 

I also wanted to know what happens to the signal in the RFX2400 
daughterboard and what the FPGA does to the signal. I think I read 
somewhere that the FPGA converts the signal to baseband, but I was not 
sure if that is true. I have attached the flowgraphs used for transmitting and receiving.

I appreciate any help,

Frederick

flowgraphs.zip
Description: Zip archive

received_signal.png
Description: PNG image