On 07/19/2012 03:30 PM, Frederick Lee wrote: > 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. >
Perhaps you are seeing a small frequency offset between RX and TX. I recommend experimenting a little more in simulation: * What happens you pass the same square wave through that low pass filter you mentioned. Whats it look like? * What happens when you apply a small frequency shift to the square wave? I recommend using the channel model block for this. -josh _______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
