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From: | Marcus D. Leech |
Subject: | Re: [Discuss-gnuradio] Problem with USRP! |
Date: | Sun, 08 Apr 2012 18:14:02 -0400 |
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It doesn't matter where you put your antenna... Ask yourself a fundamental question: When you assign both a receive chain and a transmit chain to the same antenna port in a flow-graph, which one gets access? How can you transmit and receive with the same frequency with the same antenna without jamming the receiver? Take the time to understand these issues before you do something that will damage the receiver LNA's.Insert a unpacked-to-packed block between your vector source and the modulator. bits per chunk = 1. See if this produces what you would expect.I also strongly suggest that you simulate these by looping the output of the mod to the input of the demod. This removes the USRP as a variable until you get a better understanding of how these blocks are working.-John
John:Based on the flow-graph they showed, they're using two different USRP -- one for RX one for TX.
On 04/08/2012 02:54 PM, huzaifazafar108 wrote:Dear John, Waiting for your response...And the reason for using TX/RX is that we connected the antennas on TX/RXports on the daughtercard (in both transmitter and receiver). Thanks, Huzaifa John Malsbury wrote:A few more things: 1) You have both the receive and transmit portions assigned to TX/RX.This only works if you run in half-duplex mode and stop streaming to theUSRP. This is not the case. 2) Note the difference between sample rate, symbol rate, and bit rate. symbol_rate = sample_rate / samples_per_symbol bit_rate = sample_rate/bits_per_symbol I think there are issues with packing/unpacking of bits. The requirements for packing and unpacking aren't completely consistent across the mod/demods within GNU Radio. Let me experiment real quick and get back to you. -John On 04/08/2012 02:34 PM, huzaifazafar108 wrote:Dear Marcus,I truly appreciate your prompt reply. However, I am not sure what shouldIput in the 'modulus' field of the block. By hit and trial, wrong outputsare emerging. Please guide. Best Regards, Huzaifa Marcus D. Leech wrote:Well, you're using DPSK, but not using a differential encoder on the TXWe just removed the throttle blocks and the same problem remains. Please let us know how to achieve symbol synchronization.side, nor a differential decoder on the RX side.huzaifazafar108 wrote:Dear John,Thank you for such a prompt reply. Okay, we will remove the throttleblocks just now. But can you guide us how to achieve symbol synchronization then? Best Regards, Huzaifa John Malsbury wrote:You do not need to use throttles when using a UHD sink/source, because the device provides timing for the flowgraph.Remove the throttles and try again. If you still see the failure I'dsay you are not achieving symbol sync. -John On 04/08/2012 01:58 PM, Huzaifa Zafar wrote:Dear all, I am working with 3 people on a project involving GNU Radio and USRP1. We have tried to implement a simple point to point digital communication system in GRC involving DQPSK modulation. Using a vectorsource we are sending a finite stream of zeros and ones (the vector source has Repeat set to yes). On the receiver side, what we receive is really very strange: The same stream of zeros and ones, but with extra zeros in between our actual data. For example, we send three ones and three zeros, but what we receive is a one followed by seven zeros, another one followed by seven zeros, another one followed by seven zeros, and then a zero followed by seven zeros e.t.c. We triedto experiment more by using the 'KEEP 1 in N' block and the'DECIMATING FIR FILTER', but things are not working out the way theyshould.I am also attaching a snapshot of the .grc file for your reference. Please tell us the reason why these extra zeros are present between our data bits, and the way to combat this effect (remember that thedecimating fir filter and keep 1 in N block are not showing the desired output). Any kind of help is appreciated in advance. -- Huzaifa Zafar _______________________________________________ Discuss-gnuradio mailing list address@hidden https://lists.gnu.org/mailman/listinfo/discuss-gnuradio_______________________________________________ Discuss-gnuradio mailing list address@hidden https://lists.gnu.org/mailman/listinfo/discuss-gnuradio-- Marcus Leech Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org _______________________________________________ Discuss-gnuradio mailing list address@hidden https://lists.gnu.org/mailman/listinfo/discuss-gnuradio_______________________________________________ Discuss-gnuradio mailing list address@hidden https://lists.gnu.org/mailman/listinfo/discuss-gnuradio_______________________________________________ Discuss-gnuradio mailing list address@hidden https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
-- Marcus Leech Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org
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