[Discuss-gnuradio] help -- how to implement transmitting periodic on/off tones
Hello: I have a USRP2 board and a WBX daughterboard. I am trying to implement a scheme where a single-tone sine wave (at frequencies between 1 kHz and 10 kHz) is transmitted intermittently. Specifically, time is divided into intervals, defined by the user on the command line, typically of values such as 200 ms or 500 ms or 1s. When invoked, the flow graph (the Python script) would transmit nothing (all zeros) during the first time interval, then transmit the tone during the second time interval, then transmit nothing (all zeros) during the third and fourth and fifth time intervals, then transmit the tone during the sixth time interval, then transmit nothing (all zeros) during the seventh time interval, and then stop and end. How in the world could I implement this? I feel like it'd be hard to do, but maybe it's actually easy. Would I need to use a timer in Python to set what gets transmitted at the start of each interval duration? Any help would be very much appreciated, as I am still somewhat new to GNU Radio and Python. Thanks for your help, everyone. Steve McMahon ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] help -- how to implement transmitting periodic on/off tones
On Mon, Nov 29, 2010 at 12:42:38AM -0800, Steve Mcmahon wrote: Hello: I have a USRP2 board and a WBX daughterboard. I am trying to implement a scheme where a single-tone sine wave (at frequencies between 1 kHz and 10 kHz) is transmitted intermittently. Specifically, time is divided into intervals, defined by the user on the command line, typically of values such as 200 ms or 500 ms or 1s. When invoked, the flow graph (the Python script) would transmit nothing (all zeros) during the first time interval, then transmit the tone during the second time interval, then transmit nothing (all zeros) during the third and fourth and fifth time intervals, then transmit the tone during the sixth time interval, then transmit nothing (all zeros) during the seventh time interval, and then stop and end. How in the world could I implement this? I feel like it'd be hard to do, but maybe it's actually easy. Would I need to use a timer in Python to set what gets transmitted at the start of each interval duration? Any help would be very much appreciated, as I am still somewhat new to GNU Radio and Python. Thanks for your help, everyone. Think of the on/off part as a control stream consisting of 1's and 0's. Generate the control stream, and multiple the control stream by the carrier stream. Don't try to start and stop the graph or anything like that from python. You can probably generate the control stream with a gr.vector_source_f([my-pattern], True) followed by a dumb interpolator that will just replicate values. my_pattern = [1, 1, 0, 0, 1, 0, ... ] interp_factor = 1000 # scale the pattern up in time to match signal ctrl_pattern = gr.vector_source_f(my_pattern, True) ctrl_interp = gr.interp_fir_filter_fff(interp_factor, interp_factor*[1.0]) signal = generate carrier mult = gr.multiple_ff() sink = something-downstream tb.connect(ctrl_pattern, ctrl_interp, (mult, 0)) tb.connect(signal, (mult, 1)) tb.connect(mult, sink) Eric ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] help -- how to implement transmitting periodic on/off tones
Think of the on/off part as a control stream consisting of 1's and 0's. Generate the control stream, and multiple the control stream by the carrier stream. Don't try to start and stop the graph or anything like that from python. You can probably generate the control stream with a gr.vector_source_f([my-pattern], True) followed by a dumb interpolator that will just replicate values. my_pattern = [1, 1, 0, 0, 1, 0, ... ] interp_factor = 1000 # scale the pattern up in time to match signal ctrl_pattern = gr.vector_source_f(my_pattern, True) ctrl_interp = gr.interp_fir_filter_fff(interp_factor, interp_factor*[1.0]) signal = generate carrier mult = gr.multiple_ff() sink = something-downstream tb.connect(ctrl_pattern, ctrl_interp, (mult, 0)) tb.connect(signal, (mult, 1)) tb.connect(mult, sink) One would think something like this would work, but I've noticed that even if you're sending 0's to your usrp sink, the transmitter still puts out some amount of power (plenty strong enough to be detectable via a spec-an). This power goes away if you disable the transmitter via software. Does anybody know anything about this phenomenon? -Steven ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] help -- how to implement transmitting periodic on/off tones
On 11/29/2010 01:35 PM, Steven Clark wrote: One would think something like this would work, but I've noticed that even if you're sending 0's to your usrp sink, the transmitter still puts out some amount of power (plenty strong enough to be detectable via a spec-an). This power goes away if you disable the transmitter via software. Does anybody know anything about this phenomenon? -Steven Slight LO leakage out of the mixer? -- Marcus Leech Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] help -- how to implement transmitting periodic on/off tones
Yes, LO leakage, more specifically DC imbalance in the I and Q channels; I assume you are using a daughter board with an IQ modulator? This is supposedly corrected for in the firmware, however, probably not done over temperature. You can probably tweak it by adding/subtracting a few LSB of DC offset to your I and Q samples. It's an iterative approach, tweaking until you minimize it. Won't be able to do better than what's spec'd in the data sheet though. I have never been able to get less than -60 dBc; not on URSP hardware but my own stuff. It's really only a problem in really wide-band modulation (e.g. spread spectrum) where your leakage poke above the modulation, or with tons of averaging and you are trying to hide your signal. Of course it's a problem for you, but best bet to blank off the buffer (or switch the T/R switch) to improve isolation. -- View this message in context: http://old.nabble.com/helphow-to-implement-transmitting-periodic-on-off-tones-tp30328518p30334344.html Sent from the GnuRadio mailing list archive at Nabble.com. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
