Re: [Discuss-gnuradio] The shortest pulse length
Thanks for the advice. I don't think that's my only problem though. My vector is currently supposed to produce 2500 samples. This combined with an interpolation factor of 512, should give me 10 msecs of signal. Have I calculated this correctly? Also, I'm using the gr.modulation block to make the signal, but if it is producing complex output, does that mean I'm actually sending 5000 samples? At the moment, sending my 2500 samples produces an output only 1 msec long. Regards Lance - Original Message From: Eric Blossom [EMAIL PROTECTED] To: seph 004 [EMAIL PROTECTED] Cc: David Scaperoth [EMAIL PROTECTED]; discuss-gnuradio@gnu.org Sent: Friday, March 2, 2007 7:06:06 PM Subject: Re: [Discuss-gnuradio] The shortest pulse length On Fri, Mar 02, 2007 at 12:41:40AM -0800, seph 004 wrote: I am only using 1 daughterboard. Sorry about the duc0 = 0 inclusion. It's something I neglected to remove when I was editing the original file. I don't think it should have any effect on what I am seeing though. I set the duc frequency to 0 because I wanted to transmit at baseband. I've already built the signal I want in the gr.vector, I just want the daughterboard to pass it as is. I've managed to do that with usrp_siggen.py. By setting the -f option to 0 and the -w option to some frequency, I get a waveform of the -w frequency at the daughterboard output. I'm pretty sure (0, 0) is TXA, and (1, 0) is TXB. My waveform does appear at the TXB output when I run the script. The problem is the pulse duration I'm seeing is much shorter (about 1/10) than what I expect. Regards Lance Unless the total number of samples comes out to a multiple of 128, some will left in the host buffer and not transmitted across the USB. Try padding your vsource data with zeros to a multiple of 128. Eric - Original Message From: David Scaperoth [EMAIL PROTECTED] To: seph 004 [EMAIL PROTECTED] Cc: discuss-gnuradio@gnu.org Sent: Thursday, March 1, 2007 7:15:36 PM Subject: Re: [Discuss-gnuradio] The shortest pulse length On 3/1/07, seph 004 [EMAIL PROTECTED] wrote: This is what I did: def build_graph (): nchan = 1 interp = 512 duc0 = 0 duc1 = 0 fs = 250e3#2nd sample rate between usb and dac max_dev = 32e3 #1st sample rate divided by 4 (1st = 2nd sample rate) gain = 16e3 k = 2 * math.pi * max_dev / fs vec1 = Numeric.arange (0.624, 0.656, 0.128) vsource = gr.vector_source_f(vec1, False) fmmod = gr.frequency_modulator_fc (k) amp = gr.multiply_const_cc(gain) fg = gr.flow_graph () u = usrp.sink_c (0, interp, nchan) tx_subdev_spec = (1, 0) #usrp.pick_tx_subdevice(u) m = usrp.determine_tx_mux_value(u, tx_subdev_spec) u.set_mux(m) subdev = usrp.selected_subdev(u, tx_subdev_spec) subdev.set_enable(True) sample_rate = u.dac_freq () / interp u.set_tx_freq (0, duc0) u.set_tx_freq (1, duc1) Yahoo! Music Unlimited Access over 1 million songs. http://music.yahoo.com/unlimited___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] The shortest pulse length
Thanks for the reply. I mentioned in my response to David's message that I'm purposefully setting the duc frequency to 0 to transmit at baseband. Is using .tune to do this better than the set_freq method even if I don't want duc to do anything to the signal? Regards Lance - Original Message From: Eric Blossom [EMAIL PROTECTED] To: David Scaperoth [EMAIL PROTECTED] Cc: seph 004 [EMAIL PROTECTED]; discuss-gnuradio@gnu.org Sent: Thursday, March 1, 2007 11:32:45 PM Subject: Re: [Discuss-gnuradio] The shortest pulse length On Thu, Mar 01, 2007 at 12:15:36PM -0500, David Scaperoth wrote: On 3/1/07, seph 004 [EMAIL PROTECTED] wrote: This is what I did: def build_graph (): nchan = 1 interp = 512 duc0 = 0 duc1 = 0 fs = 250e3#2nd sample rate between usb and dac max_dev = 32e3 #1st sample rate divided by 4 (1st = 2nd sample rate) gain = 16e3 k = 2 * math.pi * max_dev / fs vec1 = Numeric.arange (0.624, 0.656, 0.128) vsource = gr.vector_source_f(vec1, False) fmmod = gr.frequency_modulator_fc (k) amp = gr.multiply_const_cc(gain) fg = gr.flow_graph () u = usrp.sink_c (0, interp, nchan) tx_subdev_spec = (1, 0) #usrp.pick_tx_subdevice(u) m = usrp.determine_tx_mux_value(u, tx_subdev_spec) u.set_mux(m) subdev = usrp.selected_subdev(u, tx_subdev_spec) subdev.set_enable(True) sample_rate = u.dac_freq () / interp u.set_tx_freq (0, duc0) u.set_tx_freq (1, duc1) Are you trying to use one daughter boards(nchen=1)? Why did you set duc0 = 0? that means your frequency will not be set at all. You do not need to do set_tx_freq() twice if you are using one daughter board. you only need : u.set_tx_freq (0, duc0) where duc0 is some frequency. Also, if you are using the basic daughterboards, you need to make sure that you have the output connector connect to TXA not TXB (according to your tx_subdev_spec) Hope this helped. David Lance, you really want to be using tune, not set_tx_freq. tune knows about all the daughterboards and does the right thing to split the work between the digital upconverter and the RF front end (if any). Take a look at fm_tx4.py or fm_tx_2_daughterboards.py Eric TV dinner still cooling? Check out Tonight's Picks on Yahoo! TV. http://tv.yahoo.com/___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] The shortest pulse length
On Fri, Mar 02, 2007 at 12:41:40AM -0800, seph 004 wrote: I am only using 1 daughterboard. Sorry about the duc0 = 0 inclusion. It's something I neglected to remove when I was editing the original file. I don't think it should have any effect on what I am seeing though. I set the duc frequency to 0 because I wanted to transmit at baseband. I've already built the signal I want in the gr.vector, I just want the daughterboard to pass it as is. I've managed to do that with usrp_siggen.py. By setting the -f option to 0 and the -w option to some frequency, I get a waveform of the -w frequency at the daughterboard output. I'm pretty sure (0, 0) is TXA, and (1, 0) is TXB. My waveform does appear at the TXB output when I run the script. The problem is the pulse duration I'm seeing is much shorter (about 1/10) than what I expect. Regards Lance Unless the total number of samples comes out to a multiple of 128, some will left in the host buffer and not transmitted across the USB. Try padding your vsource data with zeros to a multiple of 128. Eric - Original Message From: David Scaperoth [EMAIL PROTECTED] To: seph 004 [EMAIL PROTECTED] Cc: discuss-gnuradio@gnu.org Sent: Thursday, March 1, 2007 7:15:36 PM Subject: Re: [Discuss-gnuradio] The shortest pulse length On 3/1/07, seph 004 [EMAIL PROTECTED] wrote: This is what I did: def build_graph (): nchan = 1 interp = 512 duc0 = 0 duc1 = 0 fs = 250e3#2nd sample rate between usb and dac max_dev = 32e3 #1st sample rate divided by 4 (1st = 2nd sample rate) gain = 16e3 k = 2 * math.pi * max_dev / fs vec1 = Numeric.arange (0.624, 0.656, 0.128) vsource = gr.vector_source_f(vec1, False) fmmod = gr.frequency_modulator_fc (k) amp = gr.multiply_const_cc(gain) fg = gr.flow_graph () u = usrp.sink_c (0, interp, nchan) tx_subdev_spec = (1, 0) #usrp.pick_tx_subdevice(u) m = usrp.determine_tx_mux_value(u, tx_subdev_spec) u.set_mux(m) subdev = usrp.selected_subdev(u, tx_subdev_spec) subdev.set_enable(True) sample_rate = u.dac_freq () / interp u.set_tx_freq (0, duc0) u.set_tx_freq (1, duc1) ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] The shortest pulse length
On Fri, Mar 02, 2007 at 12:51:31AM -0800, seph 004 wrote: Thanks for the reply. I mentioned in my response to David's message that I'm purposefully setting the duc frequency to 0 to transmit at baseband. Is using .tune to do this better than the set_freq method even if I don't want duc to do anything to the signal? Regards Lance The good thing about tune is that it works the same way with all daughterboards. If you're using Basic Tx or LF Tx boards, the end result will be the same. tune will do all the work using the DUC. Eric ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] The shortest pulse length
On 3/1/07, seph 004 [EMAIL PROTECTED] wrote: This is what I did: def build_graph (): nchan = 1 interp = 512 duc0 = 0 duc1 = 0 fs = 250e3#2nd sample rate between usb and dac max_dev = 32e3 #1st sample rate divided by 4 (1st = 2nd sample rate) gain = 16e3 k = 2 * math.pi * max_dev / fs vec1 = Numeric.arange (0.624, 0.656, 0.128) vsource = gr.vector_source_f(vec1, False) fmmod = gr.frequency_modulator_fc (k) amp = gr.multiply_const_cc(gain) fg = gr.flow_graph () u = usrp.sink_c (0, interp, nchan) tx_subdev_spec = (1, 0) #usrp.pick_tx_subdevice(u) m = usrp.determine_tx_mux_value(u, tx_subdev_spec) u.set_mux(m) subdev = usrp.selected_subdev(u, tx_subdev_spec) subdev.set_enable(True) sample_rate = u.dac_freq () / interp u.set_tx_freq (0, duc0) u.set_tx_freq (1, duc1) Are you trying to use one daughter boards(nchen=1)? Why did you set duc0 = 0? that means your frequency will not be set at all. You do not need to do set_tx_freq() twice if you are using one daughter board. you only need : u.set_tx_freq (0, duc0) where duc0 is some frequency. Also, if you are using the basic daughterboards, you need to make sure that you have the output connector connect to TXA not TXB (according to your tx_subdev_spec) Hope this helped. David ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] The shortest pulse length
On Thu, Mar 01, 2007 at 12:15:36PM -0500, David Scaperoth wrote: On 3/1/07, seph 004 [EMAIL PROTECTED] wrote: This is what I did: def build_graph (): nchan = 1 interp = 512 duc0 = 0 duc1 = 0 fs = 250e3#2nd sample rate between usb and dac max_dev = 32e3 #1st sample rate divided by 4 (1st = 2nd sample rate) gain = 16e3 k = 2 * math.pi * max_dev / fs vec1 = Numeric.arange (0.624, 0.656, 0.128) vsource = gr.vector_source_f(vec1, False) fmmod = gr.frequency_modulator_fc (k) amp = gr.multiply_const_cc(gain) fg = gr.flow_graph () u = usrp.sink_c (0, interp, nchan) tx_subdev_spec = (1, 0) #usrp.pick_tx_subdevice(u) m = usrp.determine_tx_mux_value(u, tx_subdev_spec) u.set_mux(m) subdev = usrp.selected_subdev(u, tx_subdev_spec) subdev.set_enable(True) sample_rate = u.dac_freq () / interp u.set_tx_freq (0, duc0) u.set_tx_freq (1, duc1) Are you trying to use one daughter boards(nchen=1)? Why did you set duc0 = 0? that means your frequency will not be set at all. You do not need to do set_tx_freq() twice if you are using one daughter board. you only need : u.set_tx_freq (0, duc0) where duc0 is some frequency. Also, if you are using the basic daughterboards, you need to make sure that you have the output connector connect to TXA not TXB (according to your tx_subdev_spec) Hope this helped. David Lance, you really want to be using tune, not set_tx_freq. tune knows about all the daughterboards and does the right thing to split the work between the digital upconverter and the RF front end (if any). Take a look at fm_tx4.py or fm_tx_2_daughterboards.py Eric ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] The shortest pulse length
Well, I have implemented a bit of a strange setup which seems to be working somewhat now. I'm not really trying to view only the first few samples, I'm currently trying to track where I might of made a mistake with trying to generate a defined pulse with a specific length. My aim is to generate a very narrow band chirp to transmit on a little ultrasonic tranducer. I figured out which numerical values to the gr.modulation block produce which frequencies. Using this, I made a vector of the exact number of samples I want with the values to produce the frequencies I want. In my case 39-41 kHz. For some reason these low frequencies still make it through the transformer on the basic TX db, so I'm using them. Initially I was just generating a sine wave, and trying to use gr.head to limit the number of samples, but I've since switched to this approach I figured that if I wanted to produce a wave form lasting 10 msecs, then I would need at least 2500 samples. I got this number from the DAC rate of 128M and the highest interpolation factor of 512. When I test with the scope set to auto store, I spot the waveform, but it is only 1 msec long. So either I've lost a lot of samples somewhere, or my scaling is wrong. I pretty much abandoned using gr.head, as it wasn't producing anything. At least now though I can see a waveform, though my scaling seems to have gone wrong somewhere. When you say you used a looback, do you mean you connected the TX db output and RX db input, and used the gr.oscope block to view your signals? Regards Lance - Original Message From: Lee Patton [EMAIL PROTECTED] To: seph 004 [EMAIL PROTECTED] Cc: discuss-gnuradio@gnu.org Sent: Tuesday, February 27, 2007 12:58:31 AM Subject: Re: [Discuss-gnuradio] The shortest pulse length On Mon, 2007-02-26 at 00:55 -0800, seph 004 wrote: I have a vector source producing a sine wave, and then I'm using gr.head to limit the number of samples sent. I'm sure you checked this, but are you trying to capture the first few samples of sin(x)? I so, sin(x) = x for small angles, and sin(0)=0. So, you won't see anything in the first few samples anyway. From your explanation, I should be ok with even a low number of samples. When I tested my setup, I couldn't catch anything on the scope. There is probably some problem in how I made the app. I saw something mentioned elsewhere in the discussion archives that the usrp dumps the first few samples it receives from the host before transmitting. Is this still something to take note of? I don't know whether or not the USRP dumps the first few samples. I don't think I've ever experienced it though. I can say that there is an unpredictable delay from the generation of the first sample in software until the time it actually reaches the output port. I haven't tried to do what you're doing -- i.e., capture the first few output samples on a scope. How is the scope triggered? (What I did was create a loopback whereby I transmit and receive by reading the bleedover on the daugherboard.) -Lee Sucker-punch spam with award-winning protection. Try the free Yahoo! Mail Beta. http://advision.webevents.yahoo.com/mailbeta/features_spam.html___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] The shortest pulse length
On Feb 28, 2007, at 4:29 AM, seph 004 wrote: Well, I have implemented a bit of a strange setup which seems to be working somewhat now. I'm not really trying to view only the first few samples, I'm currently trying to track where I might of made a mistake with trying to generate a defined pulse with a specific length. My aim is to generate a very narrow band chirp to transmit on a little ultrasonic tranducer. I figured out which numerical values to the gr.modulation block produce which frequencies. Using this, I made a vector of the exact number of samples I want with the values to produce the frequencies I want. In my case 39-41 kHz. For some reason these low frequencies still make it through the transformer on the basic TX db, so I'm using them. Initially I was just generating a sine wave, and trying to use gr.head to limit the number of samples, but I've since switched to this approach I figured that if I wanted to produce a wave form lasting 10 msecs, then I would need at least 2500 samples. I got this number from the DAC rate of 128M and the highest interpolation factor of 512. When I test with the scope set to auto store, I spot the waveform, but it is only 1 msec long. So either I've lost a lot of samples somewhere, or my scaling is wrong. How are you creating the flow graph? I pretty much abandoned using gr.head, as it wasn't producing anything. At least now though I can see a waveform, though my scaling seems to have gone wrong somewhere. When you say you used a looback, do you mean you connected the TX db output and RX db input, and used the gr.oscope block to view your signals? Regards Lance - Original Message From: Lee Patton [EMAIL PROTECTED] To: seph 004 [EMAIL PROTECTED] Cc: discuss-gnuradio@gnu.org Sent: Tuesday, February 27, 2007 12:58:31 AM Subject: Re: [Discuss-gnuradio] The shortest pulse length On Mon, 2007-02-26 at 00:55 -0800, seph 004 wrote: I have a vector source producing a sine wave, and then I'm using gr.head to limit the number of samples sent. I'm sure you checked this, but are you trying to capture the first few samples of sin(x)? I so, sin(x) = x for small angles, and sin(0)=0. So, you won't see anything in the first few samples anyway. From your explanation, I should be ok with even a low number of samples. When I tested my setup, I couldn't catch anything on the scope. There is probably some problem in how I made the app. I saw something mentioned elsewhere in the discussion archives that the usrp dumps the first few samples it receives from the host before transmitting. Is this still something to take note of? I don't know whether or not the USRP dumps the first few samples. I don't think I've ever experienced it though. I can say that there is an unpredictable delay from the generation of the first sample in software until the time it actually reaches the output port. I haven't tried to do what you're doing -- i.e., capture the first few output samples on a scope. How is the scope triggered? (What I did was create a loopback whereby I transmit and receive by reading the bleedover on the daugherboard.) -Lee Now that's room service! Choose from over 150,000 hotels in 45,000 destinations on Yahoo! Travel to find your fit. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] The shortest pulse length
This is what I did: def build_graph (): nchan = 1 interp = 512 duc0 = 0 duc1 = 0 fs = 250e3#2nd sample rate between usb and dac max_dev = 32e3 #1st sample rate divided by 4 (1st = 2nd sample rate) gain = 16e3 k = 2 * math.pi * max_dev / fs vec1 = Numeric.arange (0.624, 0.656, 0.128) vsource = gr.vector_source_f(vec1, False) fmmod = gr.frequency_modulator_fc (k) amp = gr.multiply_const_cc(gain) fg = gr.flow_graph () u = usrp.sink_c (0, interp, nchan) tx_subdev_spec = (1, 0) #usrp.pick_tx_subdevice(u) m = usrp.determine_tx_mux_value(u, tx_subdev_spec) u.set_mux(m) subdev = usrp.selected_subdev(u, tx_subdev_spec) subdev.set_enable(True) sample_rate = u.dac_freq () / interp u.set_tx_freq (0, duc0) u.set_tx_freq (1, duc1) fg.connect (vsource, fmmod, amp, u) return fg I modified a version of siggen_min2.py into the above. Regards Lance - Original Message From: David Scaperoth [EMAIL PROTECTED] To: seph 004 [EMAIL PROTECTED] Cc: Lee Patton [EMAIL PROTECTED]; discuss-gnuradio@gnu.org Sent: Thursday, March 1, 2007 5:59:22 AM Subject: Re: [Discuss-gnuradio] The shortest pulse length On Feb 28, 2007, at 4:29 AM, seph 004 wrote: Well, I have implemented a bit of a strange setup which seems to be working somewhat now. I'm not really trying to view only the first few samples, I'm currently trying to track where I might of made a mistake with trying to generate a defined pulse with a specific length. My aim is to generate a very narrow band chirp to transmit on a little ultrasonic tranducer. I figured out which numerical values to the gr.modulation block produce which frequencies. Using this, I made a vector of the exact number of samples I want with the values to produce the frequencies I want. In my case 39-41 kHz. For some reason these low frequencies still make it through the transformer on the basic TX db, so I'm using them. Initially I was just generating a sine wave, and trying to use gr.head to limit the number of samples, but I've since switched to this approach I figured that if I wanted to produce a wave form lasting 10 msecs, then I would need at least 2500 samples. I got this number from the DAC rate of 128M and the highest interpolation factor of 512. When I test with the scope set to auto store, I spot the waveform, but it is only 1 msec long. So either I've lost a lot of samples somewhere, or my scaling is wrong. How are you creating the flow graph? I pretty much abandoned using gr.head, as it wasn't producing anything. At least now though I can see a waveform, though my scaling seems to have gone wrong somewhere. When you say you used a looback, do you mean you connected the TX db output and RX db input, and used the gr.oscope block to view your signals? Regards Lance - Original Message From: Lee Patton [EMAIL PROTECTED] To: seph 004 [EMAIL PROTECTED] Cc: discuss-gnuradio@gnu.org Sent: Tuesday, February 27, 2007 12:58:31 AM Subject: Re: [Discuss-gnuradio] The shortest pulse length On Mon, 2007-02-26 at 00:55 -0800, seph 004 wrote: I have a vector source producing a sine wave, and then I'm using gr.head to limit the number of samples sent. I'm sure you checked this, but are you trying to capture the first few samples of sin(x)? I so, sin(x) = x for small angles, and sin(0)=0. So, you won't see anything in the first few samples anyway. From your explanation, I should be ok with even a low number of samples. When I tested my setup, I couldn't catch anything on the scope. There is probably some problem in how I made the app. I saw something mentioned elsewhere in the discussion archives that the usrp dumps the first few samples it receives from the host before transmitting. Is this still something to take note of? I don't know whether or not the USRP dumps the first few samples. I don't think I've ever experienced it though. I can say that there is an unpredictable delay from the generation of the first sample in software until the time it actually reaches the output port. I haven't tried to do what you're doing -- i.e., capture the first few output samples on a scope. How is the scope triggered? (What I did was create a loopback whereby I transmit and receive by reading the bleedover on the daugherboard.) -Lee Now that's room service! Choose from over 150,000 hotels in 45,000 destinations on Yahoo! Travel to find your fit.___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio Want to start your own business? Learn how on Yahoo! Small Business. http://smallbusiness.yahoo.com/r
Re: [Discuss-gnuradio] The shortest pulse length
Hi Thanks very much for your explaination. I wasn't so sure what was happening with my setup. I have a vector source producing a sine wave, and then I'm using gr.head to limit the number of samples sent. From your explanation, I should be ok with even a low number of samples. When I tested my setup, I couldn't catch anything on the scope. There is probably some problem in how I made the app. I saw something mentioned elsewhere in the discussion archives that the usrp dumps the first few samples it receives from the host before transmitting. Is this still something to take note of? Regards Lance - Original Message From: Lee Patton [EMAIL PROTECTED] To: seph 004 [EMAIL PROTECTED] Cc: discuss-gnuradio@gnu.org Sent: Friday, February 23, 2007 6:07:45 PM Subject: Re: [Discuss-gnuradio] The shortest pulse length The shortest pulse duration which you can transmit is going to be limited by: a) the sampling rate of the converters b) the USB interface c) the bandwidth of IF/RF components I don't know your exact setup. So, let me provide an example of what I'm doing: I transmit and receive in an always-on fashion using a single USRP in 4 Byte/sample mode (2 for real, 2 for complex) Therefore, for each sample that must be transmitted and received, 8 bytes will traverse the USB (4 for Tx, 4 for Rx). The USRP is limited to 32 MB/s across the USB. Therefore, I can only handle signals 4 MHz wide. Because the USRP does complex sampling, 4 MHz becomes the maximum sampling rate I can use to generate my signal at baseband. (This signal will be interpolated to 128 MHz on the USRP.) Because the fastest I can generate samples is 4 MHz, the smallest interval between samples is 1/4e6 = 250 ns. That is (theoretically) the shortest pulse width. Now, anytime you signal using one sample you will suffer more system distortion than if you used, say, two. This is because the converters will act as a really wide low-pass filter. However, with that said, I am able to do it. I believe the minimum interpolation factor is 16. Therefore, in a transmit-only mode, I believe the minimum pulse width would be 1/8MHz = 125 ns. I haven't had coffee yet to day. So, caveat emptor on these calculations, but I hope they help. -Lee On Fri, 2007-02-23 at 06:08 -0800, seph 004 wrote: Hi Does anyone know what the shortest duration pulse is which the USRP can transmit? I've tried to test it by using gr.head to limit the number of samples to produce a short waveform, but I can't catch anything appearing at the output. Is there a simple test I could do to check? Regards Lance __ TV dinner still cooling? Check out Tonight's Picks on Yahoo! TV. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio Don't pick lemons. See all the new 2007 cars at Yahoo! Autos. http://autos.yahoo.com/new_cars.html ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] The shortest pulse length
On Mon, 2007-02-26 at 00:55 -0800, seph 004 wrote: I have a vector source producing a sine wave, and then I'm using gr.head to limit the number of samples sent. I'm sure you checked this, but are you trying to capture the first few samples of sin(x)? I so, sin(x) = x for small angles, and sin(0)=0. So, you won't see anything in the first few samples anyway. From your explanation, I should be ok with even a low number of samples. When I tested my setup, I couldn't catch anything on the scope. There is probably some problem in how I made the app. I saw something mentioned elsewhere in the discussion archives that the usrp dumps the first few samples it receives from the host before transmitting. Is this still something to take note of? I don't know whether or not the USRP dumps the first few samples. I don't think I've ever experienced it though. I can say that there is an unpredictable delay from the generation of the first sample in software until the time it actually reaches the output port. I haven't tried to do what you're doing -- i.e., capture the first few output samples on a scope. How is the scope triggered? (What I did was create a loopback whereby I transmit and receive by reading the bleedover on the daugherboard.) -Lee ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] The shortest pulse length
The shortest pulse duration which you can transmit is going to be limited by: a) the sampling rate of the converters b) the USB interface c) the bandwidth of IF/RF components I don't know your exact setup. So, let me provide an example of what I'm doing: I transmit and receive in an always-on fashion using a single USRP in 4 Byte/sample mode (2 for real, 2 for complex) Therefore, for each sample that must be transmitted and received, 8 bytes will traverse the USB (4 for Tx, 4 for Rx). The USRP is limited to 32 MB/s across the USB. Therefore, I can only handle signals 4 MHz wide. Because the USRP does complex sampling, 4 MHz becomes the maximum sampling rate I can use to generate my signal at baseband. (This signal will be interpolated to 128 MHz on the USRP.) Because the fastest I can generate samples is 4 MHz, the smallest interval between samples is 1/4e6 = 250 ns. That is (theoretically) the shortest pulse width. Now, anytime you signal using one sample you will suffer more system distortion than if you used, say, two. This is because the converters will act as a really wide low-pass filter. However, with that said, I am able to do it. I believe the minimum interpolation factor is 16. Therefore, in a transmit-only mode, I believe the minimum pulse width would be 1/8MHz = 125 ns. I haven't had coffee yet to day. So, caveat emptor on these calculations, but I hope they help. -Lee On Fri, 2007-02-23 at 06:08 -0800, seph 004 wrote: Hi Does anyone know what the shortest duration pulse is which the USRP can transmit? I've tried to test it by using gr.head to limit the number of samples to produce a short waveform, but I can't catch anything appearing at the output. Is there a simple test I could do to check? Regards Lance __ TV dinner still cooling? Check out Tonight's Picks on Yahoo! TV. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
