Re: [Discuss-gnuradio] Dynamic range of USRP2-XCVR2450
On 10/24/2010 04:27 PM, Jorge Miguel wrote: > I will have a look at the white papers from that manufacturers. > From your words, I imagine that the noise generated by the ADC will > set a limit in the noise floor at the input of the ADC, isn´t it? Yes. The total signal power arriving at the A/D (signal+noise) must exceed the effective noise floor of the A/D by enough margin to allow "demodulation" of your signal of interest. Where "demodulation" is very loosely defined. Each modulation technique has its own SNR requirements. I do radio astronomy, where there's no demodulation, per se. In fact, most of the time my "signals" are *below* the total noise floor of the receiving system. But I have the very great advantage of being able to maximize bandwidth and integration time in order to "see" those below-the-noise-floor signals. -- 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] Dynamic range of USRP2-XCVR2450
Hi Marcus, -10dBm corresponds to 100µW. With an input impedance of 100Ohms, since Pmax rms= (Vmax rms)^2 / R, --> Vmax rms= 0.1 volt So, if I am right the maximum theoretical voltage at the input of the ADC, if 0 dB gain is set in the transceiver (XCVR2450 in my case) and noise figure of all components were 0 dB, is 0.1 volt However the gain of the transceiver is set to increase this [0 - 0.1] volt range to [0 - 1] volt range at the input of the ADC. Is it right ? Regarding the value of the ADC SNR (72.4dB), why is it important if it doesn´t depend on the input range? (SNR= 6.02*N + 1.76) There is something I miss..grr ! Many thanks. Jorge. On 24 October 2010 19:57, Marcus D. Leech wrote: > On 10/24/2010 01:07 PM, Jorge Miguel wrote: > > Hello, > > > > I am trying to find out the minimum/maximun input power of the ADC > > LTC2284. > > I know that the maximum input voltage is 1 Volt, 0.707Vrms, but what > > is the input impedance? so that I can calculate the maximum input > > power as: > > > > minimum input power (SNR ADC) = Maximun input power > > ( [(0.707)/(2^14))^2]/Rin) + 72.4 dB = Maximun input power > > > > Am I right? > > > > Many thanks, > > Jorge > > > > > I believe that it's a 100ohm balanced input. > > But the daughtercards all take a 50-ohm input, and convert to a balanced > output just before the > A/D. > > With the exception of the Basic_RX and LFRX, the maximum input power for > any of the other > daughtercards is below -10dBm. > > The BASIC_RX and LFRX have a maximum input power of about +10dBm. > > > > > -- > 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] Dynamic range of USRP2-XCVR2450
On 10/24/2010 01:07 PM, Jorge Miguel wrote: > Hello, > > I am trying to find out the minimum/maximun input power of the ADC > LTC2284. > I know that the maximum input voltage is 1 Volt, 0.707Vrms, but what > is the input impedance? so that I can calculate the maximum input > power as: > > minimum input power (SNR ADC) = Maximun input power > ( [(0.707)/(2^14))^2]/Rin) + 72.4 dB = Maximun input power > > Am I right? > > Many thanks, > Jorge > > I believe that it's a 100ohm balanced input. But the daughtercards all take a 50-ohm input, and convert to a balanced output just before the A/D. With the exception of the Basic_RX and LFRX, the maximum input power for any of the other daughtercards is below -10dBm. The BASIC_RX and LFRX have a maximum input power of about +10dBm. -- 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] Dynamic range of USRP2-XCVR2450
Hello, I am trying to find out the minimum/maximun input power of the ADC LTC2284. I know that the maximum input voltage is 1 Volt, 0.707Vrms, but what is the input impedance? so that I can calculate the maximum input power as: minimum input power (SNR ADC) = Maximun input power ( [(0.707)/(2^14))^2]/Rin) + 72.4 dB = Maximun input power Am I right? Many thanks, Jorge On 19 October 2010 19:18, Marcus D. Leech wrote: > On 10/19/2010 12:21 PM, Jorge Miguel wrote: > > Hi Marcus! > > How do you get the 85 dB value? Is the Intermodulation distorsion of the > page 3 ADC datasheet? > > In the "features" list for the LTC2284: > > 72.4dB SNR, 88dB SFDR > > SFDR is "spur-free dynamic range". > > > > I am not an expecienced engineer (I am recent graduated) but I was thinking > about the maximun and minimum input powers to be linearly detected in the > USRP receiver. > > > > I thought the ADC as a good point to start with and then see what is going > on in the XCVR2450 transceiver > > At the ADC point, it is said that is has 2volts p-p dynamic range. This > value can give us the maximun power input at the ADC provided the input > impedance.(Good question. What is the input impedance? I cannot see it in > the ADC datasheet) > > > > P=(V^2)/R > > Is it right? In other post I can read:*"ADC's datasheet, we need 2Vp-p to > fully utilise its dynamic range. The input impedance of the ADC is around > 220ohms so this is equal to an input signal level of about 6dBm. If you go > above this you will get saturation."* > I do the calculations and it doesn't match!!! > > The LTC2284 can be configured for either 1VP-P or 2VP-P. I believe the > USRP2 uses 1VP-P configuration. > > Generally, with ADCs, you ascribe roughly 6dB of dynamic range per bit, > this is a 14-bit A/D. > > > > Before the ADC is the XCVR2450, with all RF components. Each one of then > has its Noise figure and some of them gain such us the power amplifier or > the Maxim. > > You said that *"The XCVR2450 does have gain control, but it is solely > under control of the host software"*. Besides the ones I mentioned, is > there any other place with gain? > > The MAX2829 has roughly 93dB of RX gain-control range--that's right on the > data sheet, and is "exposed" to the API inside Gnu Radio. > When you create a source, you can specify the gain (actually, you can > change it dynamically as well). > > > > > > Is it the correct way of calculating the dynamic range? > I really need help. > > Thanks, > Jorge. >> >> >> > The LTC2284 A/D is a 14-bit A/D. The maximum input voltage the way it's > configured is 0.707Vrms. Divide that by the > 2^14, and that's roughly your minimum input voltage. In general, though > you take a little bit off the top and add a little > bit onto the bottom of the range. > > > Google is your friend. I'd suggest looking up "ADC noise floor dynamic > range". Plenty of articles out there. > > > > -- > Marcus Leech > Principal Investigator > Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org > > ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Dynamic range of USRP2-XCVR2450
On 10/19/2010 12:21 PM, Jorge Miguel wrote: > Hi Marcus! > > How do you get the 85 dB value? Is the Intermodulation distorsion of > the page 3 ADC datasheet? In the "features" list for the LTC2284: 72.4dB SNR, 88dB SFDR SFDR is "spur-free dynamic range". > > I am not an expecienced engineer (I am recent graduated) but I was > thinking about the maximun and minimum input powers to be linearly > detected in the USRP receiver. > > I thought the ADC as a good point to start with and then see what is > going on in the XCVR2450 transceiver > > At the ADC point, it is said that is has 2volts p-p dynamic range. > This value can give us the maximun power input at the ADC provided the > input impedance.(Good question. What is the input impedance? I cannot > see it in the ADC datasheet) > > P=(V^2)/R > > Is it right? In other post I can read:/"ADC's datasheet, we need 2Vp-p > to fully utilise its dynamic range. The input impedance of the ADC is > around 220ohms so this is equal to an input signal level of about > 6dBm. If you go above this you will get saturation."/ > I do the calculations and it doesn't match!!! The LTC2284 can be configured for either 1VP-P or 2VP-P. I believe the USRP2 uses 1VP-P configuration. Generally, with ADCs, you ascribe roughly 6dB of dynamic range per bit, this is a 14-bit A/D. > > > Before the ADC is the XCVR2450, with all RF components. Each one of > then has its Noise figure and some of them gain such us the power > amplifier or the Maxim. > > You said that /"The XCVR2450 does have gain control, but it is solely > under control of the host software"/. Besides the ones I mentioned, > is there any other place with gain? > The MAX2829 has roughly 93dB of RX gain-control range--that's right on the data sheet, and is "exposed" to the API inside Gnu Radio. When you create a source, you can specify the gain (actually, you can change it dynamically as well). > Is it the correct way of calculating the dynamic range? > I really need help. > > Thanks, > Jorge. > > > The LTC2284 A/D is a 14-bit A/D. The maximum input voltage the way it's configured is 0.707Vrms. Divide that by the 2^14, and that's roughly your minimum input voltage. In general, though you take a little bit off the top and add a little bit onto the bottom of the range. Google is your friend. I'd suggest looking up "ADC noise floor dynamic range". Plenty of articles out there. -- 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
[Discuss-gnuradio] Dynamic range of USRP2-XCVR2450
Hi, I am trying to find out the dynamic range of the system USRP2-XCVR2450. Looking at the schematics it seems there isn't automatic gain control in the whole RF chain, Isn't it? Thus the dynamic range of the system would be the ADC dynamic range, which is 2 volts Am I right? Cheers, Jorge. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
