Ah ok, I was (wrongly) assuming Khalid just leaves the TX port virtually open.
Greetings, Marcus On 01/06/2015 08:21 PM, Marcus D. Leech wrote: > On 01/06/2015 02:17 PM, Marcus Müller wrote: >>> >Is the input impedance of your scope 1Mohm or 50 ohms? >>> Yes, it is 1 Mohm, >> >> Well, in that case, your power consideration is not really correct; >> the LFTX is designed for 50 Ohm load impedance; so, for meaningful >> measurements, you'd have to measure the voltage over 50 Ohm. >> I'm not really sure how much current the opamp on the LFTX is >> designed to source, but I think adding a 50 Ohm load would reduce the >> current through the negative feedback resistors R4/R7 (and in turn >> reduce the bias over R33-R3/R35-R6) , which might change your >> measurements significantly. >> >> Greetings, >> Marcus > The AD8047 is designed for a max of 50mA drive current. If you do the > math, that's plenty. > > I believe that Khalid was terminating in 50Ohms resistive, so with a > 1Mohm impedance across that, the scope input impedance will hardly > make any > difference at all--it should "see" the voltage developed across that > 50Ohms, without noticeably changing it. > > >> >> On 01/06/2015 08:09 PM, khalid.el-darymli wrote: >>> Yes, it is 1 Mohm, and my probe is set to 1X. >>> >>> Khalid >>> >>> >>> On Tue, Jan 6, 2015 at 3:33 PM, Nick Foster <bistrom...@gmail.com >>> <mailto:bistrom...@gmail.com>> wrote: >>> >>> Is the input impedance of your scope 1Mohm or 50 ohms? You sure >>> you have the voltage multiplier (1x/10x) set correctly? >>> >>> On Tue, Jan 6, 2015 at 11:01 AM, khalid.el-darymli >>> <khalid.el-dary...@mun.ca <mailto:khalid.el-dary...@mun.ca>> wrote: >>> >>> >> Trying setting a gain in your sink block of, let's say, >>> 20dB, with a magnitude of 0.9. What power output do you >>> get? How are you measuring power? >>> >>> This gives me 23.2 mV (peak to peak). This is the reading I >>> get from a scope connected to a T. For the input ends of the >>> T, one end is connected to a 50-ohm terminator and the other >>> end is connected to the output from LFTX. This gives a power >>> of: 30+10 log_10[{23.2e-03/[2*sqrt(2)]}^2/50]= *-28.711* dBm. >>> >>> >> What is your flow-graph actually doing? Have you tried >>> both connectors on the LFTX? >>> >>> Simple, a signal source (Sine) block directly connected to a >>> USRP Sink block. >>> Yes, both connectors on the LFTX daughterboard give the same >>> voltage reading. >>> >>> Thanks, >>> Khalid >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> On Tue, Jan 6, 2015 at 2:34 PM, Marcus D. Leech >>> <mle...@ripnet.com <mailto:mle...@ripnet.com>> wrote: >>> >>>> >>>> >> Output power is determined largely by baseband >>>> signal magnitude in that case. >>>> Yes, I understand. And I noticed that for baseband >>>> signal with an amplitude *> 1, * the pass-band signal >>>> gets clipped off. So I assume that an amplitude of 1 >>>> for the baseband signal should deliver the maximum >>>> output power (for the pass-band signal). >>>> >>>> My question was, what is the maximum power one can get >>>> for the pass-band signal output from LFTX? In your >>>> earlier reply, you said it is around +7dBm, am I >>>> getting this right? In my case, for a baseband >>>> amplitude of around 1, I am only getting *-28.13dBm*, >>>> much less than what you said, I am not sure,*why?* >>>> >>>> Thanks, >>>> Khalid >>>> >>> For a magnitude of ~1, you should see maximum amplitude >>> signals coming out of it. >>> >>> You could try setting gain, but on any platforms with >>> VGAs in the DAC, there's only about 6dB of gain range >>> settable. Trying setting a gain in your >>> sink block of, let's say, 20dB, with a magnitude of >>> 0.9. What power output do you get? How are you >>> measuring power? What is your flow-graph >>> actually doing? Have you tried both connectors on the >>> LFTX? >>> >>> >>> >>>> >>>> On Tue, Jan 6, 2015 at 1:56 PM, Marcus D. Leech >>>> <mle...@ripnet.com <mailto:mle...@ripnet.com>> wrote: >>>> >>>>> Thanks Marcus for your reply. >>>>> >>>>> >> Probably somewhere in the neighborhood of +7dBm, >>>>> maybe a little more. >>>>> >>>>> >> The LF/BASIC series have *no* gain in either >>>>> path, so you're just looked >>>>> at buffered ADC ouput. >>>>> >>>>> So, ~ *+7dBm* is the max output power I supposed >>>>> to get from the LFTX daughterboard? How do I get that? >>>>> >>>>> Since I am only getting -28.13 dBm, does that mean >>>>> I have some issue with my LFTX daughterboard? >>>>> >>>>> >>>>> Khalid >>>>> >>>>> >>>> Output power is determined largely by baseband >>>> signal magnitude in that case. >>>> >>>> >>>> >>>> >>>> >>>>> >>>>> >>>>> >>>>> >>>>> Message: 2 >>>>> Date: Tue, 6 Jan 2015 10:13:45 -0330 >>>>> From: "khalid.el-darymli" >>>>> <khalid.el-dary...@mun.ca >>>>> <mailto:khalid.el-dary...@mun.ca>> >>>>> To: "Discuss-gnuradio@gnu.org >>>>> <mailto:Discuss-gnuradio@gnu.org>" >>>>> <discuss-gnuradio@gnu.org >>>>> <mailto:discuss-gnuradio@gnu.org>> >>>>> Subject: [Discuss-gnuradio] Max Output Power from >>>>> the LFTX >>>>> daughterboard >>>>> Message-ID: >>>>> <CACdmG=zCHATiwrtv=wBVLwG0_ >>>>> 5GQr0y=wksequrcajrtuv5...@mail.gmail.com >>>>> <mailto:wksequrcajrtuv5...@mail.gmail.com>> >>>>> Content-Type: text/plain; charset="utf-8" >>>>> >>>>> Hi, >>>>> >>>>> What is the maximum output power from the LFTX >>>>> daughterboard when used with >>>>> the USRP N200? >>>>> >>>>> According to this datasheet [1], the N200 with the >>>>> WBX daughterbaord >>>>> provide an output power of 15 dBm. However, when >>>>> using the LFTX >>>>> daughterboard, I am getting a much less output power. >>>>> [1] >>>>> >>>>> http://www.ettus.com/content/files/07495_Ettus_N200-210_DS_Flyer_HR.pdf >>>>> >>>>> In GNU Radio with the USRP N200, we use a sinusoid >>>>> with a frequency of 150 >>>>> kHz and an amplitude of 0.98, fed into the LFTX >>>>> daughterboard for a center >>>>> frequency of 5 MHz. When the output of LFTX is >>>>> plugged into a scope >>>>> terminated with a 50-ohm terminator, the scope >>>>> reads 24.8 mV >>>>> (peak-to-peak). This is around -28.13 dBm. >>>>> >>>>> Is this the max power one can get out of the LFTX >>>>> daughterboard? >>>>> >>>>> >>>>> Thanks. >>>>> >>>>> Best regards, >>>>> Khalid >>>>> -------------- next part -------------- >>>>> An HTML attachment was scrubbed... >>>>> URL: >>>>> >>>>> <http://lists.gnu.org/archive/html/discuss-gnuradio/attachments/20150106/37846ff4/attachment.html> >>>>> >>>>> ------------------------------ >>>>> >>>>> Message: 3 >>>>> Date: Tue, 06 Jan 2015 08:48:08 -0500 >>>>> From: "Marcus D. Leech" <mle...@ripnet.com >>>>> <mailto:mle...@ripnet.com>> >>>>> To: discuss-gnuradio@gnu.org >>>>> <mailto:discuss-gnuradio@gnu.org> >>>>> Subject: Re: [Discuss-gnuradio] Max Output Power >>>>> from the LFTX >>>>> daughterboard >>>>> Message-ID: <54abe798.5060...@ripnet.com >>>>> <mailto:54abe798.5060...@ripnet.com>> >>>>> Content-Type: text/plain; charset=UTF-8; format=flowed >>>>> >>>>> On 01/06/2015 08:43 AM, khalid.el-darymli wrote: >>>>> > Hi, >>>>> > >>>>> > What is the maximum output power from the LFTX >>>>> daughterboard when used >>>>> > with the USRP N200? >>>>> > >>>>> > According to this datasheet [1], the N200 with >>>>> the WBX daughterbaord >>>>> > provide an output power of 15 dBm. However, when >>>>> using the LFTX >>>>> > daughterboard, I am getting a much less output >>>>> power. >>>>> > [1] >>>>> > >>>>> >>>>> http://www.ettus.com/content/files/07495_Ettus_N200-210_DS_Flyer_HR.pdf >>>>> > >>>>> > In GNU Radio with the USRP N200, we use a >>>>> sinusoid with a frequency of >>>>> > 150 kHz and an amplitude of 0.98, fed into the >>>>> LFTX daughterboard for >>>>> > a center frequency of 5 MHz. When the output of >>>>> LFTX is plugged into a >>>>> > scope terminated with a 50-ohm terminator, the >>>>> scope reads 24.8 mV >>>>> > (peak-to-peak). This is around -28.13 dBm. >>>>> > >>>>> > Is this the max power one can get out of the >>>>> LFTX daughterboard? >>>>> > >>>>> > >>>>> > Thanks. >>>>> > >>>>> > Best regards, >>>>> > Khalid >>>>> Probably somewhere in the neighborhood of +7dBm, >>>>> maybe a little more. >>>>> >>>>> The LF/BASIC series have *no* gain in either path, >>>>> so you're just looked >>>>> at buffered ADC ouput. >>>>> >>>>> >>>>> >>>>> -- >>>>> Marcus Leech >>>>> Principal Investigator >>>>> Shirleys Bay Radio Astronomy Consortium >>>>> http://www.sbrac.org >>>> >>>> >>>> -- >>>> Marcus Leech >>>> Principal Investigator >>>> Shirleys Bay Radio Astronomy Consortium >>>> http://www.sbrac.org >>>> >>>> >>>> >>>> >>> >>> >>> -- >>> Marcus Leech >>> Principal Investigator >>> Shirleys Bay Radio Astronomy Consortium >>> http://www.sbrac.org >>> >>> >>> >>> >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >>> >>> >>> >>> >>> >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> Discuss-gnuradio@gnu.org >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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