> >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 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
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