Michael - Hm, I don't understand what you are attempting to measure. Measuring the input IP3 (IIP3) for a transmitter doesn't mean anything. All that matters is output IP3 (OIP3). The e-mail you linked to is Marcus explaining how to measure the IIP3 through the receive-only port of a daughterboard, using the same daughterboard as a signal source. You are attempting to measure the IIP3 of a transmitter only - whatever data you collect won't tell you anything meaningful.
David - Gain levels are approximate, and it is also possible that at the upper amplitudes the ADCs are clipping anyway. Cheers, Ben On Wed, Sep 12, 2012 at 7:56 PM, David Bengtson <david.bengt...@gmail.com>wrote: > Let me preface this by saying I mostly lurk on this list, and haven't > touched a USRP of any variety, so I'm unfamiliar with their gain lineup. > However, looking at this data, a couple of things come to mind. > > 1-You're sweeping the gain by 35 dB, and the amplitude is moving by 28 dB, > which seems to indicate to me that something strange is going on with the > levels. > > 2-I graphed the levels of the tones, and they aren't moving in amplitude > until the gain setting is 15 or so, which seems unusal to me. What does the > spectrum analyzer display look like when you are doing this? Do you see > visible tones at deltaF? What about at other frequencies? Are you using a > real SA or the USRP? > > 3-The other thing to look at and worry about are IP5/IP7 tones, which can > really be a problem when you're approaching P1dB on the output power. I'm > suspicious that at higher gain settings, you're starting to see these tones > show up. > > Here's the google spreadsheet I imported your data into. > > > https://docs.google.com/spreadsheet/ccc?key=0AmZNNcsCPNTZdFRyWi1Ed2VHR29DRC1hSFY5V1AzV0E > > > Dave > On Mon, Sep 10, 2012 at 10:32 AM, Michael Hill <moth...@gmail.com> wrote: > >> Apologies that copy paste formatting was attrocious..! Data attached in >> file. >> >> P.S. earlier I meant to say f1 = 4MHz and f2 = 5 MHz >> In the attached data >> >> m1 = 2*f1-f2 >> m2 = f1 >> m3 = f2 >> m4 = 2*f2-f1 >> >> thx! >> >> >> On Mon, Sep 10, 2012 at 10:56 PM, Michael Hill <moth...@gmail.com> wrote: >> >>> >>> Can anyone provide any insight into why i'm getting the results I am? >>> The aim of this test was to measure the OIP3 during transmit, then >>> determine the IIP3. >>> >>> *Conditions* >>> I conducted two-tone tests using f1 = 4 MHz and f3 = 5 MHz. >>> The LO was set to 2400, 2450, 2500, 4900, 5400 and 6000 MHz (I'm using >>> the XCVR2450 with the USRP N210) >>> The Amplitude variable has been set to 0.25, and the gain has been >>> stepped from 0 to 35dB. >>> >>> The two tone test was essentially setup as the same in this link but >>> with the the output measured by an oscilloscope, thus i'm sure i've done it >>> right.. >>> http://lists.gnu.org/archive/html/discuss-gnuradio/2011-10/msg00433.html >>> >>> >>> *Measurements* >>> I've measured the power amplitudes, also the gain has been calculated at >>> each step (since the gain request may not actually get the specific gain). >>> Measurements have been taken with an agilent spec amp at 300Hz. >>> >>> I've then calculated the OIP3 and subtracted the actual gain to get the >>> IIP3. >>> >>> *Results* >>> However, my data is a bit odd... An example has been provided in the >>> table below. It seems that my intermodulation products are not increasing >>> at 3dB for each 1dB.. >>> What does this imply? >>> >>> Examples of my transmit IIP3 results are attached, these seem somewhat >>> in the jagged ball park of the receiver results below for the WBX. >>> http://code.ettus.com/redmine/ettus/documents/16 >>> Not an apple to apple comparison I know.. but I don't have much to go >>> on.. >>> am I missing something basic (I am still.. in my opinion.. new) >>> >>> (Note: units below are MHz for frequencies, and dB for gain, dBm for >>> the output power.) >>> >>> Carrier m1 m2 m3 m4 2400 3 4 5 6 2400 MHz 2403 >>> 2404 2405 2406 Gain 0 -50.27 -11.88 -11.58 >>> -49.31 1 -49.79 -11.05 -10.79 -48.74 2 -49.37 -10.37 -10.09 -49.06 >>> 3 -48.77 -9.62 -9.36 -47.62 4 -48.89 -8.93 -8.67 -47.66 5 -48.16 >>> -8.08 -7.79 -47.26 6 -48.5 -7.43 -7.16 -46.71 7 -47.9 -6.63 -6.36 >>> -48.1 8 -47.52 -5.98 -5.7 -46.06 9 -46.65 -5.24 -4.98 -46 10 >>> -48.13 -4.58 -4.36 -46.07 11 -46.95 -3.84 -3.63 -47.07 12 -47.6 >>> -3.23 -3.02 -45.6 13 -47.14 -2.51 -2.32 -46.78 14 -47.74 -1.81 >>> -1.62 -48.15 15 -47.98 -0.98 -0.78 -45.74 16 -47.06 -0.31 -0.14 >>> -46.42 17 -47.58 0.48 0.67 -47.57 18 -46.64 1.24 1.39 -47.44 19 >>> -46.15 2 2.2 -46.19 20 -43.16 2.87 3.04 -44.33 21 -40.62 3.71 3.86 >>> -42.54 22 -39.47 4.48 4.61 -39.99 23 -36.41 5.24 5.36 -37.01 24 >>> -35.01 6.03 6.16 -35.63 25 -32.85 6.81 6.94 -33.63 26 -31.27 7.72 >>> 7.87 -31.36 27 -29.14 8.62 8.7 -30.24 28 -27.78 9.59 9.7 -27.9 29 >>> -26.18 10.68 10.82 -26.36 30 -24.77 12.03 12.14 -25.26 31 -25.29 >>> 12.04 12.15 -25.62 32 -18.65 13.93 14.03 -19.96 33 -10.29 15.26 >>> 15.33 -10.31 34 -9.91 15.25 15.33 -10.09 35 -4.42 16.22 16.3 -4.33 >>> >> >> >> _______________________________________________ >> 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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