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 > >
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