Hey guys, I have put together a noise figure meter application that uses a USRP as the sensing device. It started off as a way to measure the NF of the USRP itself. I have a calibrated noise source from an HP 8970B Noise Figure Meter. To test the NF of the USRP, I connect the head to the USRP input. My GNURadio flowgraph maximizes the USRP gain and measures a moving average of the received power while I switch the noise source on and off. The difference in the received power level, in addition to the ENR table from the noise source, can then be used to calculate the NF of the USRP itself using the y-factor method.
Once you have the NF for the USRP at many frequencies (I test every 50 MHz from 50 MHz - 6000 MHz), you can modify the same procedure to test the NF of a Device Under Test (DUT) which is connected between the noise source and the (now calibrated) USRP. You can use the USRP cal table we generated in the previous step to derive the NF of the DUT corrected for the NF of the USRP. In short, this all works incredibly well and garners very repeatable results. One complication is that you will see wild NF at certain frequencies due to local interference like LTE and WIFI. I've also compared the results to that which the HP device measures and they're very comparable. ... Except below ~ 1GHz. And here's the issue - I am seeing higher NF for DUTs below about 1GHz and particularly worse below 500 MHz. I was hoping someone at Ettus might be able to shed some light on why this might be. Curiously, the USRPs NF doesn't seem to be too bad, just the DUT. I'll note that I am nominally using a B200 for these tests, but I also tried an E312 just in case the filter banks might help out somehow. I didn't see a difference - they both had the same problem. I have used several DUTs for this test, including LNA boards we have designed ourselves and a Mini-Circuits ZX60-P103LN+ ( https://www.minicircuits.com/pdfs/ZX60-P103LN+.pdf). Both seem to exhibit higher NF when measured with a USRP below 1 GHz. When testing them on the HP NF meter, the NF is as expected all the way down to 50 MHz. I have attached the B200 cal data for your enjoyment as well as the B200-measured ZX60 NF and the HP-measured ZX60. The HP NF meter only goes up to 1600 MHz, which is why that data file stops there. I was surprised to see the B200 seemed to have a better NF than the E312, which averaged 8 dB NF, by the way. -- Very Respectfully, Dan CaJacob
Frequency,Noise ON,Noise OFF,NF 50.000, -136.472, -143.862, 6.570 100.000, -134.111, -142.368, 5.486 150.000, -133.334, -141.574, 5.508 200.000, -133.053, -142.054, 4.626 250.000, -133.068, -140.887, 6.011 300.000, -133.071, -142.151, 4.540 350.000, -132.990, -142.326, 4.250 400.000, -133.367, -142.289, 4.724 450.000, -133.049, -142.387, 4.252 500.000, -133.099, -142.421, 4.272 550.000, -133.312, -142.324, 4.625 600.000, -132.888, -141.866, 4.666 650.000, -133.159, -142.217, 4.577 700.000, -133.280, -142.570, 4.314 750.000, -132.448, -134.620, 14.941 800.000, -133.432, -142.585, 4.474 850.000, -133.411, -142.818, 4.186 900.000, -133.437, -142.720, 4.330 950.000, -133.865, -142.982, 4.519 1000.000, -133.771, -143.113, 4.265 1050.000, -134.097, -143.049, 4.709 1100.000, -134.481, -143.463, 4.674 1150.000, -134.487, -143.448, 4.699 1200.000, -134.837, -143.470, 5.076 1250.000, -135.162, -143.911, 4.942 1300.000, -135.202, -143.826, 5.087 1350.000, -135.499, -144.026, 5.200 1400.000, -135.723, -144.292, 5.151 1450.000, -135.752, -144.191, 5.303 1500.000, -135.799, -143.933, 5.660 1550.000, -135.983, -144.386, 5.345 1600.000, -135.936, -144.217, 5.487 1650.000, -136.055, -144.351, 5.470 1700.000, -136.269, -144.440, 5.616 1750.000, -136.258, -144.428, 5.618 1800.000, -136.686, -144.804, 5.680 1850.000, -136.977, -144.825, 6.001 1900.000, -136.969, -145.039, 5.736 1950.000, -137.084, -142.683, 8.870 2000.000, -137.789, -145.349, 6.347 2050.000, -137.800, -145.279, 6.450 2100.000, -138.521, -145.820, 6.672 2150.000, -138.037, -143.822, 8.624 2200.000, -138.324, -146.292, 5.869 2250.000, -138.322, -146.289, 5.873 2300.000, -138.999, -146.444, 6.505 2350.000, -138.739, -146.595, 6.012 2400.000, -138.524, -146.335, 6.069 2450.000, -138.959, -146.570, 6.312 2500.000, -138.681, -146.484, 6.084 2550.000, -138.529, -146.399, 6.007 2600.000, -138.784, -146.533, 6.155 2650.000, -138.807, -146.355, 6.402 2700.000, -139.190, -146.716, 6.431 2750.000, -139.572, -146.993, 6.561 2800.000, -140.187, -147.132, 7.153 2850.000, -140.921, -147.560, 7.543 2900.000, -141.454, -147.877, 7.824 2950.000, -142.067, -147.822, 8.714 3000.000, -142.869, -148.560, 8.805 3050.000, -143.345, -148.564, 9.468 3100.000, -143.877, -148.922, 9.722 3150.000, -144.308, -149.143, 10.035 3200.000, -144.770, -149.219, 10.627 3250.000, -145.015, -149.377, 10.766 3300.000, -145.155, -149.496, 10.804 3350.000, -145.516, -149.574, 11.263 3400.000, -145.565, -149.566, 11.362 3450.000, -145.478, -149.699, 11.005 3500.000, -145.751, -149.696, 11.460 3550.000, -145.823, -149.834, 11.355 3600.000, -145.556, -149.799, 10.980 3650.000, -145.769, -149.845, 11.254 3700.000, -145.826, -149.907, 11.250 3750.000, -145.665, -149.842, 11.096 3800.000, -145.920, -149.925, 11.382 3850.000, -145.945, -149.898, 11.473 3900.000, -145.954, -149.811, 11.638 3950.000, -146.205, -149.768, 12.154 4000.000, -142.078, -148.109, 8.415 4050.000, -142.259, -148.089, 8.691 4100.000, -142.582, -148.353, 8.777 4150.000, -142.371, -147.603, 9.535 4200.000, -142.700, -148.328, 8.984 4250.000, -142.921, -148.407, 9.188 4300.000, -142.828, -148.396, 9.080 4350.000, -142.804, -148.437, 8.996 4400.000, -142.935, -148.476, 9.129 4450.000, -142.795, -148.379, 9.076 4500.000, -142.581, -148.215, 9.013 4550.000, -142.719, -148.392, 8.965 4600.000, -142.543, -147.929, 9.369 4650.000, -142.501, -148.406, 8.663 4700.000, -142.443, -147.870, 9.323 4750.000, -142.612, -148.207, 9.097 4800.000, -142.693, -148.309, 9.074 4850.000, -142.814, -148.299, 9.260 4900.000, -143.003, -148.525, 9.214 4950.000, -143.382, -148.690, 9.521 5000.000, -143.497, -148.881, 9.419 5050.000, -143.566, -148.836, 9.591 5100.000, -144.008, -148.991, 10.014 5150.000, -143.955, -149.001, 9.931 5200.000, -143.905, -149.010, 9.857 5250.000, -144.259, -149.030, 10.358 5300.000, -144.054, -148.719, 10.527 5350.000, -143.939, -148.768, 10.291 5400.000, -144.203, -148.839, 10.591 5450.000, -144.178, -148.838, 10.563 5500.000, -144.006, -148.776, 10.407 5550.000, -144.221, -148.880, 10.583 5600.000, -144.400, -148.834, 10.939 5650.000, -144.579, -149.136, 10.759 5700.000, -144.744, -149.136, 11.025 5750.000, -145.241, -149.302, 11.567 5800.000, -145.401, -149.305, 11.836 5850.000, -145.632, -149.414, 12.054 5900.000, -146.083, -149.589, 12.550 5950.000, -146.281, -149.792, 12.551 6000.000, -146.480, -149.948, 12.639
Frequency,Insertion Gain,Noise Figure 50000000.000, 25.055, 1.411 100000000.000, 24.831, 0.875 150000000.000, 24.584, 0.549 200000000.000, 24.031, 0.400 250000000.000, 23.358, 0.328 300000000.000, 22.783, 0.262 350000000.000, 22.137, 0.248 400000000.000, 21.427, 0.263 450000000.000, 20.675, 0.355 500000000.000, 20.211, 0.417 550000000.000, 19.583, 0.487 600000000.000, 18.907, 0.606 650000000.000, 18.536, 0.634 700000000.000, 17.867, 0.694 750000000.000, 17.347, 3.477 800000000.000, 17.029, 0.799 850000000.000, 16.554, 0.849 900000000.000, 16.098, 0.922 950000000.000, 15.577, 0.908 1000000000.000, 15.415, 1.006 1050000000.000, 15.013, 0.957 1100000000.000, 14.590, 0.958 1150000000.000, 14.738, 0.950 1200000000.000, 14.199, 0.959 1250000000.000, 13.906, 0.963 1300000000.000, 13.109, 1.002 1350000000.000, 13.048, 0.934 1400000000.000, 12.752, 1.022 1450000000.000, 12.395, 1.336 1500000000.000, 12.142, 1.434 1550000000.000, 12.343, 1.067 1600000000.000, 11.880, 0.984
Frequency,Insertion Gain,Noise Figure 50000000.000, 21.113, 3.952 100000000.000, 19.361, 6.057 150000000.000, 18.648, 5.670 200000000.000, 18.171, 5.441 250000000.000, 18.462, 4.709 300000000.000, 18.106, 4.448 350000000.000, 17.916, 3.861 400000000.000, 18.319, 3.297 450000000.000, 17.709, 3.302 500000000.000, 17.568, 2.581 550000000.000, 17.714, 2.607 600000000.000, 16.995, 2.459 650000000.000, 16.992, 1.987 700000000.000, 16.942, 2.114 750000000.000, 19.130, 1.969 800000000.000, 16.420, 1.700 850000000.000, 16.114, 1.545 900000000.000, 15.432, 1.363 950000000.000, 15.836, 1.494 1000000000.000, 15.000, 1.141 1050000000.000, 14.693, 1.245 1100000000.000, 15.217, 1.139 1150000000.000, 13.782, 1.064 1200000000.000, 13.909, 1.180 1250000000.000, 14.361, 0.981 1300000000.000, 12.611, 1.081 1350000000.000, 13.187, 1.089 1400000000.000, 13.231, 1.108 1450000000.000, 11.575, 1.319 1500000000.000, 12.290, 1.375 1550000000.000, 12.020, 1.108 1600000000.000, 11.428, 0.979 1650000000.000, 11.932, 1.056 1700000000.000, 10.745, 0.977 1750000000.000, 11.256, 0.976 1800000000.000, 10.993, 1.176 1850000000.000, 9.642, 0.885 1900000000.000, 11.114, 1.063 1950000000.000, 10.068, 1.826 2000000000.000, 8.921, 1.010 2050000000.000, 10.603, 1.328 2100000000.000, 9.211, 0.971 2150000000.000, 8.428, 1.504 2200000000.000, 8.294, 1.221 2250000000.000, 10.335, 1.383 2300000000.000, 7.813, 1.130 2350000000.000, 7.656, 1.500 2400000000.000, 9.737, 1.457 2450000000.000, 7.400, 1.546 2500000000.000, 7.363, 1.660 2550000000.000, 8.602, 1.523 2600000000.000, 7.229, 1.531 2650000000.000, 5.328, 12.506 2700000000.000, 7.110, 1.661 2750000000.000, 7.337, 1.606 2800000000.000, 7.238, 1.998 2850000000.000, 5.788, 1.922 2900000000.000, 7.079, 1.955 2950000000.000, 6.856, 2.294 3000000000.000, 5.148, 1.981
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