Coil size, inductance, resistance, and Q
Chuck Agosta - Clark University
The following chart shows the calculated inductance and resistance of small coils in the size range that we often use with our TDO circuits. In addition the frequency of oscillation is calculated assuming 1 pF of capacitance and 1 uH of additional inductance, the absolute minimum one might expect from a real circuit. In most real circuits the parasitic inductance and capacitance will be greater and the resonant frequency lower. See the TDO tests chart for typical real values. The Q is also calculated. It is based on the resistance and does not account for radiation, so it sets an upper limit. The inductance is a good starting point if the actual parasitic values are known. See the detailed way to do that calculation here (coming soon).
In this table the three wire diameters are in mm and correspond to #56, #50, and #45 wire respectively. Inductance is in uH, resistance in Ω, and frequency in MHz.
wire | dia | turns | Induc | Resis | Q | MHz | wire | dia | turns | Induc | Resis | Q | MHz | wire | dia | turns | Induc | Resis | Q | MHz |
0.0125 | 1.5 | 1 | 4.704 | 1.68 | 37.1 | 2107 | 0.02504 | 1.5 | 1 | 4.02 | 0.81 | 70.2 | 2246 | 0.0447 | 1.5 | 1 | 3.493 | 0.46 | 113.5 | 2374 |
0.0125 | 1.5 | 2 | 17.221 | 2.69 | 47.5 | 1179 | 0.02504 | 1.5 | 2 | 14.535 | 1.24 | 93.7 | 1277 | 0.0447 | 1.5 | 2 | 12.523 | 0.7 | 152.9 | 1369 |
0.0125 | 1.5 | 3 | 36.606 | 3.56 | 53 | 821 | 0.02504 | 1.5 | 3 | 30.301 | 1.59 | 107.4 | 900 | 0.0447 | 1.5 | 3 | 25.821 | 0.9 | 175.7 | 972 |
0.0125 | 1.5 | 4 | 61.673 | 4.4 | 56 | 636 | 0.02504 | 1.5 | 4 | 50.698 | 1.91 | 117 | 700 | 0.0447 | 1.5 | 4 | 42.689 | 1.07 | 191.6 | 761 |
0.0125 | 1.5 | 5 | 91.657 | 5.21 | 57.8 | 523 | 0.02504 | 1.5 | 5 | 74.894 | 2.2 | 123.8 | 578 | 0.0447 | 1.5 | 5 | 62.529 | 1.22 | 203.2 | 631 |
0.0125 | 1.5 | 6 | 127.705 | 6 | 59.4 | 444 | 0.02504 | 1.5 | 6 | 102.826 | 2.47 | 129.1 | 494 | 0.0447 | 1.5 | 6 | 85.223 | 1.36 | 212.8 | 542 |
0.0125 | 1.5 | 7 | 167.045 | 6.78 | 60.1 | 388 | 0.02504 | 1.5 | 7 | 133.756 | 2.74 | 133.1 | 434 | 0.0447 | 1.5 | 7 | 109.964 | 1.5 | 219.9 | 478 |
0.0125 | 1.5 | 8 | 212.191 | 7.54 | 60.9 | 345 | 0.02504 | 1.5 | 8 | 167.79 | 2.99 | 136.4 | 387 | 0.0447 | 1.5 | 8 | 136.618 | 1.63 | 225.5 | 429 |
0.0125 | 1.5 | 9 | 259.725 | 8.31 | 61.2 | 312 | 0.02504 | 1.5 | 9 | 204.281 | 3.25 | 138.9 | 351 | 0.0447 | 1.5 | 9 | 165.098 | 1.76 | 230.2 | 391 |
0.0125 | 1.5 | 10 | 311.007 | 9.07 | 61.4 | 285 | 0.02504 | 1.5 | 10 | 243.422 | 3.49 | 141 | 322 | 0.0447 | 1.5 | 10 | 195.482 | 1.88 | 234.3 | 359 |
0.0125 | 1.0 | 1 | 2.895 | 1.22 | 38.1 | 2550 | 0.02504 | 1.0 | 1 | 2.448 | 0.59 | 70.2 | 2710 | 0.0447 | 1.0 | 1 | 2.108 | 0.34 | 111.2 | 2855 |
0.0125 | 1.0 | 2 | 10.51 | 1.96 | 50.1 | 1483 | 0.02504 | 1.0 | 2 | 8.755 | 0.93 | 95.2 | 1611 | 0.0447 | 1.0 | 2 | 7.452 | 0.53 | 151.8 | 1731 |
0.0125 | 1.0 | 3 | 22.214 | 2.58 | 56.4 | 1045 | 0.02504 | 1.0 | 3 | 18.086 | 1.2 | 109.3 | 1152 | 0.0447 | 1.0 | 3 | 15.18 | 0.69 | 174.1 | 1251 |
0.0125 | 1.0 | 4 | 37.215 | 3.17 | 60 | 814 | 0.02504 | 1.0 | 4 | 30.029 | 1.43 | 119 | 904 | 0.0447 | 1.0 | 4 | 24.836 | 0.82 | 189 | 990 |
0.0125 | 1.0 | 5 | 55.002 | 3.74 | 62.1 | 673 | 0.02504 | 1.0 | 5 | 44.03 | 1.65 | 125.7 | 750 | 0.0447 | 1.0 | 5 | 36.022 | 0.94 | 199.5 | 827 |
0.0125 | 1.0 | 6 | 76.344 | 4.29 | 64 | 572 | 0.02504 | 1.0 | 6 | 60.056 | 1.86 | 130.9 | 644 | 0.0447 | 1.0 | 6 | 48.68 | 1.05 | 207.9 | 714 |
0.0125 | 1.0 | 7 | 99.39 | 4.83 | 64.9 | 502 | 0.02504 | 1.0 | 7 | 77.615 | 2.05 | 134.8 | 568 | 0.0447 | 1.0 | 7 | 62.276 | 1.16 | 213.8 | 633 |
0.0125 | 1.0 | 8 | 125.82 | 5.36 | 65.9 | 447 | 0.02504 | 1.0 | 8 | 96.793 | 2.24 | 137.9 | 509 | 0.0447 | 1.0 | 8 | 76.758 | 1.26 | 218.2 | 571 |
0.0125 | 1.0 | 9 | 153.357 | 5.89 | 66.2 | 405 | 0.02504 | 1.0 | 9 | 117.158 | 2.43 | 140.3 | 463 | 0.0447 | 1.0 | 9 | 92.056 | 1.36 | 221.7 | 522 |
0.0125 | 1.0 | 10 | 182.917 | 6.42 | 66.5 | 371 | 0.02504 | 1.0 | 10 | 138.86 | 2.61 | 142.2 | 426 | 0.0447 | 1.0 | 10 | 108.261 | 1.46 | 224.7 | 481 |
0.0125 | 0.7 | 1 | 1.88 | 0.91 | 38.3 | 2966 | 0.02504 | 0.7 | 1 | 1.575 | 0.45 | 68.9 | 3136 | 0.0447 | 0.7 | 1 | 1.345 | 0.26 | 106.9 | 3287 |
0.0125 | 0.7 | 2 | 6.769 | 1.49 | 51.7 | 1806 | 0.02504 | 0.7 | 2 | 5.568 | 0.72 | 95 | 1964 | 0.0447 | 0.7 | 2 | 4.685 | 0.42 | 148.2 | 2111 |
0.0125 | 0.7 | 3 | 14.22 | 1.96 | 58.8 | 1290 | 0.02504 | 0.7 | 3 | 11.39 | 0.94 | 109.3 | 1430 | 0.0447 | 0.7 | 3 | 9.419 | 0.54 | 169.7 | 1559 |
0.0125 | 0.7 | 4 | 23.682 | 2.4 | 62.8 | 1013 | 0.02504 | 0.7 | 4 | 18.756 | 1.12 | 118.9 | 1132 | 0.0447 | 0.7 | 4 | 15.237 | 0.65 | 183.5 | 1249 |
0.0125 | 0.7 | 5 | 34.793 | 2.82 | 65.2 | 841 | 0.02504 | 0.7 | 5 | 27.278 | 1.29 | 125.3 | 946 | 0.0447 | 0.7 | 5 | 21.866 | 0.75 | 192.6 | 1052 |
0.0125 | 0.7 | 6 | 48.099 | 3.22 | 67.3 | 718 | 0.02504 | 0.7 | 6 | 36.946 | 1.46 | 130.2 | 817 | 0.0447 | 0.7 | 6 | 29.285 | 0.84 | 199.6 | 915 |
0.0125 | 0.7 | 7 | 62.3 | 3.62 | 68.3 | 633 | 0.02504 | 0.7 | 7 | 47.414 | 1.61 | 133.7 | 723 | 0.0447 | 0.7 | 7 | 37.124 | 0.93 | 204.2 | 815 |
0.0125 | 0.7 | 8 | 78.577 | 4.01 | 69.4 | 564 | 0.02504 | 0.7 | 8 | 58.758 | 1.76 | 136.5 | 651 | 0.0447 | 0.7 | 8 | 45.384 | 1.02 | 207.4 | 739 |
0.0125 | 0.7 | 9 | 95.34 | 4.4 | 69.8 | 513 | 0.02504 | 0.7 | 9 | 70.677 | 1.91 | 138.5 | 594 | 0.0447 | 0.7 | 9 | 54.001 | 1.1 | 209.6 | 679 |
0.0125 | 0.7 | 10 | 113.238 | 4.78 | 70.1 | 471 | 0.02504 | 0.7 | 10 | 83.295 | 2.05 | 140.1 | 548 | 0.0447 | 0.7 | 10 | 63.076 | 1.18 | 211.6 | 629 |
0.0125 | 0.5 | 1 | 1.246 | 0.69 | 37.9 | 3358 | 0.02504 | 0.5 | 1 | 1.036 | 0.35 | 66.4 | 3528 | 0.0447 | 0.5 | 1 | 0.878 | 0.2 | 100.7 | 3673 |
0.0125 | 0.5 | 2 | 4.445 | 1.15 | 52.4 | 2157 | 0.02504 | 0.5 | 2 | 3.611 | 0.57 | 93.3 | 2344 | 0.0447 | 0.5 | 2 | 3.005 | 0.33 | 141.9 | 2515 |
0.0125 | 0.5 | 3 | 9.276 | 1.52 | 60.2 | 1570 | 0.02504 | 0.5 | 3 | 7.305 | 0.74 | 107.6 | 1746 | 0.0447 | 0.5 | 3 | 5.95 | 0.44 | 162.5 | 1909 |
0.0125 | 0.5 | 4 | 15.346 | 1.86 | 64.6 | 1245 | 0.02504 | 0.5 | 4 | 11.918 | 0.9 | 116.9 | 1400 | 0.0447 | 0.5 | 4 | 9.504 | 0.53 | 174.9 | 1553 |
0.0125 | 0.5 | 5 | 22.395 | 2.18 | 67.2 | 1041 | 0.02504 | 0.5 | 5 | 17.172 | 1.04 | 122.8 | 1181 | 0.0447 | 0.5 | 5 | 13.477 | 0.61 | 182.5 | 1323 |
0.0125 | 0.5 | 6 | 30.818 | 2.48 | 69.6 | 892 | 0.02504 | 0.5 | 6 | 23.075 | 1.17 | 127.3 | 1026 | 0.0447 | 0.5 | 6 | 17.873 | 0.69 | 188.2 | 1159 |
0.0125 | 0.5 | 7 | 39.686 | 2.79 | 70.6 | 789 | 0.02504 | 0.5 | 7 | 29.379 | 1.29 | 130.3 | 913 | 0.0447 | 0.5 | 7 | 22.434 | 0.77 | 191.4 | 1040 |
0.0125 | 0.5 | 8 | 49.846 | 3.08 | 71.8 | 706 | 0.02504 | 0.5 | 8 | 36.155 | 1.41 | 132.6 | 826 | 0.0447 | 0.5 | 8 | 27.192 | 0.84 | 193.3 | 948 |
0.0125 | 0.5 | 9 | 60.168 | 3.37 | 72.2 | 644 | 0.02504 | 0.5 | 9 | 43.188 | 1.53 | 134.1 | 757 | 0.0447 | 0.5 | 9 | 32.09 | 0.91 | 194.4 | 875 |
0.0125 | 0.5 | 10 | 71.123 | 3.66 | 72.4 | 593 | 0.02504 | 0.5 | 10 | 50.587 | 1.65 | 135.2 | 701 | 0.0447 | 0.5 | 10 | 37.227 | 0.97 | 195.4 | 814 |
0.0125 | 0.3 | 1 | 0.663 | 0.45 | 35.9 | 3903 | 0.02504 | 0.3 | 1 | 0.544 | 0.23 | 60.4 | 4050 | 0.0447 | 0.3 | 1 | 0.457 | 0.14 | 88.1 | 4170 |
0.0125 | 0.3 | 2 | 2.323 | 0.78 | 51.8 | 2761 | 0.02504 | 0.3 | 2 | 1.85 | 0.4 | 87.4 | 2981 | 0.0447 | 0.3 | 2 | 1.513 | 0.24 | 126.8 | 3175 |
0.0125 | 0.3 | 3 | 4.786 | 1.04 | 60.5 | 2092 | 0.02504 | 0.3 | 3 | 3.663 | 0.53 | 101.3 | 2331 | 0.0447 | 0.3 | 3 | 2.912 | 0.32 | 145.2 | 2545 |
0.0125 | 0.3 | 4 | 7.818 | 1.27 | 65.4 | 1695 | 0.02504 | 0.3 | 4 | 5.871 | 0.64 | 109.9 | 1920 | 0.0447 | 0.3 | 4 | 4.545 | 0.39 | 155.3 | 2137 |
0.0125 | 0.3 | 5 | 11.263 | 1.49 | 68.1 | 1437 | 0.02504 | 0.3 | 5 | 8.312 | 0.75 | 114.7 | 1649 | 0.0447 | 0.3 | 5 | 6.308 | 0.46 | 160.6 | 1862 |
0.0125 | 0.3 | 6 | 15.363 | 1.7 | 70.6 | 1244 | 0.02504 | 0.3 | 6 | 11.009 | 0.85 | 118.2 | 1452 | 0.0447 | 0.3 | 6 | 8.227 | 0.52 | 164.3 | 1657 |
0.0125 | 0.3 | 7 | 19.566 | 1.9 | 71.7 | 1110 | 0.02504 | 0.3 | 7 | 13.814 | 0.94 | 120.1 | 1308 | 0.0447 | 0.3 | 7 | 10.154 | 0.58 | 165.5 | 1507 |
0.0125 | 0.3 | 8 | 24.38 | 2.1 | 72.9 | 999 | 0.02504 | 0.3 | 8 | 16.793 | 1.04 | 121.6 | 1193 | 0.0447 | 0.3 | 8 | 12.145 | 0.64 | 165.9 | 1388 |
0.0125 | 0.3 | 9 | 29.142 | 2.29 | 73.2 | 917 | 0.02504 | 0.3 | 9 | 19.814 | 1.12 | 122.1 | 1103 | 0.0447 | 0.3 | 9 | 14.145 | 0.69 | 165.6 | 1293 |
0.0125 | 0.3 | 10 | 34.144 | 2.49 | 73.3 | 849 | 0.02504 | 0.3 | 10 | 22.971 | 1.21 | 122.6 | 1028 | 0.0447 | 0.3 | 10 | 16.245 | 0.75 | 165.4 | 1212 |
0.0125 | 0.2 | 1 | 0.399 | 0.32 | 33.3 | 4255 | 0.02504 | 0.2 | 1 | 0.325 | 0.17 | 54 | 4372 | 0.0447 | 0.2 | 1 | 0.272 | 0.1 | 76.1 | 4463 |
0.0125 | 0.2 | 2 | 1.375 | 0.57 | 49.5 | 3266 | 0.02504 | 0.2 | 2 | 1.078 | 0.3 | 79.6 | 3491 | 0.0447 | 0.2 | 2 | 0.872 | 0.18 | 110.5 | 3679 |
0.0125 | 0.2 | 3 | 2.794 | 0.77 | 58.7 | 2584 | 0.02504 | 0.2 | 3 | 2.088 | 0.41 | 92.6 | 2864 | 0.0447 | 0.2 | 3 | 1.63 | 0.25 | 126.2 | 3104 |
0.0125 | 0.2 | 4 | 4.507 | 0.95 | 63.7 | 2145 | 0.02504 | 0.2 | 4 | 3.29 | 0.5 | 100.4 | 2430 | 0.0447 | 0.2 | 4 | 2.491 | 0.31 | 134.6 | 2694 |
0.0125 | 0.2 | 5 | 6.408 | 1.12 | 66.4 | 1849 | 0.02504 | 0.2 | 5 | 4.578 | 0.59 | 104.2 | 2131 | 0.0447 | 0.2 | 5 | 3.392 | 0.37 | 138.2 | 2401 |
0.0125 | 0.2 | 6 | 8.664 | 1.28 | 69 | 1619 | 0.02504 | 0.2 | 6 | 5.984 | 0.67 | 106.9 | 1904 | 0.0447 | 0.2 | 6 | 4.365 | 0.42 | 140.7 | 2173 |
0.0125 | 0.2 | 7 | 10.912 | 1.43 | 69.8 | 1458 | 0.02504 | 0.2 | 7 | 7.409 | 0.75 | 108 | 1736 | 0.0447 | 0.2 | 7 | 5.314 | 0.48 | 140.7 | 2003 |
0.0125 | 0.2 | 8 | 13.492 | 1.58 | 71 | 1322 | 0.02504 | 0.2 | 8 | 8.913 | 0.82 | 108.8 | 1599 | 0.0447 | 0.2 | 8 | 6.296 | 0.52 | 140.6 | 1863 |
0.0125 | 0.2 | 9 | 15.973 | 1.72 | 71.1 | 1222 | 0.02504 | 0.2 | 9 | 10.407 | 0.9 | 108.7 | 1490 | 0.0447 | 0.2 | 9 | 7.259 | 0.57 | 139.5 | 1751 |
0.0125 | 0.2 | 10 | 18.559 | 1.87 | 71 | 1138 | 0.02504 | 0.2 | 10 | 11.967 | 0.97 | 108.7 | 1398 | 0.0447 | 0.2 | 10 | 8.281 | 0.62 | 139 | 1652 |