The C31XR-JK (Tribander) has been re-designed, optimized & Improved from the very popular Force 12 Tribander of all times for contesters and Dx’ers.
3 Elements on 20M / 4 Elements on 15M / 6 Elements on 10M / 30 Foot
Here are the important changes/features from the classic design ….
1. The Boom has been shortened by a foot to make it a 30Ft boom yagi
2. The feed point for 20M, 15M & 10M are connected using a transmission line, the same way as the JK-MidTri & JK-BigTri.
3. The mast mount position is right at the center of the antenna at 180″ with a gap of 25″ on either side for a total gap of 50″, which enables unhindered mounting on ring-rotors or side-mounting on towers.
4. The total number of elements on 10M has been reduced by 1 (one) element while optimizing gain and swr.
5. The overall gain and swr on all bands is consistent & provides excellent performance. (click here)
Price : US$1,895.00 **
Approx wt. = 110 lbs
Wind Area = 12.4 Sq. Ft
Max Wind Speed = 100 Mph
Max Turning Radius = 24 Ft
Feedpoint = Direct 50-Ohm
Peak Gain is shown over a dipole in Freespace
Dipole in Freespace = 2.14dBi
FREESPACE PLOTS – Single Antenna
| 10M | 15M | 20M | |
| Number Elements | 6 | 4 | 3 |
| Active Boom Length | 24 ft | 24.5 ft | 26.5 ft |
| Peak Gain* | 8+ dBd/10+ dbi | 7.5 dBd/ 9.5+ dbi | 6 dBd/ 8.2+ dbi |
| Peak F/B | 20+ dB | 15 dB | 18 dB |
| Peak F/R | 20+ dB | 15 dB | 18 dB |
| 2:1 SWR Bandwidth | 850 KHz | Less than 1.6:1 across the band | Less than 1.5:1 across the band |
| 1.5:1 SWR Bandwidth | 650 KHz | 450 KHz | 350 KHz |
| Max Element Length | 18 ft | 24.25 ft | 36.5 ft |
C31XR-JK : NEC4 – Freespace Gain, SWR & F/B values
| Freq | R | X | SWR | Gain | Azimuth Angle | F/B | F/R |
| 14.000 | 55.38 | -23.00 | 1.561 | 8.22 | 0 | 16.86 | 16.86 |
| 14.025 | 53.35 | -20.02 | 1.478 | 8.23 | 0 | 17.34 | 17.34 |
| 14.050 | 51.44 | -17.17 | 1.402 | 8.24 | 0 | 17.75 | 17.75 |
| 14.075 | 49.63 | -14.45 | 1.335 | 8.25 | 0 | 18.07 | 18.07 |
| 14.100 | 47.92 | -11.84 | 1.278 | 8.26 | 0 | 18.29 | 18.29 |
| 14.125 | 46.28 | -9.33 | 1.232 | 8.27 | 0 | 18.40 | 18.40 |
| 14.150 | 44.73 | -6.91 | 1.202 | 8.28 | 0 | 18.40 | 18.40 |
| 14.175 | 43.24 | -4.58 | 1.192 | 8.29 | 0 | 18.29 | 18.29 |
| 14.200 | 41.81 | -2.33 | 1.204 | 8.30 | 0 | 18.08 | 18.08 |
| 14.225 | 40.45 | -0.15 | 1.236 | 8.31 | 0 | 17.81 | 17.81 |
| 14.250 | 39.13 | 1.97 | 1.283 | 8.32 | 0 | 17.47 | 17.47 |
| 14.275 | 37.87 | 4.03 | 1.340 | 8.33 | 0 | 17.09 | 17.09 |
| 14.300 | 36.65 | 6.04 | 1.406 | 8.35 | 0 | 16.69 | 16.69 |
| 14.325 | 35.48 | 8.00 | 1.479 | 8.36 | 0 | 16.26 | 16.26 |
| 14.350 | 34.35 | 9.91 | 1.558 | 8.37 | 0 | 15.83 | 15.83 |
| Freq | R | X | SWR | Gain | Azimuth Angle | F/B | F/R |
| 21.000 | 52.94 | -25.35 | 1.634 | 9.50 | 0 | 15.66 | 15.66 |
| 21.025 | 54.09 | -19.77 | 1.471 | 9.53 | 0 | 15.62 | 15.62 |
| 21.050 | 55.30 | -14.68 | 1.344 | 9.55 | 0 | 15.58 | 15.58 |
| 21.075 | 56.53 | -10.09 | 1.253 | 9.58 | 0 | 15.54 | 15.54 |
| 21.100 | 57.77 | -6.01 | 1.200 | 9.60 | 0 | 15.49 | 15.49 |
| 21.125 | 58.96 | -2.46 | 1.186 | 9.62 | 0 | 15.44 | 15.44 |
| 21.150 | 60.06 | 0.55 | 1.202 | 9.65 | 0 | 15.40 | 15.40 |
| 21.175 | 61.00 | 3.02 | 1.229 | 9.67 | 0 | 15.36 | 15.36 |
| 21.200 | 61.68 | 4.96 | 1.256 | 9.69 | 0 | 15.31 | 15.31 |
| 21.225 | 62.01 | 6.38 | 1.276 | 9.71 | 0 | 15.26 | 15.26 |
| 21.250 | 61.87 | 7.35 | 1.285 | 9.73 | 0 | 15.21 | 15.21 |
| 21.275 | 61.16 | 7.96 | 1.280 | 9.75 | 0 | 15.14 | 15.14 |
| 21.300 | 59.77 | 8.35 | 1.264 | 9.77 | 0 | 15.05 | 15.05 |
| 21.325 | 57.65 | 8.70 | 1.240 | 9.79 | 0 | 14.94 | 14.94 |
| 21.350 | 54.79 | 9.20 | 1.219 | 9.81 | 0 | 14.79 | 14.79 |
| 21.375 | 51.27 | 10.05 | 1.221 | 9.83 | 0 | 14.59 | 14.59 |
| 21.400 | 47.21 | 11.44 | 1.273 | 9.85 | 0 | 14.34 | 14.34 |
| 21.425 | 42.78 | 13.48 | 1.390 | 9.87 | 0 | 14.03 | 14.03 |
| 21.450 | 38.20 | 16.22 | 1.576 | 9.89 | 0 | 13.64 | 13.64 |
| Freq | R | X | SWR | Gain | Azimuth Angle | F/B | F/R |
| 28.000 | 44.58 | -5.84 | 1.184 | 10.01 | 0 | 16.08 | 16.08 |
| 28.050 | 46.90 | -3.48 | 1.101 | 10.05 | 0 | 16.50 | 16.50 |
| 28.100 | 49.15 | -1.60 | 1.037 | 10.09 | 0 | 16.98 | 16.98 |
| 28.150 | 51.21 | -0.22 | 1.025 | 10.13 | 0 | 17.52 | 17.52 |
| 28.200 | 52.95 | 0.70 | 1.061 | 10.17 | 0 | 18.17 | 18.17 |
| 28.250 | 54.22 | 1.24 | 1.088 | 10.23 | 0 | 18.95 | 18.95 |
| 28.300 | 54.93 | 1.56 | 1.104 | 10.28 | 0 | 19.88 | 19.88 |
| 28.350 | 55.07 | 1.86 | 1.108 | 10.33 | 0 | 21.01 | 21.01 |
| 28.400 | 54.69 | 2.31 | 1.105 | 10.38 | 0 | 22.31 | 22.31 |
| 28.450 | 53.97 | 3.05 | 1.101 | 10.42 | 0 | 23.64 | 23.64 |
| 28.500 | 53.13 | 4.12 | 1.106 | 10.44 | 0 | 24.51 | 24.51 |
| 28.550 | 52.44 | 5.40 | 1.123 | 10.46 | 0 | 24.22 | 24.22 |
| 28.600 | 52.11 | 6.56 | 1.145 | 10.46 | 0 | 22.73 | 22.73 |
| 28.650 | 52.19 | 7.01 | 1.155 | 10.43 | 0 | 20.76 | 20.76 |
| 28.700 | 52.17 | 5.88 | 1.130 | 10.37 | 0 | 18.86 | 18.86 |
| 28.750 | 50.46 | 2.44 | 1.051 | 10.28 | 0 | 17.25 | 17.25 |
| 28.800 | 44.21 | -2.10 | 1.140 | 10.12 | 0 | 15.96 | 15.96 |
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