Here are NEC2 model results comparing a
helix with a vertical monopole. The helix is 12" diameter with 4 segments per turn. This passes segmentation checks in NEC2 at this frequency. This helix is resonant and does not require a loading coil. The monopole model uses a .625in OD copper pipe, but the diameter of a monopole doesn't change the gain.
Important results:
Radiation Resistance:
Helix = .23 ohms, Monopole - .1 ohms
Gain:
Helix = -11.73 dBi, Monopole - -15.09 dBi
Resonant Freq: 1.706 MHz.
Helix configuration: 4-sided square loop per turn, helix diameter=12"
Helix Turns: 115
Segment Check: Pass
Wire Size: #14
Height: 3 meters
Total Segments: 461
Ground Resistance: 10 ohms
Helix Coil Loss Resistance: 0
Ground: Perfect
Impedance at antenna base: 10.23 - J 0.1759 ohms
Radiation Resistance: .23 ohms
Far Field Gain: -11.14 dBi
Accuracy Check: Average Gain = 1.146 = 0.59 dB
Corrected Far Field Gain: -11.14 - 0.59 = -11.73 dBi
The model for a 3 meter base-loaded monopole gives these results:
Resonant Freq: 1.6 MHz.
Segment Check: Pass
Wire Size: 0.625 in. (1/2" copper pipe)
Height: 3 meters
Total Segments: 16
Ground Resistance: 10 ohms
Coil Loss Resistance: 0 (not possible, but chosen for comparison to helix above)
Ground: Perfect
Impedance at antenna base: 10.1 - J 0.02625 ohms
Radiation Resistance: .1 ohms
Far Field Gain: -15.09 dBi
Accuracy Check: Average Gain = 0.999 = 0 dB
Corrected Far Field Gain: -15.09 - 0 = -15.09 dBi
3.36 dBi gain advantage goes to helix, and in reality, the advantage may be even higher compared to a base-loaded monopole. The results for the monopole assumed zero coil loss to focus the comparison on a zero coil loss helix vs. monopole. An actual monopole antenna may have a coil loss of 5 to 15 ohms, so the gain advantage for the helix would be even higher. I don't know what the coil loss would be for the helix, but I think it would be very low.
The 12" diameter of the helix may not pass muster with the FCC. A smaller diameter helix with more turns is certainly workable. Unfortunately it can't be modeled accurately with NEC-2 due to minimum segment size restrictions.
EDITED Thu Apr 7, 2011 10:05pm PDT
It's designed for elevation, so some say the transmission line cable constitutes much of its radiation efficiency and is illegal. Same basic thing applies to EH antennas.
The model apparently doesn't consider what happens to the 1/2" pipe antenna if there is a loading coil of the type usually considered for use, whereas I assume the helix antenna includes coil inductance inherent in its structure.
So, what would the overall gain be if the base loading coil is used with the mnnopole? What if a similar base loading coil were used with a helix antenna ... i.e., it seems like it would raise the wire resistance so much it would lose more than it gains.
What happens when you add ground radials to each?
I don't have the software, can't run it on this machine, but maybe on my little netbook.
Here's the other thing I was looking for:
http://www.antennex.com/shack/Jun00/paperdavos.pdf
Notice how similar this thing looks to the squirrel cage monopole
Ken,
As stated, the model deliberately sets the helical coil loss resistance and the monopole base loading coil loss resistance to zero for an apples-to-apples comparison.
The loss resistance of the helix is unknown. I think it would be very low because it is a well spaced air-core coil. Likely a loading coil for a monopole will typically have significantly higher loss than the helix coil, so the gain advantage of the helix would be even higher.
I'm sure an extreme case could be conjured up where the helix coil loss would be high. Off hand, an extreme example would be a very small diameter helix wound with very fine wire.
I've modeled a similar antenna using NEC-2 a while ago (1`foot diameter, square loops, and 90 turns). At 1.6 MHz, the input impedance was .1823 - j 445 ohms. I tried adding turns to the helix to cancel out the capacitive input reactance, but I was not able to get resonance. Not being able to approach resonance by adding turns was an unphysical result. Since I was trying to test the NEC-2 simulation program, and not an actual antenna, I assumed perfect ground, and a rather thin wire diameter. Like PhilB, I also obtained no segmentation error message with my own simulation.
I like PhilB's results because they appear reasonable, but I am not yet sure that the NEC-2 simulation is robust for a one foot helix diameter. I've obtained what appear to me like more convincing results with much larger diameter and fewer turns.
I repeated PhilB's simulation of of a 115-turn vertical helical monopole over ground, 1-foot in diameter and 3 m high. I got a resonant frequency of 1.7386 MHz instead of 1.706 MHz. Using the Wheeler formula, the inductance of the helical coil is found to be 385.8 uH, giving a self-capacitance of the coil of 21.7 pF. The Medhurst self-capacitance of the coil is about 42 pF, which would give a resonant frequency of 1.25 Mhz. If there were only 90 turns, the resonant frequency would be 1.6 MHz.
Considering the large diameter of the helix, 21.7 pF would be too small a self-capacitance. NEC-2 predicts too high a number of turns for resonance of the helix. The higher the number of turns in the helix, the lower self-capacitance predicted by NEC-2 would be. According to Medhurst, the self capacitance is determined by the dimensions of the coil, and not the number of turns.
When you take into account that a variable diameter of a helical monopole horizontally grounded beyond the reverse harmonic of precoiled inductor, then you will see that the true capacitance can be judged as vertical coil in respect to the wheeler formula as Medhurst clearly demonstrates.
Such information could prove invaluable providing you don't turn it over.
I'm aware that's total gibberish, I just kind of wanted to join the discussion, but I can't understand a word your all saying.
Ermi,
Here is the input file I used for the helical antenna simulation. It was created and modeled using 4nec2 software (download is free).
GW 1 1 0 0 0 0 0 8 0.03204186
GW 2 1 0 0 8 0 6 13.2285 0.03204186
GW 3 1 0 6 13.2285 -6 0 13.457 0.03204186
GW 4 1 -6 0 13.457 0 -6 13.6855 0.03204186
GW 5 1 0 -6 13.6855 6 0 13.914 0.03204186
GW 6 1 6 0 13.914 0 6 14.1425 0.03204186
GW 7 1 0 6 14.1425 -6 0 14.371 0.03204186
GW 8 1 -6 0 14.371 0 -6 14.5995 0.03204186
GW 9 1 0 -6 14.5995 6 0 14.828 0.03204186
GW 10 1 6 0 14.828 0 6 15.0565 0.03204186
GW 11 1 0 6 15.0565 -6 0 15.285 0.03204186
GW 12 1 -6 0 15.285 0 -6 15.5135 0.03204186
GW 13 1 0 -6 15.5135 6 0 15.742 0.03204186
GW 14 1 6 0 15.742 0 6 15.9705 0.03204186
GW 15 1 0 6 15.9705 -6 0 16.199 0.03204186
GW 16 1 -6 0 16.199 0 -6 16.4275 0.03204186
GW 17 1 0 -6 16.4275 6 0 16.656 0.03204186
GW 18 1 6 0 16.656 0 6 16.8845 0.03204186
GW 19 1 0 6 16.8845 -6 0 17.113 0.03204186
GW 20 1 -6 0 17.113 0 -6 17.3415 0.03204186
GW 21 1 0 -6 17.3415 6 0 17.57 0.03204186
GW 22 1 6 0 17.57 0 6 17.7985 0.03204186
GW 23 1 0 6 17.7985 -6 0 18.027 0.03204186
GW 24 1 -6 0 18.027 0 -6 18.2555 0.03204186
GW 25 1 0 -6 18.2555 6 0 18.484 0.03204186
GW 26 1 6 0 18.484 0 6 18.7125 0.03204186
GW 27 1 0 6 18.7125 -6 0 18.941 0.03204186
GW 28 1 -6 0 18.941 0 -6 19.1695 0.03204186
GW 29 1 0 -6 19.1695 6 0 19.398 0.03204186
GW 30 1 6 0 19.398 0 6 19.6265 0.03204186
GW 31 1 0 6 19.6265 -6 0 19.855 0.03204186
GW 32 1 -6 0 19.855 0 -6 20.0835 0.03204186
GW 33 1 0 -6 20.0835 6 0 20.312 0.03204186
GW 34 1 6 0 20.312 0 6 20.5405 0.03204186
GW 35 1 0 6 20.5405 -6 0 20.769 0.03204186
GW 36 1 -6 0 20.769 0 -6 20.9975 0.03204186
GW 37 1 0 -6 20.9975 6 0 21.226 0.03204186
GW 38 1 6 0 21.226 0 6 21.4545 0.03204186
GW 39 1 0 6 21.4545 -6 0 21.683 0.03204186
GW 40 1 -6 0 21.683 0 -6 21.9115 0.03204186
GW 41 1 0 -6 21.9115 6 0 22.14 0.03204186
GW 42 1 6 0 22.14 0 6 22.3685 0.03204186
GW 43 1 0 6 22.3685 -6 0 22.597 0.03204186
GW 44 1 -6 0 22.597 0 -6 22.8255 0.03204186
GW 45 1 0 -6 22.8255 6 0 23.054 0.03204186
GW 46 1 6 0 23.054 0 6 23.2825 0.03204186
GW 47 1 0 6 23.2825 -6 0 23.511 0.03204186
GW 48 1 -6 0 23.511 0 -6 23.7395 0.03204186
GW 49 1 0 -6 23.7395 6 0 23.968 0.03204186
GW 50 1 6 0 23.968 0 6 24.1965 0.03204186
GW 51 1 0 6 24.1965 -6 0 24.4249961 0.03204186
GW 52 1 -6 0 24.4249961 0 -6 24.6535 0.03204186
GW 53 1 0 -6 24.6535 6 0 24.882 0.03204186
GW 54 1 6 0 24.882 0 6 25.1105 0.03204186
GW 55 1 0 6 25.1105 -6 0 25.339 0.03204186
GW 56 1 -6 0 25.339 0 -6 25.5675 0.03204186
GW 57 1 0 -6 25.5675 6 0 25.796 0.03204186
GW 58 1 6 0 25.796 0 6 26.0245 0.03204186
GW 59 1 0 6 26.0245 -6 0 26.253 0.03204186
GW 60 1 -6 0 26.253 0 -6 26.4815 0.03204186
GW 61 1 0 -6 26.4815 6 0 26.71 0.03204186
GW 62 1 6 0 26.71 0 6 26.9385 0.03204186
GW 63 1 0 6 26.9385 -6 0 27.167 0.03204186
GW 64 1 -6 0 27.167 0 -6 27.3955 0.03204186
GW 65 1 0 -6 27.3955 6 0 27.6239961 0.03204186
GW 66 1 6 0 27.6239961 0 6 27.8525 0.03204186
GW 67 1 0 6 27.8525 -6 0 28.081 0.03204186
GW 68 1 -6 0 28.081 0 -6 28.3095 0.03204186
GW 69 1 0 -6 28.3095 6 0 28.538 0.03204186
GW 70 1 6 0 28.538 0 6 28.7665 0.03204186
GW 71 1 0 6 28.7665 -6 0 28.995 0.03204186
GW 72 1 -6 0 28.995 0 -6 29.2235 0.03204186
GW 73 1 0 -6 29.2235 6 0 29.452 0.03204186
GW 74 1 6 0 29.452 0 6 29.6805 0.03204186
GW 75 1 0 6 29.6805 -6 0 29.909 0.03204186
GW 76 1 -6 0 29.909 0 -6 30.1375 0.03204186
GW 77 1 0 -6 30.1375 6 0 30.366 0.03204186
GW 78 1 6 0 30.366 0 6 30.5945 0.03204186
GW 79 1 0 6 30.5945 -6 0 30.8229961 0.03204186
GW 80 1 -6 0 30.8229961 0 -6 31.0515 0.03204186
GW 81 1 0 -6 31.0515 6 0 31.28 0.03204186
GW 82 1 6 0 31.28 0 6 31.5085 0.03204186
GW 83 1 0 6 31.5085 -6 0 31.737 0.03204186
GW 84 1 -6 0 31.737 0 -6 31.9655 0.03204186
GW 85 1 0 -6 31.9655 6 0 32.194 0.03204186
GW 86 1 6 0 32.194 0 6 32.4225 0.03204186
GW 87 1 0 6 32.4225 -6 0 32.651 0.03204186
GW 88 1 -6 0 32.651 0 -6 32.8795 0.03204186
GW 89 1 0 -6 32.8795 6 0 33.108 0.03204186
GW 90 1 6 0 33.108 0 6 33.3364961 0.03204186
GW 91 1 0 6 33.3364961 -6 0 33.565 0.03204186
GW 92 1 -6 0 33.565 0 -6 33.7935 0.03204186
GW 93 1 0 -6 33.7935 6 0 34.0219961 0.03204186
GW 94 1 6 0 34.0219961 0 6 34.2505 0.03204186
GW 95 1 0 6 34.2505 -6 0 34.479 0.03204186
GW 96 1 -6 0 34.479 0 -6 34.7075 0.03204186
GW 97 1 0 -6 34.7075 6 0 34.936 0.03204186
GW 98 1 6 0 34.936 0 6 35.1645 0.03204186
GW 99 1 0 6 35.1645 -6 0 35.393 0.03204186
GW 100 1 -6 0 35.393 0 -6 35.6215 0.03204186
GW 101 1 0 -6 35.6215 6 0 35.8499961 0.03204186
GW 102 1 6 0 35.8499961 0 6 36.0785 0.03204186
GW 103 1 0 6 36.0785 -6 0 36.307 0.03204186
GW 104 1 -6 0 36.307 0 -6 36.5354961 0.03204186
GW 105 1 0 -6 36.5354961 6 0 36.764 0.03204186
GW 106 1 6 0 36.764 0 6 36.9925 0.03204186
GW 107 1 0 6 36.9925 -6 0 37.221 0.03204186
GW 108 1 -6 0 37.221 0 -6 37.4495 0.03204186
GW 109 1 0 -6 37.4495 6 0 37.678 0.03204186
GW 110 1 6 0 37.678 0 6 37.9065 0.03204186
GW 111 1 0 6 37.9065 -6 0 38.135 0.03204186
GW 112 1 -6 0 38.135 0 -6 38.3635 0.03204186
GW 113 1 0 -6 38.3635 6 0 38.592 0.03204186
GW 114 1 6 0 38.592 0 6 38.8205 0.03204186
GW 115 1 0 6 38.8205 -6 0 39.0489961 0.03204186
GW 116 1 -6 0 39.0489961 0 -6 39.2775 0.03204186
GW 117 1 0 -6 39.2775 6 0 39.5059843 0.03204186
GW 118 1 6 0 39.5059843 0 6 39.7344882 0.03204186
GW 119 1 0 6 39.7344882 -6 0 39.9629921 0.03204186
GW 120 1 -6 0 39.9629921 0 -6 40.1914961 0.03204186
GW 121 1 0 -6 40.1914961 6 0 40.42 0.03204186
GW 122 1 6 0 40.42 0 6 40.6485039 0.03204186
GW 123 1 0 6 40.6485039 -6 0 40.8770079 0.03204186
GW 124 1 -6 0 40.8770079 0 -6 41.1055118 0.03204186
GW 125 1 0 -6 41.1055118 6 0 41.3340157 0.03204186
GW 126 1 6 0 41.3340157 0 6 41.5624803 0.03204186
GW 127 1 0 6 41.5624803 -6 0 41.7909843 0.03204186
GW 128 1 -6 0 41.7909843 0 -6 42.0194882 0.03204186
GW 129 1 0 -6 42.0194882 6 0 42.2479921 0.03204186
GW 130 1 6 0 42.2479921 0 6 42.4764961 0.03204186
GW 131 1 0 6 42.4764961 -6 0 42.705 0.03204186
GW 132 1 -6 0 42.705 0 -6 42.9335039 0.03204186
GW 133 1 0 -6 42.9335039 6 0 43.1620079 0.03204186
GW 134 1 6 0 43.1620079 0 6 43.3905118 0.03204186
GW 135 1 0 6 43.3905118 -6 0 43.6190157 0.03204186
GW 136 1 -6 0 43.6190157 0 -6 43.8474803 0.03204186
GW 137 1 0 -6 43.8474803 6 0 44.0759843 0.03204186
GW 138 1 6 0 44.0759843 0 6 44.3044882 0.03204186
GW 139 1 0 6 44.3044882 -6 0 44.5329921 0.03204186
GW 140 1 -6 0 44.5329921 0 -6 44.7614961 0.03204186
GW 141 1 0 -6 44.7614961 6 0 44.99 0.03204186
GW 142 1 6 0 44.99 0 6 45.2185039 0.03204186
GW 143 1 0 6 45.2185039 -6 0 45.4470079 0.03204186
GW 144 1 -6 0 45.4470079 0 -6 45.6755118 0.03204186
GW 145 1 0 -6 45.6755118 6 0 45.9040157 0.03204186
GW 146 1 6 0 45.9040157 0 6 46.1324803 0.03204186
GW 147 1 0 6 46.1324803 -6 0 46.3609843 0.03204186
GW 148 1 -6 0 46.3609843 0 -6 46.5894882 0.03204186
GW 149 1 0 -6 46.5894882 6 0 46.8179921 0.03204186
GW 150 1 6 0 46.8179921 0 6 47.0464961 0.03204186
GW 151 1 0 6 47.0464961 -6 0 47.275 0.03204186
GW 152 1 -6 0 47.275 0 -6 47.5035039 0.03204186
GW 153 1 0 -6 47.5035039 6 0 47.7320079 0.03204186
GW 154 1 6 0 47.7320079 0 6 47.9605118 0.03204186
GW 155 1 0 6 47.9605118 -6 0 48.1890157 0.03204186
GW 156 1 -6 0 48.1890157 0 -6 48.4175197 0.03204186
GW 157 1 0 -6 48.4175197 6 0 48.6459843 0.03204186
GW 158 1 6 0 48.6459843 0 6 48.8744882 0.03204186
GW 159 1 0 6 48.8744882 -6 0 49.1029921 0.03204186
GW 160 1 -6 0 49.1029921 0 -6 49.3314961 0.03204186
GW 161 1 0 -6 49.3314961 6 0 49.56 0.03204186
GW 162 1 6 0 49.56 0 6 49.7885039 0.03204186
GW 163 1 0 6 49.7885039 -6 0 50.0170079 0.03204186
GW 164 1 -6 0 50.0170079 0 -6 50.2455118 0.03204186
GW 165 1 0 -6 50.2455118 6 0 50.4740157 0.03204186
GW 166 1 6 0 50.4740157 0 6 50.7024803 0.03204186
GW 167 1 0 6 50.7024803 -6 0 50.9309843 0.03204186
GW 168 1 -6 0 50.9309843 0 -6 51.1594882 0.03204186
GW 169 1 0 -6 51.1594882 6 0 51.3879921 0.03204186
GW 170 1 6 0 51.3879921 0 6 51.6164961 0.03204186
GW 171 1 0 6 51.6164961 -6 0 51.845 0.03204186
GW 172 1 -6 0 51.845 0 -6 52.0735039 0.03204186
GW 173 1 0 -6 52.0735039 6 0 52.3020079 0.03204186
GW 174 1 6 0 52.3020079 0 6 52.5305118 0.03204186
GW 175 1 0 6 52.5305118 -6 0 52.7590157 0.03204186
GW 176 1 -6 0 52.7590157 0 -6 52.9874803 0.03204186
GW 177 1 0 -6 52.9874803 6 0 53.2159843 0.03204186
GW 178 1 6 0 53.2159843 0 6 53.4444882 0.03204186
GW 179 1 0 6 53.4444882 -6 0 53.6729921 0.03204186
GW 180 1 -6 0 53.6729921 0 -6 53.9014961 0.03204186
GW 181 1 0 -6 53.9014961 6 0 54.13 0.03204186
GW 182 1 6 0 54.13 0 6 54.3585039 0.03204186
GW 183 1 0 6 54.3585039 -6 0 54.5870079 0.03204186
GW 184 1 -6 0 54.5870079 0 -6 54.8155118 0.03204186
GW 185 1 0 -6 54.8155118 6 0 55.0440157 0.03204186
GW 186 1 6 0 55.0440157 0 6 55.2724803 0.03204186
GW 187 1 0 6 55.2724803 -6 0 55.5009843 0.03204186
GW 188 1 -6 0 55.5009843 0 -6 55.7294882 0.03204186
GW 189 1 0 -6 55.7294882 6 0 55.9579921 0.03204186
GW 190 1 6 0 55.9579921 0 6 56.1864961 0.03204186
GW 191 1 0 6 56.1864961 -6 0 56.415 0.03204186
GW 192 1 -6 0 56.415 0 -6 56.6435039 0.03204186
GW 193 1 0 -6 56.6435039 6 0 56.8720079 0.03204186
GW 194 1 6 0 56.8720079 0 6 57.1005118 0.03204186
GW 195 1 0 6 57.1005118 -6 0 57.3290157 0.03204186
GW 196 1 -6 0 57.3290157 0 -6 57.5574803 0.03204186
GW 197 1 0 -6 57.5574803 6 0 57.7859843 0.03204186
GW 198 1 6 0 57.7859843 0 6 58.0144882 0.03204186
GW 199 1 0 6 58.0144882 -6 0 58.2429921 0.03204186
GW 200 1 -6 0 58.2429921 0 -6 58.4714961 0.03204186
GW 201 1 0 -6 58.4714961 6 0 58.7 0.03204186
GW 202 1 6 0 58.7 0 6 58.9285039 0.03204186
GW 203 1 0 6 58.9285039 -6 0 59.1570079 0.03204186
GW 204 1 -6 0 59.1570079 0 -6 59.3855118 0.03204186
GW 205 1 0 -6 59.3855118 6 0 59.6140157 0.03204186
GW 206 1 6 0 59.6140157 0 6 59.8425197 0.03204186
GW 207 1 0 6 59.8425197 -6 0 60.0709843 0.03204186
GW 208 1 -6 0 60.0709843 0 -6 60.2994882 0.03204186
GW 209 1 0 -6 60.2994882 6 0 60.5279921 0.03204186
GW 210 1 6 0 60.5279921 0 6 60.7564961 0.03204186
GW 211 1 0 6 60.7564961 -6 0 60.985 0.03204186
GW 212 1 -6 0 60.985 0 -6 61.2135039 0.03204186
GW 213 1 0 -6 61.2135039 6 0 61.4420079 0.03204186
GW 214 1 6 0 61.4420079 0 6 61.6705118 0.03204186
GW 215 1 0 6 61.6705118 -6 0 61.8990157 0.03204186
GW 216 1 -6 0 61.8990157 0 -6 62.1274803 0.03204186
GW 217 1 0 -6 62.1274803 6 0 62.3559843 0.03204186
GW 218 1 6 0 62.3559843 0 6 62.5844882 0.03204186
GW 219 1 0 6 62.5844882 -6 0 62.8129921 0.03204186
GW 220 1 -6 0 62.8129921 0 -6 63.0414961 0.03204186
GW 221 1 0 -6 63.0414961 6 0 63.27 0.03204186
GW 222 1 6 0 63.27 0 6 63.4985039 0.03204186
GW 223 1 0 6 63.4985039 -6 0 63.7270079 0.03204186
GW 224 1 -6 0 63.7270079 0 -6 63.9555118 0.03204186
GW 225 1 0 -6 63.9555118 6 0 64.1840157 0.03204186
GW 226 1 6 0 64.1840157 0 6 64.4124803 0.03204186
GW 227 1 0 6 64.4124803 -6 0 64.6409843 0.03204186
GW 228 1 -6 0 64.6409843 0 -6 64.8694882 0.03204186
GW 229 1 0 -6 64.8694882 6 0 65.0979921 0.03204186
GW 230 1 6 0 65.0979921 0 6 65.3264961 0.03204186
GW 231 1 0 6 65.3264961 -6 0 65.555 0.03204186
GW 232 1 -6 0 65.555 0 -6 65.7835039 0.03204186
GW 233 1 0 -6 65.7835039 6 0 66.0120079 0.03204186
GW 234 1 6 0 66.0120079 0 6 66.2405118 0.03204186
GW 235 1 0 6 66.2405118 -6 0 66.4690157 0.03204186
GW 236 1 -6 0 66.4690157 0 -6 66.6974803 0.03204186
GW 237 1 0 -6 66.6974803 6 0 66.9259843 0.03204186
GW 238 1 6 0 66.9259843 0 6 67.1544882 0.03204186
GW 239 1 0 6 67.1544882 -6 0 67.3829921 0.03204186
GW 240 1 -6 0 67.3829921 0 -6 67.6114961 0.03204186
GW 241 1 0 -6 67.6114961 6 0 67.84 0.03204186
GW 242 1 6 0 67.84 0 6 68.0685039 0.03204186
GW 243 1 0 6 68.0685039 -6 0 68.2970079 0.03204186
GW 244 1 -6 0 68.2970079 0 -6 68.5255118 0.03204186
GW 245 1 0 -6 68.5255118 6 0 68.7540157 0.03204186
GW 246 1 6 0 68.7540157 0 6 68.9824803 0.03204186
GW 247 1 0 6 68.9824803 -6 0 69.2109843 0.03204186
GW 248 1 -6 0 69.2109843 0 -6 69.4394882 0.03204186
GW 249 1 0 -6 69.4394882 6 0 69.6679921 0.03204186
GW 250 1 6 0 69.6679921 0 6 69.8964961 0.03204186
GW 251 1 0 6 69.8964961 -6 0 70.125 0.03204186
GW 252 1 -6 0 70.125 0 -6 70.3535039 0.03204186
GW 253 1 0 -6 70.3535039 6 0 70.5820079 0.03204186
GW 254 1 6 0 70.5820079 0 6 70.8105118 0.03204186
GW 255 1 0 6 70.8105118 -6 0 71.0390157 0.03204186
GW 256 1 -6 0 71.0390157 0 -6 71.2674803 0.03204186
GW 257 1 0 -6 71.2674803 6 0 71.4959843 0.03204186
GW 258 1 6 0 71.4959843 0 6 71.7244882 0.03204186
GW 259 1 0 6 71.7244882 -6 0 71.9529921 0.03204186
GW 260 1 -6 0 71.9529921 0 -6 72.1814961 0.03204186
GW 261 1 0 -6 72.1814961 6 0 72.41 0.03204186
GW 262 1 6 0 72.41 0 6 72.6385039 0.03204186
GW 263 1 0 6 72.6385039 -6 0 72.8670079 0.03204186
GW 264 1 -6 0 72.8670079 0 -6 73.0955118 0.03204186
GW 265 1 0 -6 73.0955118 6 0 73.3239764 0.03204186
GW 266 1 6 0 73.3239764 0 6 73.5524803 0.03204186
GW 267 1 0 6 73.5524803 -6 0 73.7809843 0.03204186
GW 268 1 -6 0 73.7809843 0 -6 74.0094882 0.03204186
GW 269 1 0 -6 74.0094882 6 0 74.2379921 0.03204186
GW 270 1 6 0 74.2379921 0 6 74.4664961 0.03204186
GW 271 1 0 6 74.4664961 -6 0 74.695 0.03204186
GW 272 1 -6 0 74.695 0 -6 74.9235039 0.03204186
GW 273 1 0 -6 74.9235039 6 0 75.1520079 0.03204186
GW 274 1 6 0 75.1520079 0 6 75.3805118 0.03204186
GW 275 1 0 6 75.3805118 -6 0 75.6090157 0.03204186
GW 276 1 -6 0 75.6090157 0 -6 75.8375197 0.03204186
GW 277 1 0 -6 75.8375197 6 0 76.0659843 0.03204186
GW 278 1 6 0 76.0659843 0 6 76.2944882 0.03204186
GW 279 1 0 6 76.2944882 -6 0 76.5229921 0.03204186
GW 280 1 -6 0 76.5229921 0 -6 76.7514961 0.03204186
GW 281 1 0 -6 76.7514961 6 0 76.98 0.03204186
GW 282 1 6 0 76.98 0 6 77.2085039 0.03204186
GW 283 1 0 6 77.2085039 -6 0 77.4370079 0.03204186
GW 284 1 -6 0 77.4370079 0 -6 77.6655118 0.03204186
GW 285 1 0 -6 77.6655118 6 0 77.8940157 0.03204186
GW 286 1 6 0 77.8940157 0 6 78.1224803 0.03204186
GW 287 1 0 6 78.1224803 -6 0 78.3509843 0.03204186
GW 288 1 -6 0 78.3509843 0 -6 78.5794882 0.03204186
GW 289 1 0 -6 78.5794882 6 0 78.8079921 0.03204186
GW 290 1 6 0 78.8079921 0 6 79.0364961 0.03204186
GW 291 1 0 6 79.0364961 -6 0 79.265 0.03204186
GW 292 1 -6 0 79.265 0 -6 79.4935039 0.03204186
GW 293 1 0 -6 79.4935039 6 0 79.7220079 0.03204186
GW 294 1 6 0 79.7220079 0 6 79.9505118 0.03204186
GW 295 1 0 6 79.9505118 -6 0 80.1790157 0.03204186
GW 296 1 -6 0 80.1790157 0 -6 80.4075197 0.03204186
GW 297 1 0 -6 80.4075197 6 0 80.6359843 0.03204186
GW 298 1 6 0 80.6359843 0 6 80.8644882 0.03204186
GW 299 1 0 6 80.8644882 -6 0 81.0929921 0.03204186
GW 300 1 -6 0 81.0929921 0 -6 81.3214961 0.03204186
GW 301 1 0 -6 81.3214961 6 0 81.55 0.03204186
GW 302 1 6 0 81.55 0 6 81.7785039 0.03204186
GW 303 1 0 6 81.7785039 -6 0 82.0070079 0.03204186
GW 304 1 -6 0 82.0070079 0 -6 82.2355118 0.03204186
GW 305 1 0 -6 82.2355118 6 0 82.4640157 0.03204186
GW 306 1 6 0 82.4640157 0 6 82.6924803 0.03204186
GW 307 1 0 6 82.6924803 -6 0 82.9209843 0.03204186
GW 308 1 -6 0 82.9209843 0 -6 83.1494882 0.03204186
GW 309 1 0 -6 83.1494882 6 0 83.3779921 0.03204186
GW 310 1 6 0 83.3779921 0 6 83.6064961 0.03204186
GW 311 1 0 6 83.6064961 -6 0 83.835 0.03204186
GW 312 1 -6 0 83.835 0 -6 84.0635039 0.03204186
GW 313 1 0 -6 84.0635039 6 0 84.2920079 0.03204186
GW 314 1 6 0 84.2920079 0 6 84.5205118 0.03204186
GW 315 1 0 6 84.5205118 -6 0 84.7490157 0.03204186
GW 316 1 -6 0 84.7490157 0 -6 84.9774803 0.03204186
GW 317 1 0 -6 84.9774803 6 0 85.2059843 0.03204186
GW 318 1 6 0 85.2059843 0 6 85.4344882 0.03204186
GW 319 1 0 6 85.4344882 -6 0 85.6629921 0.03204186
GW 320 1 -6 0 85.6629921 0 -6 85.8914961 0.03204186
GW 321 1 0 -6 85.8914961 6 0 86.12 0.03204186
GW 322 1 6 0 86.12 0 6 86.3485039 0.03204186
GW 323 1 0 6 86.3485039 -6 0 86.5770079 0.03204186
GW 324 1 -6 0 86.5770079 0 -6 86.8055118 0.03204186
GW 325 1 0 -6 86.8055118 6 0 87.0340157 0.03204186
GW 326 1 6 0 87.0340157 0 6 87.2625197 0.03204186
GW 327 1 0 6 87.2625197 -6 0 87.4909843 0.03204186
GW 328 1 -6 0 87.4909843 0 -6 87.7194882 0.03204186
GW 329 1 0 -6 87.7194882 6 0 87.9479921 0.03204186
GW 330 1 6 0 87.9479921 0 6 88.1764961 0.03204186
GW 331 1 0 6 88.1764961 -6 0 88.405 0.03204186
GW 332 1 -6 0 88.405 0 -6 88.6335039 0.03204186
GW 333 1 0 -6 88.6335039 6 0 88.8620079 0.03204186
GW 334 1 6 0 88.8620079 0 6 89.0905118 0.03204186
GW 335 1 0 6 89.0905118 -6 0 89.3190157 0.03204186
GW 336 1 -6 0 89.3190157 0 -6 89.5475197 0.03204186
GW 337 1 0 -6 89.5475197 6 0 89.7759843 0.03204186
GW 338 1 6 0 89.7759843 0 6 90.0044882 0.03204186
GW 339 1 0 6 90.0044882 -6 0 90.2329921 0.03204186
GW 340 1 -6 0 90.2329921 0 -6 90.4614961 0.03204186
GW 341 1 0 -6 90.4614961 6 0 90.69 0.03204186
GW 342 1 6 0 90.69 0 6 90.9185039 0.03204186
GW 343 1 0 6 90.9185039 -6 0 91.1470079 0.03204186
GW 344 1 -6 0 91.1470079 0 -6 91.3755118 0.03204186
GW 345 1 0 -6 91.3755118 6 0 91.6040157 0.03204186
GW 346 1 6 0 91.6040157 0 6 91.8325197 0.03204186
GW 347 1 0 6 91.8325197 -6 0 92.0609843 0.03204186
GW 348 1 -6 0 92.0609843 0 -6 92.2894882 0.03204186
GW 349 1 0 -6 92.2894882 6 0 92.5179921 0.03204186
GW 350 1 6 0 92.5179921 0 6 92.7464961 0.03204186
GW 351 1 0 6 92.7464961 -6 0 92.975 0.03204186
GW 352 1 -6 0 92.975 0 -6 93.2035039 0.03204186
GW 353 1 0 -6 93.2035039 6 0 93.4320079 0.03204186
GW 354 1 6 0 93.4320079 0 6 93.6605118 0.03204186
GW 355 1 0 6 93.6605118 -6 0 93.8890157 0.03204186
GW 356 1 -6 0 93.8890157 0 -6 94.1174803 0.03204186
GW 357 1 0 -6 94.1174803 6 0 94.3459843 0.03204186
GW 358 1 6 0 94.3459843 0 6 94.5744882 0.03204186
GW 359 1 0 6 94.5744882 -6 0 94.8029921 0.03204186
GW 360 1 -6 0 94.8029921 0 -6 95.0314961 0.03204186
GW 361 1 0 -6 95.0314961 6 0 95.26 0.03204186
GW 362 1 6 0 95.26 0 6 95.4885039 0.03204186
GW 363 1 0 6 95.4885039 -6 0 95.7170079 0.03204186
GW 364 1 -6 0 95.7170079 0 -6 95.9455118 0.03204186
GW 365 1 0 -6 95.9455118 6 0 96.1740157 0.03204186
GW 366 1 6 0 96.1740157 0 6 96.4024803 0.03204186
GW 367 1 0 6 96.4024803 -6 0 96.6309843 0.03204186
GW 368 1 -6 0 96.6309843 0 -6 96.8594882 0.03204186
GW 369 1 0 -6 96.8594882 6 0 97.0879921 0.03204186
GW 370 1 6 0 97.0879921 0 6 97.3164961 0.03204186
GW 371 1 0 6 97.3164961 -6 0 97.545 0.03204186
GW 372 1 -6 0 97.545 0 -6 97.7735039 0.03204186
GW 373 1 0 -6 97.7735039 6 0 98.0020079 0.03204186
GW 374 1 6 0 98.0020079 0 6 98.2305118 0.03204186
GW 375 1 0 6 98.2305118 -6 0 98.4590157 0.03204186
GW 376 1 -6 0 98.4590157 0 -6 98.6874803 0.03204186
GW 377 1 0 -6 98.6874803 6 0 98.9159843 0.03204186
GW 378 1 6 0 98.9159843 0 6 99.1444882 0.03204186
GW 379 1 0 6 99.1444882 -6 0 99.3729921 0.03204186
GW 380 1 -6 0 99.3729921 0 -6 99.6014961 0.03204186
GW 381 1 0 -6 99.6014961 6 0 99.83 0.03204186
GW 382 1 6 0 99.83 0 6 100.058504 0.03204186
GW 383 1 0 6 100.058504 -6 0 100.287008 0.03204186
GW 384 1 -6 0 100.287008 0 -6 100.515512 0.03204186
GW 385 1 0 -6 100.515512 6 0 100.743976 0.03204186
GW 386 1 6 0 100.743976 0 6 100.97252 0.03204186
GW 387 1 0 6 100.97252 -6 0 101.200984 0.03204186
GW 388 1 -6 0 101.200984 0 -6 101.429488 0.03204186
GW 389 1 0 -6 101.429488 6 0 101.657992 0.03204186
GW 390 1 6 0 101.657992 0 6 101.886496 0.03204186
GW 391 1 0 6 101.886496 -6 0 102.115 0.03204186
GW 392 1 -6 0 102.115 0 -6 102.343504 0.03204186
GW 393 1 0 -6 102.343504 6 0 102.572008 0.03204186
GW 394 1 6 0 102.572008 0 6 102.800512 0.03204186
GW 395 1 0 6 102.800512 -6 0 103.028976 0.03204186
GW 396 1 -6 0 103.028976 0 -6 103.25752 0.03204186
GW 397 1 0 -6 103.25752 6 0 103.485984 0.03204186
GW 398 1 6 0 103.485984 0 6 103.714488 0.03204186
GW 399 1 0 6 103.714488 -6 0 103.942992 0.03204186
GW 400 1 -6 0 103.942992 0 -6 104.171496 0.03204186
GW 401 1 0 -6 104.171496 6 0 104.4 0.03204186
GW 402 1 6 0 104.4 0 6 104.628504 0.03204186
GW 403 1 0 6 104.628504 -6 0 104.857008 0.03204186
GW 404 1 -6 0 104.857008 0 -6 105.085512 0.03204186
GW 405 1 0 -6 105.085512 6 0 105.314016 0.03204186
GW 406 1 6 0 105.314016 0 6 105.54248 0.03204186
GW 407 1 0 6 105.54248 -6 0 105.770984 0.03204186
GW 408 1 -6 0 105.770984 0 -6 105.999488 0.03204186
GW 409 1 0 -6 105.999488 6 0 106.227992 0.03204186
GW 410 1 6 0 106.227992 0 6 106.456496 0.03204186
GW 411 1 0 6 106.456496 -6 0 106.685 0.03204186
GW 412 1 -6 0 106.685 0 -6 106.913504 0.03204186
GW 413 1 0 -6 106.913504 6 0 107.142008 0.03204186
GW 414 1 6 0 107.142008 0 6 107.370512 0.03204186
GW 415 1 0 6 107.370512 -6 0 107.599016 0.03204186
GW 416 1 -6 0 107.599016 0 -6 107.82748 0.03204186
GW 417 1 0 -6 107.82748 6 0 108.055984 0.03204186
GW 418 1 6 0 108.055984 0 6 108.284488 0.03204186
GW 419 1 0 6 108.284488 -6 0 108.512992 0.03204186
GW 420 1 -6 0 108.512992 0 -6 108.741496 0.03204186
GW 421 1 0 -6 108.741496 6 0 108.97 0.03204186
GW 422 1 6 0 108.97 0 6 109.198504 0.03204186
GW 423 1 0 6 109.198504 -6 0 109.427008 0.03204186
GW 424 1 -6 0 109.427008 0 -6 109.655512 0.03204186
GW 425 1 0 -6 109.655512 6 0 109.884016 0.03204186
GW 426 1 6 0 109.884016 0 6 110.11248 0.03204186
GW 427 1 0 6 110.11248 -6 0 110.340984 0.03204186
GW 428 1 -6 0 110.340984 0 -6 110.569488 0.03204186
GW 429 1 0 -6 110.569488 6 0 110.797992 0.03204186
GW 430 1 6 0 110.797992 0 6 111.026496 0.03204186
GW 431 1 0 6 111.026496 -6 0 111.255 0.03204186
GW 432 1 -6 0 111.255 0 -6 111.483504 0.03204186
GW 433 1 0 -6 111.483504 6 0 111.712008 0.03204186
GW 434 1 6 0 111.712008 0 6 111.940512 0.03204186
GW 435 1 0 6 111.940512 -6 0 112.168976 0.03204186
GW 436 1 -6 0 112.168976 0 -6 112.39752 0.03204186
GW 437 1 0 -6 112.39752 6 0 112.625984 0.03204186
GW 438 1 6 0 112.625984 0 6 112.854488 0.03204186
GW 439 1 0 6 112.854488 -6 0 113.082992 0.03204186
GW 440 1 -6 0 113.082992 0 -6 113.311496 0.03204186
GW 441 1 0 -6 113.311496 6 0 113.54 0.03204186
GW 442 1 6 0 113.54 0 6 113.768504 0.03204186
GW 443 1 0 6 113.768504 -6 0 113.997008 0.03204186
GW 444 1 -6 0 113.997008 0 -6 114.225512 0.03204186
GW 445 1 0 -6 114.225512 6 0 114.454016 0.03204186
GW 446 1 6 0 114.454016 0 6 114.68248 0.03204186
GW 447 1 0 6 114.68248 -6 0 114.910984 0.03204186
GW 448 1 -6 0 114.910984 0 -6 115.139488 0.03204186
GW 449 1 0 -6 115.139488 6 0 115.367992 0.03204186
GW 450 1 6 0 115.367992 0 6 115.596496 0.03204186
GW 451 1 0 6 115.596496 -6 0 115.825 0.03204186
GW 452 1 -6 0 115.825 0 -6 116.053504 0.03204186
GW 453 1 0 -6 116.053504 6 0 116.282008 0.03204186
GW 454 1 6 0 116.282008 0 6 116.510512 0.03204186
GW 455 1 0 6 116.510512 -6 0 116.739016 0.03204186
GW 456 1 -6 0 116.739016 0 -6 116.96748 0.03204186
GW 457 1 0 -6 116.96748 6 0 117.195984 0.03204186
GW 458 1 6 0 117.195984 0 6 117.424488 0.03204186
GW 459 1 0 6 117.424488 -6 0 117.652992 0.03204186
GW 460 1 -6 0 117.652992 0 -6 117.881496 0.03204186
GW 461 1 0 -6 117.881496 6 0 118.11 0.03204186
GS 0 0 0.0254 ' All in in.
GE 1
EK
LD 4 1 1 1 10 0
EX 0 1 1 0 1 0
GN 1
FR 0 1 0 0 1.706 0
Ermi,
The ARRL Antenna Handbook says this about helical antennas. Apparently formulas aren't available or applicable to helical antennas, but the key seems to be you can achieve near resonance by using a total wire length equal to 1/2 wavelength (288 ft at 1.7 MHz) spread evenly over the 3 meter antenna length. Adjusting a real helical antenna to resonance would be tedious, but might appeal to experimenters. ARRL suggests a small top hat to reduce voltage at the top below the corona/burn level at the top for 1000W transmitters. That's not a concern for us, but a small single-wire top hat would provide a way to fine tune for resonance.
ARRL Antenna Handbook:
"There is no hard-and-fast formula for determining
the amount of wire needed to establish resonance in a helical
antenna. The relationship between the length of wire
needed for resonance and a full quarter wave at the desired
frequency depends on several factors. Some of these are wire
size, diameter of the turns, and the dielectric properties of
the form material, to name a few. Experience has indicated
that a section of wire approximately one half wavelength
long, wound on an insulating form with a linear pitch (equal
spacing between turns) will come close to yielding a resonant
quarter wavelength. Therefore, an antenna for use on
160 meters would require approximately 260 feet of wire,
spirally wound on the support.
No specific rule exists concerning the size or type of
wire one should use in making a helix. Larger wire sizes are,
of course, preferable in the interest of minimizing I2R losses
in the system. For power levels up to 1000 W it is wise to use
a wire size of #16 or larger. Aluminum clothesline wire is
suitable for use in systems where the spacing between turns
is greater than the wire diameter. Antennas requiring close spaced turns can be made from enameled magnet wire or #14
vinyl jacketed, single-conductor house wiring stock. Every
effort should be made to keep the turn spacing as large as is
practical to maximize efficiency".
Medhurst and NEC-2 agree for a fatter helical monopole over ground--3 m in diameter, 3m high, 7 turns. Resonant frequency is just below 1.6 MHz with both analysis techniques.
NEC-2 guidelines recommend a loop circumference of at least .05 wavelengths. The 1-foot diameter helix is well below this guideline at at 1.6 MHz, while the 3-m diameter exceeds it.
If anybody is interested in downloading Medhurst's paper, it is linked (in two parts) on the following web page:
http://www.g3ynh.info/zdocs/refs/Medhurst/Medhurst1947.html
Ermi,
What is your source for the statement: "NEC-2 guidelines recommend a loop circumference of at least .05 wavelengths"? I couldn't find it in the NEC-2 Manual.