Thanks
Length of wire in the coil
= (π × dia of coil x number of turns) + height of coil
= (π × 5mm ×16 turns) + 53mm = 251mm + 53mm = 304 mm
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I also just noticed that there’s one measurement missing. The distance between the two vertical elements is 6mm, the same as the distance of the feed point from the bottom.
/edit - You’re either building one or modelling it right now, aren’t you?
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Edit:
Above test was for a Super J with stub.
Your design is super J with coil. I am not making/simulating your version right now, but may do when find time.
Just finished the modelling/simulation of your “Super J-Pole with Coil” design
Gain = 5.05 dB
SWR = 1.65
Coax connected at 6mm from bottom
Click on image to see larger size
Click again to see full size
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Thanks 
I assume that’s dBi? Those lobes are quite interesting.
Not sure, will check settings of simulation software.
The simulation is with setting “free space”.
If I use it with setting above “real ground”(say 7m/20ft), the lower half of lobe is flattened.
I’m not proficient with the software used but I would have assumed that the radiation pattern of such an antenna would have been symmetrical about the Z axis. Why in this model are they different around both the X and Z axis?
I was assuming that this was a coaxial colinear antenna made of two half wave elements joined by a halfwave phase shift coil which should result in a symetrical pattern about the Z axis.
Are you saying that mounting this antenna about 25 wavelengths above ground will affect the gain?
Thanks,
S.
@SweetPea11
I will again do the simulation with the same model, but instead of “free space” will use 21ft/7m above “real ground” and post the results. Gain will not be affected much, but radiation pattern will change. Please wait.
I think it’s set to near field and due to that, the J-Pole is asymmetrical because of the U at the bottom.
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The “U” at the bottom is an impedance match to match the impedance of the feed, in this case the coax, to the impedance of the antenna; in this case the high impedance end of the half wave radiator.
The “U” is a λ/4 parallel line shorted at one end and therefore the current in each wire should be equal and opposite to the current in the other wire thus cancelling each other out and not radiating.
As it does not radiate it should not be part of the model.
This video explains.
Note he called the half wave radiator a dipole.
S
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Near field is the critical thing here.
If you are close enough, they don’t cancel each other out.
in my case my horribile antenna didn’t improve the reception, still better with cutted stock antenna.
@nikka93
Except for 1/4 wavelength whip with ground plane (mag-mount base, or radials, or plate), all other designs made by DIY hobbyist are a “shot in dark”. Mostly failure, occasionally successful.
They are successful when made in a factory environment: Using precision metalwork tools, templates, elaborate test equipment and trained technicians.
Removed U from the model, and the lobes are still almost same.
This shows simulation does cancel the current in two parallel limbs of U, and treats it as non-radiating.
Another effect of removing U is that the SWR jumped up from 1.6 to 20
Click on image to see larger size
Actually the lobes are symmetrical now when they weren’t before.
Can you do the original design again and make sure you select “Far Field” ?
There is an entry in the top bar for it in the “Pattern” window.
I ALWAYS select far field when generating simulation.
All the simulations I have posted are with “far field” setting.
Pattern generated by selecting “Far Field”
Pattern Generated by selecting setting “Near Field”
OBSERVATIONS:
(1) The unsymetry is not severe.
(2) The unsymetry is caused by the stub as there is an unbalanced 6mm bottom part of U.
(3) Please see my last post. I have done simulation with Horizontal U, and unsymytry is still there.
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@abcd567 , looking at the 20.2 SWR, is it possible that would improve by using -45 angle radials in the model ? I have wire on the workbench today, I just may try one of these designs for grins … 
I just need to push aside a few dozen previous bits and pieces of “fine craftsmanship” to make room to work… 
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When radials, instead of being horizontal, are bent down 45°, the SWR improves from 20 to 18. Not enough improvement
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Don’t get too excited by simulation results. When model is built, the performance may be much less than what is shown in simulation. The reason is accuracy. For 2 meters (144 Mhz) or 4 meters (70 Mhz) antenna, few mm +/- wont matter. For 0.3 meters (1090 Mhz) antenna, few mm +/- means disaster.
Click on image to see larger size
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Any one interested to run simulation himself/herself, can download my model files from DropBox and run in software 4NEC2.
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