Good catch on the wire diameter. Yes, the wire diameter makes a difference. All things equal, a fatter wire will have a wider bandwidth. Something else I noticed - my models are for bare copper wire, while in the photos your antenna appears to be covered in insulation. I assume this was foam-dielectric RG6 cable? Is there non-foam dielectric RG6? I'll admit, while I'm familiar with 50 ohm coax, I knew very little about RG6 75 ohm coax. Most ham radio gear is 50 ohms, and up until now I've not had much need for a 75 ohm coaxial cable.
The foam insulation will also make a difference. If I remember correctly, the insulation slows down the velocity of propagation, making the wire appear to be longer than it is. I will rework the models with both the smaller wire and the insulation added either tomorrow evening or over the weekend.
Unfortunately, I created the model of the 10mm closed stub version before I saw this post. However, for comparison purposes to my past models, I've decided to present the results anyways even though the wire diameter is wrong and the insulation is missing from the model.
I think the results are very interesting. And they agree with what abcd has noted during maximum range testing.
So here is the the closed stub diagram that I modeled:
Here is the model:
And the wire table:
RESULTS:
The SWR is not quite as good as the previous version. I did move the feedpoint from the 18mm shown above to 20mm, as that resulted in the minimum SWR. It was slightly higher at the 18mm point.
The pattern is a slightly different, with the same gain as my modified design presented earlier with the stubs removed, but slightly more gain than the original open-stub version:
DISCUSSION:
An SWR of 2.05 is still very respectable, with a loss of 0.55 dB. While the SWR loss is higher than abcd's original open-stub version, this antenna has more gain which overwhelms the additional loss. (9.82 dBi gain here versus 9.14, a increase of 0.68) The model confirms that this closed-stub antenna will perform better than the original open-stub version. This agrees with the maximum range test results presented earlier by abcd.
As I've noted earlier, this antenna should work very well for ADS-B reception.
thanks much and 73,
ben, kd5byb