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Fat EFHW
- Thread starter HomerBB
- Start date
Homer, even today at 76 years old and mostly dilapidated, I can still put up my EFHW in about 15 minutes, if I don't go high.
Does it respond differently from your skinny version?
My old radio mentor use to tell me...increased diameter on an antenna allows a little more physical surface area for the element, and can show a small increase in gain, bandwidth, and it has a little effect on the resonant frequency.
Was he right?
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Homer, even today at 76 years old and mostly dilapidated, I can still put up my EFHW in about 15 minutes, if I don't go high.
Does it respond differently from your skinny version?
My old radio mentor use to tell me...increased diameter on an antenna allows a little more physical surface area for the element, and can show a small increase in gain, bandwidth, and it has a little effect on the resonant frequency.
Was he right?
Now that I have built it in 30 minutes, I can put it up in 5 minutes.
I need to send my MFJ-259b in for repairs so I can not give the best answer except for what I see with SWR meter. It shows greater than usual bandwidth for my home brew EFHW antennas. The center frequently is difficult to determine because it is so flat so wide on the band being useful through the 10 and 11 meters band and more both above and below CB.
Gain is not detectable of it is there in an increased amount, but i make contacts with it.
Dimensions:
16' 8" long.
1-3/8" diameter
fed at bottom with the matcher I made and I've been using on every efhw from wire to this one for months.
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A larger diameter antenna should not show a y additional gain over a skinny one other than imperceptibly lower IR losses amounting to a fraction of a dB. It should exigit a slightly wider bandwidth and be physically a bit shorter than a skinny antenna of the same design.
Although a half wave antenna has far lower ground loss it can still benefit from the addition of radials. It wil lower the take off angle somewhat as well.
Homer here are some results I took off a horizontal center fed dipole model I had, using .50", 1.00", and 1.50" diameter for the radiator. Looks like everything changes a little bit except the gain/angle
View attachment Homer's differences in radiator diameter.pdf
View attachment Homer's differences in radiator diameter.pdf
I decided to model a half wave with no radials, then copied it and added 1/4 wavelength radials to the copy and compared the two, this is what I got...
Note: The red plot is from the model with radials, the blue plot is from the model without radials.
I don't see much difference so I raised the height of the models...
Still not much of a difference...
Looking at the models I noticed something...
I see next to no currents on the radials themselves. If I change the length of the vertical element either direction (longer or shorter) it isn't long before currents on the radials begin to rise, but near the half wavelength point of the vertical the quarter wavelength radials have next to no currents flowing on them. As there is next to no currents flowing on them it is almost like they aren't even there.
About the only benefit I see adding radials is the model with radials has a slightly closer natural match, but even at that, the mismatch is still extremely high as would be expected with a half wavelength end fed antenna...
So I ask again, why bother with the radials?
The DB
I decided to model a half wave with no radials, then copied it and added 1/4 wavelength radials to the copy and compared the two, this is what I got...
Note: The red plot is from the model with radials, the blue plot is from the model without radials.
I don't see much difference so I raised the height of the models...
Still not much of a difference...
Looking at the models I noticed something...
I see next to no currents on the radials themselves. If I change the length of the vertical element either direction (longer or shorter) it isn't long before currents on the radials begin to rise, but near the half wavelength point of the vertical the quarter wavelength radials have next to no currents flowing on them. As there is next to no currents flowing on them it is almost like they aren't even there.
About the only benefit I see adding radials is the model with radials has a slightly closer natural match, but even at that, the mismatch is still extremely high as would be expected with a half wavelength end fed antenna...
So I ask again, why bother with the radials?
The DB
DB, I've been claiming the same for a long time and maybe to little avail.
Here are two of my EFHW models at 18' feet with and without radials. I did not do an overlay, but you can see the patterns are very close like yours are, and the angle did not change. There is little to no currents shown on these radials either, at least I can't see any. My currents log might show some however.
View attachment DB's EFHW compared to mine..pdf
For me it is like the radials are not there, but I do see a noticeable reduction in the FP match, like the difference between 100> SWR to 30:1 SWR, so the radials are doing something.
Personally I would much rather deal with a natural match at 30:1 than one over 100:1 SWR.
There is so much I don't understand about modeling and antennas, but I get similar results to what your show here. Maybe someone can give us a link to an EFHW model that produces different results and proves the claims that radials are a benefit to an EFHW, and that adding radials also improves the TOA.
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i like to see more real world test results. imho these tell ya how it SHOULD performI decided to model a half wave with no radials, then copied it and added 1/4 wavelength radials to the copy and compared the two, this is what I got...
Note: The red plot is from the model with radials, the blue plot is from the model without radials.
I don't see much difference so I raised the height of the models...
Still not much of a difference...
Looking at the models I noticed something...
I see next to no currents on the radials themselves. If I change the length of the vertical element either direction (longer or shorter) it isn't long before currents on the radials begin to rise, but near the half wavelength point of the vertical the quarter wavelength radials have next to no currents flowing on them. As there is next to no currents flowing on them it is almost like they aren't even there.
About the only benefit I see adding radials is the model with radials has a slightly closer natural match, but even at that, the mismatch is still extremely high as would be expected with a half wavelength end fed antenna...
So I ask again, why bother with the radials?
The DB
in a perfect world. however thats not the case. real on air tests MIGHT differ
from this im curious if would help decouple the coax so its not acting like a antenna
[a issue with both the a99 and imax ]and maybe lower the floor noise level a bit.
another comparsion i did maco vs imax the maco recieve was much quieter
same with my sirio .im no antenna genious i only know what ive tried and seen
and its been my opinion that especially the a99 is a incomplete antenna without
radials,yet everything ive read tells me im wrong.i view the a99 as a below average
to average antenna at best.