3/4 vertical vs 1/4 vertical
I did some quick EZNEC plots for a 20 meter vertical (ground mounted). The first is a standard 1/4 wave and the second is a 3/4 wavelength as an inverted where the first 32 feet are vertical and the remain approximately 17 feet are horizontal.
The plots look interesting. It seems from what I'm seeing that the 3/4 wave vertical is up about 3 db over the 1/4 at 27 degrees and that gain persists holds down to about 15 degrees and lower. Only potential downside I can see is that I'll get more overhead atmospheric noise with the 3/4.
For a bit of background, I'm construction a 33' vertical support structure from 2 by 4 lumber, so it's just as easy to do the 3/4 as the 1/4.
Anybody agree? Disagree?
I don't do antenna modeling but usually a 3/4 wave vertical produces poor radiation angle for DX. 5/8 wave is about the upper limit on length for getting a low radiation angle.
deleted - misread the post
Or is it that the maximum take off angle is higher? From what I see, the gain is still pretty good at those lower angles. The pattern looks different on the FF plot, but the gain on the outer ring of the graph is about 3 db stronger and for a 1/4 wave element.
Maximum current also occurs in 2 spots - one being well away from ground losses. Benefit? Possibly.
As a side note, I currently my 40 meter vertical as a 3/4 vertical for 15 and it performs very well, but I don't have a 1/4 element for comparison. Sometimes my 15 meter dipole at 30 feet wins, sometimes the 3/4 vertical.
I show more gain difference than that, but the real answer depends on how much ground loss you have. Even the low angle gain is greater for the 3/4 wavelength inverted L. One disadvantage of the L is that it has a null in the direction the top wire runs away from the vertical one. However the gain of either of these antennas is less than that of a half wave dipole, at all elevation angles, at the height of the top wire of the L. The disadvantage of the dipole is that it has nulls off the ends.
The atmospheric noise is not likely to be a problem with either of these antennas. That noise is low on 20 meters and usually not much is arriving from high angles.
I was being conservative on the gain figure - I agree. Agree also on the gain of the dipole at the same height, but I'm thinking the 3/4 vertical is a good backup and fill-in antenna. I've got a ton of choice on which way to orient the horizontal portion, so that's not much of an issue.
Originally Posted by K4SAV
Height above ground, objects in the fresnel region, ground losses etc...
73 de Charles - KC8VWM
North American QRP CW Club #3159, SKCC# 5752
Actually, my 40 meter vertical is also an inverted L. Runs about 21 feet vertical and the rest is a bit less than horizontal - sloping slightly towards ground. Ground mounted with 16 radials.
This is just my comparison of my vertical 53' Hy Gain HyTower with good radial field and a OCFD 270' @ 55' on 20m and higher the OCFD works better "most" of the time but on the low bands 40/80m it's the vertical hands down even in directions favoring the wire.
Charles do you have both a vertical and a dipole? I know Glen does he has the same vertical I have. I wonder if others have this also between the two? I do use the vertical only for QRP on all bands and make contacts except for 80/160m have to wait for season.
If you have room try a dipole also to compaire the two.
73 de Fred N0AZZ
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