# Tag Info

5

Yes, being limited to 20 total segments for two dipoles is likely to be a problem, especially because of your hope / plan / expectation to have the model accurately predict what is built. I created an EZNEC model of a fan dipole for 40 and 20 meters; even the minimum segmentation - which, don't forget, must suffice at the highest operating frequency - ...

4

It is true that 4nec2 is a bit non-intuitive when it comes to creating a new antenna, but it is easy to start from scratch and create anything, without the need to import. 4nec2 provides 4 different methods to edit the antenna model and you can find them on the Settings menu. By default, the 'Nec Editor (new)' is selected but you can change it to 'Geometry ...

4

To answer this very graphically: Flipping the diagram geometrically can't work: What you've actually build is kind of a waveguide, consisting of two grounded planes below (earth) and above (virtual earth spanned by radials) your antenna; in this rotation-symmetrical setup, the H-field only exists in horizontal direction, and the E-field between the two ...

4

If you were to flip the antenna upside-down, ideally with no part of the antenna touching the ground, then your antenna radiation pattern wouldn't change all that much, as you've discovered on EZNEC. Two things have changed compared to a 'normal' ground-mounted vertical: you've elevated the radials, and you've flipped the antenna. (The following ...

4

The displayed radiation pattern is not a physical object in a meaningful spatial relation to the elements of the antenna, it's a graph of data. Consider the meaning of the (polar) coordinates of each: For the antenna model, $(r, \phi, \theta)$ are coordinates of the antenna structure elements. For the pattern graph, $(\phi, \theta)$ specify a direction away ...

4

Does this mean this antenna can't be tuned to the 160M band, or does this just mean that the impedance is so different from 300 ohms that the SWR is useless? A little bit of both. If you get an off-the-shelf matchbox, which is usually advertised as being good for a 10:1 range or even less, then you can expect that it won't be able to make this antenna do ...

3

When a dipole is less than a 1/4 wavelength above ground, the image antenna formed by the reflection from the ground creates destructive interference at low angles, making the antenna quite useless for DX. At 40 meters, a quarter wavelength is about 35 feet, more than the current 23 feet at apex. The effect will be diminished if you are not also able to ...

3

Without any insight into the design of your program, I can only offer some basic guidance. The parasitic elements in a yagi design are shorted dipoles that can also be modeled as a collection of infinitesimal dipoles. A shorted dipole will re-radiate nearly all of the power that it intercepts. This re-radiation will interact with the driven element. The ...

3

Would a useful representation be rotating the antenna 25 degrees to account for the terrain? I'd think so, as long as you also then rotate all the results 25 degrees in the opposite direction. I can't think of anything that actually wouldn't rotate with the ground (gravity, geomagnetic field, ...) that would have any significant effects. Does it really ...

3

Please see my graphic below. A λ/2, center-fed dipole has about 0.7 dB more gain than a λ/4 ground plane, but otherwise their v-pol, free-space radiation patterns are very similar. Whether the vertical conductor of a λ/4 ground plane is pointing to the zenith or the nadir, its radiation toward the earth would produce nearly the same reflections from the ...

3

An elevated "ground-plane" antenna with tuned radials has, by itself, a pattern much like a dipole doughnut shape (freespace is what I'm talking about at the moment). Unfortunately we must mount the antenna and feed it with a feedline. This introduces one or more additional conductors below the radials that demonstrably (via simulation and measurement) ...

3

4nec2 takes the radiation efficiency into account when it calculates the gain. You can see this for yourself by modeling an antenna made of copper and then writing down the gain, and then changing the antenna model to use a lossier material such as iron. So 6 dBi is 6 dBi no matter what the radiation efficiency of the antenna may be. To answer your ...

3

Rod, Ends of wires are connected if they are at the same location. Your model is correct in this regard. However, the wires need to be about one-quarter wavelength long rather than the full wavelength shown. The 4NEC2 software provides the Automatic Gain Test (AGT) check box when you Generate (F7) the results of your model. Use this in the early stages ...

3

I use Mathematica with NEC4 which would work essentially the same as with NEC2. I find Mathematica to be a great front end to NEC4 for not only graphing results but also preparing functions for various mathematical operations (i.e. doing Calculus with the resulting solutions). Originally, I created a notebook of various functions that I wrote to perform ...

3

I think if you're worried about the load on the other dipole, you need to go back and look at how Z parameters work. $Z_{21}$ doesn't assume anything about the impedance on the two dipoles. It's just one of the impedance parameter term - $Z_{21}$ is the voltage developed on dipole 2 due to a current in dipole 1. It's not the final voltage or current present ...

2

Recall that: Antenna system gain (efficiency) includes system r-f losses. If any exists, then a proportional amount of applied power from the transmitter is dissipated as heat in the lossy elements of that antenna system. The shape of the radiated envelope (relative fields) of that antenna system remains the same for all non-zero losses, but for other ...

2

I just did a bit of tinkering with 4NEC2 and I've got an answer. The Input power is the power generated by the source, and ignores all losses. It might also be called "Total power". The "Radiat-power" calculation in 4NEC2 is the total amount of the power from the source that is not dissipated as resistive losses in the feed system or antenna structure. ...

2

I'm a NEC2 user, never used 4NEC2, but I think it's the same engine underneath. The radiated efficiency is low because either: - a lot of power is absorbed by the ground, or - you have a structure error, usually a violation of the guidelines near the feedpoint. There are two ways of calculating efficiency. The first just considers the currents on the ...

2

It is more than 15 years ago, that I've done it. But if I remember correctly, the 3D screenshot you're showing is quite misleading. The pattern is drawn around the 1st antenna / center of coordinate system. Delete the 2nd antenna and compare the gains to make sure nothing changes at all.

2

In order to properly model an antenna in your example, you need to be very specific as to the type of antenna and its installation details. Once this is specified, the antenna can be modeled as a signal generator with a source impedance equal to the characteristic impedance of the antenna. If it is a common antenna with a typical installation, you may be ...

2

The small antenna is quite poor as a radiator because there is a dimension restrict for the device. It is important to separate cause and effect when designing antenna systems. Recall that the directivity of an infinitesimally small dipole has a directivity of 1.5 compared to a full size 1/2 wavelength dipole with a directivity of 1.64. That is less than a ...

2

@pymekrolimus: Below is a clip showing the details of a quick study of a model based on your posts so far. The NEC4.2 engine was used for the calculations. The results look close to what might be expected. The wire model showed no geometry or segment errors at runtime, and the AGT test returned a result of "perfect." The wire table is shown, should you ...

2

Good simulation work - your results look pretty realistic. A note about patterns - when you talk about Azimuth and Elevation patterns, with the antenna lying on its side, it's not completely clear which they are. Normally a folded dipole is installed standing up, so it's omnidirectional. In your model there are two elevation patterns: one at $\phi=0$ (the ...

2

The NEC4.2 analysis below compares the intrinsic fields/gains of the same monopole for the definitions and conditions shown in that graphic. Note that the monopole having a 10 Ω path connecting it to the ground plane does not display zero gain in the horizontal plane, then gradually rising to more positive values for greater elevation angles above the ...

2

Now I'm using the software 4nec2 (with wine) with the description from DL6GL. With this software you can generate the .out files. I hope to succeed.

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I doubt that the segment limits of the program is your main problem. You should get accurate enough details in spite of that. Part of the problem is at the feedpoint. You need to build your fan dipole so that there are insulating spreaders* to keep the wires for the different bands parallel and farther apart from each other for most of their length. As it ...

2

The answer to your question is on page 6 of Antenna simulations with 4NEC2 including an application example for 2300MHz: A symbol (SY), x, is defined as having the value 0.907. This value is used in the calculations for the lengths of the dipole arms in the following GW statement. I prefer doing this with the Symbols tab in 4NEC2's "NEC Editor (new)&...

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Years ago I used a simulation like this one for the same purpose. The antenna you refer to is a tuned antenna, so it is not wideband. The antenna that I made is a wideband, really flat response (conversion from field strength to output voltage is frequency-independent). Conclusion: the difficulty is the design of the low-noise amplifier. Depending on what ...

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If you need calibrated output then you probably won't be able to do it. That's why they are so expensive. It's like a \$20 SDR dongle versus a \$2,000 spectrum analyzer, with the most notable difference being that the spectrum analyzer is calibrated and tells you how much power is at each frequency. If you don't need calibrated output and just want to get a ...

1

Using a closed loop whose circumference is only about $\lambda$/4 puts it in the regime of a "small" transmitting loop. This online Small Transmitting Loop Antenna Calculator gives remarkably similar results to NEC simulation using only formulae from the ARRL Antenna Book. It's particularly interesting to observe the effects of increasing conductor diameter: ...

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