Comparing Four Wire Antennas and Introductions to their Generic 4NEC2 Models (008h)

In this video I am going to be do two things:
1. I will introduce you to the Generic Modeling files for the Dipole/Inverted-Vee and the Folded Dipole/Folded Inverted-Vee antennas
2. I will use these two generic models to simulate four common wire antennas and compare their performance on several metrics.
The four antennas I will be comparing are:
1. The Dipole
2. The Folded Dipole
3. The Inverted-Vee
4. The Folded Inverted-Vee
The metrics I will be looking at include:
* Feedpoint Impedance
* Bandwidth
* Best SWR
* Radiation Efficiency
* Gain
* "Take-Off" Angle
* Beamwidth
I have provided the original modeling files and the Excel spreadsheet in a ZIP file for you. You will find the link to this file below.
=== PROMISED LINK ===
Modeling Files and the Excel Spreadsheet ZIP file
drive.google.com/file/d/1SD04...
Time Markers for Your Convenience
----------------------------
00:05 Introductory Comments
02:24 The Dipole: the simulation
02:39 The Characteristic Impedance = 75 Ohms
03:18 Introduction to the Symbols used in the Dipole Model
03:35 Set the Units: this file = feet
03:48 Step-by-Step Tour of the Symbols
06:20 Setting the Center Frequency, f
06:47 Optimize the Antenna Leg Lengths
07:06 Frequency Sweep & Data Export
07:22 Far Field Pattern & Data Grabbing
07:50 The Inverted-Vee: the simulation
07:57 Characteristic Impedance = 50 Ohms
08:04 Set the Angle of the Antenna Legs
08:49 Optimize the Antenna Leg Lengths
09:02 Frequency Sweep & Far Field Data Acquisition
09:11 Folded Antennas
09:14 What IS a Folded Antenna????
10:14 The Folded Dipole: the simulation
10:18 Characteristic Impedance = 300 Ohms
10:48 Introduction to the Symbols used in the Folded Antenna file
11:00 Set the Units: this file = feet
11:05 Tour of the Symbols
11:19 The NEW Symbol = "sep"
11:52 Configuring this Model for the Experiment
12:45 Optimize, Frequency Sweep, Far Field Pattern & Data Gathering
12:53 The Folded Inverted-Vee: the simulation
12:59 Characteristic Impedance = 200 Ohms
13:11 Configure the Model to be a Folded Inverted-Vee
13:39 Optimize, Frequency Sweep, Far Field Pattern & Data Gathering
13:44 OBSERVATIONS
13:53 Bandwidth
13:57 What do I mean by "Bandwidth?"
16:44 Best SWR
17:26 Radiation Efficiency
17:59 Gain
18:39 Take-Off Angle
20:24 Beamwidth
21:20 Conclusions
22:20 Final Comments and Toodle-oots
-----------------------------

[@garylanders1470]

Very interesting from my perspective also!

[@eie_for_you]

I thought so, too! 🙂

[@4X6GP]

One more thing to consider in choosing the antenna type: A simple dipole or inverted V can be used on both odd and even harmonics, with a tuner. But a folded dipole or V will not work on even harmonics.

[@eie_for_you]

You got me thinking because I have ALWAYS heard "odd harmonics only", so I did a little experiment here. Just from a frequency perspective ...
I tried 80/75m frequencies first as the fundamental. Only even harmonics hit other ham bands with the exception of the 17m band and the antenna would have to be tuned to the LOW end of the band to make this work.
So, I retried assuming a 40m antenna. From a frequency perspective, this was more promising. See these results in the document link below.
From an SWR perspective on a *real* antenna ...
Next, I connected my VNA up to my 40m inverted vee and scanned it from 7MHz to 50 MHz. Yes, I know it is tuned a bit high in the band, so this just verified what I already knew. I am looking for SWRs at harmonics of the fundamental. Here is what I discovered:
Harmonic Freq (MHz) VSWR
1 7.250 1.30 40m band
2 14.50 5.95 20m band
3 21.75 2.78 15m band
4 29.00 3.78 10m band
5 36.25 2.52 -- nowhere --
6 43.50 2.90 -- nowhere --
Here is a link to the document with the results:
docs.google.com/document/d/1ZD5ibBJV9QnHSeQH7TFLW_5p9lPWEPzo/edit?usp=sharing&ouid=113004549152926472999&rtpof=true&sd=true
So, I suppose it is possible to use the even harmonics, but the antenna's radiation efficiency has got to be abysmal. Additionally, with SWRs in the 6 range (20m band), we have 51% of our power being reflected back at the transmitter. The antenna tuner might make the transmitter happy, but it will not change the fact that we are throwing away 51% of our power in heat somewhere.
Thank you for your thought inducing comment.

[@4X6GP]

@@eie_for_you I disagree that you are "throwing away" any power due to SWR when the line is matched to the transmitter, except for the slight additional loss in the feedline due to SWR. Reflected power is reflected back and forth between the source and the load, and most of it ultimately reaches the load.
I have a rotary dipole 10m long, fed through about 10m of homemade open wire line, no. 12 wire spaced 10cm. It is matched to the transmitter by a link-coupled tuner, an old Johnson KW Matchbox. It works very well on all the bands from 40m to 10m (I had to make a slight mod to the matchbox so it would resonate on 30m). On 40, I calculate the loss due to the astronomical SWR as about 2 dB; on all other bands it's negligible, due to the low inherent loss of 10m of open line.

[@eie_for_you]

I had to noodle on this. True, the power does reflect back in the direction of the antenna and from the antenna back to the transmitter ("rattling back and forth"). 51% of all of the power arriving at the antenna comes back at the transmitter due to the mismatch; this is the re-reflected power + the transmitter power. It is also true that there is loss for each trip through the feedline. In the end, there is still appreciable loss which cannot be ignored.
We cannot forget the abysmal radiation inefficiency of an antenna at the even harmonics.
While we *could* use an antenna on an even harmonic in a pinch, I would *never* recommend this as normal operating.

[@4X6GP]

@@eie_for_you If the antenna is fed with low loss transmission line like open wire line, the loss can be very small. My dipole acts as two half waves in phase on 10 meters and it even has a little gain over a dipole. The extra loss in the feedline due to the SWR is negligible.
It even works on 40 meters, where the SWR is about 90:1! But since the feedline is short (only about 10m) and very low loss, the additional loss due to SWR is only about 2 dB.
In fact, the 1/4 wave feedline translates the impedance of the antenna, which has low resistance and is very capacitive, to a high resistance plus inductive reactance, which is much easier to efficiently match to the transmitter.
I agree with you that this would not work very well with a coax feedline.

[@eie_for_you]

Aaaaaah ... I am speaking to the average person who only feeds their antennas with coax and does not care to, or have the knowledge how to, do any such transformations. They just want to connect their antenna with some coax and be done with it. The setup you describe is very different than this scenario.

[@EI6DP]

I use a T2FD due to restricted space.

[@eie_for_you]

Aaaah! How well does that work for you?
I have a folded inverted vee for my 75/80 antenna. I created it because I was tired of the bandwidth limitations of the simple inverted vee (ua-cam.com/video/McbDL1GxbqI/v-deo.html).
I've heard of doing the termination thing, but I decided to keep it this way because I have the space for dedicated, single-band antennas. 🙂

[@EI6DP]

Hello - I find the T2FD one really great antenna, with a very low VSWR from 80m to 10m. There are one or two spots where the VSWR goes above 2.5:1 but my ATU easily sorts that out. I've been on the air for 40+ years and I have to say that the T2FD is the best antenna for restricted places.