One of the reasons for this is that most designs are for QRP antennas and not made to handle more than 5 — 10 W of power. A couple of months ago, I ran across a design rated at W. The design seemed relatively simple to build, requiring only a single toroid and a capacitor made with a short length of RG coax.
Well, it just so happens that I bought ft. Sunday was a beautiful day here with temperatures in the 60s, so I decided to put up the antenna. The SWR is 2.
The guy in MA even gave me a signal report. I e-mailed the guy who published the design and asked why he thought the resonant frequency was so high, and he said that all I had to do was add a couple feet of wire to the antenna. He also suggested that adding a turn or two to the coil would bring the SWR down. I still do plan to try a counterpoise. Not so much to improve the SWR, but to see if it makes the antenna a little more efficient.
This is a very nice box. Not only is it completely enclosed. The screw down cover is gasketed, making it waterproof. Not only were they out of stock, when I searched their website for that part number, it came up with no results. I Googled the part number and found several places online that had them, but they wanted more money, plus I would have to pay shipping. Fortunately, I was able to find some at a local Home Depot.
Sure, end fed antennas have some advantages is erection, but there always seems to be a lot of RF on the feedlines of them. They are usually power limited, maybe a good thing, with all that stray RF floating around. He simply pulls it vertically up a tree limb. Since may of all of these EFHW antennas use the coax as a counterpoise, what is the minimum length that is required for the coax?
If I sit on my deck and put the matching box 2 feet from my qrp rig will it still give me the results that all these operator are stating? They are quite narrow band but ideal for outdoor portable use when the tuning unit is right next to you on the table with the radio.
Have fun experimenting!
Simulating the end-fed half-wave (EFHW) dipole antenna
I remember this from my short pants days c I also remember problems with unbalance in the feed currents on the two wires of the line causing problems getting a low SWR below 1. My meter Par now LNR end-fed is around 1. The feedpoint is about five feet off the ground, and the half-wave wire angles back to a tree in my yard.QRZ Forums.
An End-Fed Half-Wave which is 20 m long usually a little shorter than that will resonate on any band for which the wire is a multiple of a half wavelength, that is, 40 m, 20 m, 15 m, 10 m, 8.
In that sense it is a multiband antenna. The End-Fed Half-Wave has a primary attraction of needing a minimal counterpoise as the antenna impedance is very high compared to the counterpoise impedance, so that it is good for portable operations when one wants to have the antenna element mostly vertical for good low-angle take off and the counterpoise lying on the ground where its small amount of radiation and power is not likely to contribute much to the antenna radiation.
KW4TIJul 23, W6OGCJul 24, NH7RO likes this. What's Better? Endfed or Dipole Your endfed is more than a few quarterwaves long at 10 or 15M will have many lobes going in different directions and will be strong in some directions and weak in others, The halfwave dipole is bidirectional with two main lobes broadside if up high enough. Hard to say what will be better in what directions. It's A trick question. K8JDJul 24, KG5BJV likes this.
End-Fed Half-Wave antennas, Grounding & RF Chokes
Here are the loss results: 3. A pf cap was shunted across the input 50 ohm side. I tested the UnUn at watts and use a thermal heat gun to see if the core got warm, "It did not! In the beginning, I was not impressed with EF antennas. After doing the research and testing different ideas, I found the above design to work great. My EF is 65 feet 6 inches of insulated 18 wire. No tuner is needed on 7, 14, 21 and 28 mhz. But keep in mind, I only operate in the CW portion of the band. If you are considering trying an EF, try the above design.
It's test proven and it works great. KU3XJul 24, Uh Oh! I read the wrong chart. Here is the updated chart for my UnUn losses 3. It all fits in a tiny pouch I picked up in the tool department of Home Depot.
How did you test the losses? Did you do a through test with two identically wound ununs or look at the return loss from one unun? A shorted secondary return loss measurement unfortunately doesn't necessarily take into account the losses of the shunt impedance of the transformer because it is shorted outwhich is a major cause of the transformer losses.
Also, ferrite can take a while to heat, but if you were key down for a while and didn't detect any heating that is pretty good. Did you use a W 3 kohm dummy load, or a 50 ohm dummy load with two ununs back-to-back? I measured my design using a through test of two ununs. I was able to get about 1 dB of loss at 28 MHz. I changed the winding pattern a bit to help reduce the leakage inductance, and added an adjustable air variable capacitor to allow tuning over a very wide range.
It can be quite easy to get a transformer matching a high output impedance to match its own shunt impedance, therefore efficiently heating the core rather than radiating, so this is a concern as well.When you subscribe, you receive only messages for the product you have subscribed to.
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Electrically isolated end-fed vs. center-fed dipole radiation
Reviews Home. As others have said very easy to install. Transformer is mounted on a side of a tree 3 feet above ground and ground wire is about 4 ft long. A Radioworks line isolator is installed at the midpoint of the coax feed. The antenna is hung in an inverted V. After reading that an inverted V fed at one end is a low angle radiator on the harmonics I can atest this is true. This set-up is a great DX antenna and on 40 i'm getting "great signal" reports.
After cutting off 1 foot of wire my swr on 40M is 1. It is also a very quiet antenna and in my location much appreciated. From K1RF: "But a key characteristic that does change is the radiation pattern on each harmonic.Navigation Menu. What happens as the slope of a dipole changes? Figure 1. Figure 2. What happens to the radiation pattern? Figure 4. Having only a single vertical support or limited horizontal space might be a problem. Such a problem can be solved by mounting a dipole at a slope.
This is a common antenna configuration in the world of amateur radio referred to as a "Sloper" or more accurately, "Half-Wave Sloper". To help make a decision about using a sloped dipole "Sloper", you need to know The answers are most quickly found by antenna modeling. A choke balun at the feed point is advised. For each model run, the slope angle is set and the software Optimization function finds, by iteration, the length of resonant wire that produced the best SWR and X-in impedance values at the desired frequency.
The study was conducted in steps of 10 degrees. Figure 1 It appears that there are three regions.
Efficiency is half. Gain is less than half. Drop-off is rapid. The antenna end comes very near to the ground. Figure 2 First: There is an oddity at a slight slope. The Red graph line rises.
The resonant length is slightly longer! Presumably this because the antenna is closer to ground at one end therefore not quite symetrical to reflected RF.
Second: Following the Red line. The low point starts at 69 Ohms 1. To help visualized the radiation, the antenna modeling software has the ability to selectively display the Horizontal GainVertical Gain.Navigation Menu. What Happens If Multi-band Operation Any length of wire has a resonant frequency.
Think of a guitar string. If you touch it in the middle you now have two halves at twice the frequency. Touch at one-third you get three sections at three times the resonant frequency.
At one-fourth, get four sections at four times the resonant frequency, et cetera. These are harmonics. Starting with a wire that resonates at 80 meters 3. Antenna modeling shows that a resonant half wave wire can be fed at any point End, Off-Center, Center without changing gain or efficiency Away from center, impedance is high so a transformer is used to match an antenna to coaxial cable.
At this point the Standard Deviation between those seven resonant length's is only 0. These can be aligned with the 1st harmonic by using a small inductance and capacitance.
The general rule is to position an antenna is "as high as wide". This halfwave elevation provides the maximum signal to the sides with minimum signal skyward. No feedline is considered. A round reflection dome develops between each half-wavelength.
As seen from the table, an 80 meter antenna at half-Wavelength Height should be at This is impossible for most amateur radio operators, therefore the modeling data that follows is based on a This is a practical maximum for commercial masts, telescoping poles and trees.
You can use the above 4NEC2 antenna model to see what happens at specific elevations and bands. Model Data by Harmonic The following data are for the far field radiation patterns and 3D color views of an End Fed Half Wave Inverted-V antenna with the high point in the center at 40 feet and the ends about 10 feet over ground.
The direction of radiation is the Blue trace on the polar graphs. On the 3D views the Red color indicates the stronger radiation.QRZ Forums. Tags: 80m efhw end fed half wave inverted l. The antenna is set up as an Inverted-L and seems to be working great despite the poor conditions everyone says we're experiencing right now.
It got me onto 80m on evenings when there aren't many thunderstorms and led me to "discover" 20m. It seems to work as well on 40m as my 40m folded dipole did, though I don't have them both up at the same time to compare back-to-back. On 10m, switching between this antenna and an Imax is a toss-up depending on the location of the other station. I don't have much man-made local noise; I live in the country with the nearest neighbor roughly a half-mile away on the other side of a hill.
I've shut power off at the pole which made a negligible difference with regards to noise, unfortunately. My question is, should I set the antenna up as an Inverted-L or a "flat top" horizontal antenna?
I have enough horizontal space between my antenna supports to make it fully horizontal but would like to have some low-angle radiation on 80 and 40m.
I will eventually be adding an additional 15 to 20 feet of height on one end and 10 feet to the other. I don't have any ground radials.
Thanks for any suggestions. On 80 M, it doesn't make much difference, unless you can get a height of 60 or 70 ft or so. The picture isn't quite so bad on 40 M, where about 30 ft of height is needed at the e"L"bow point. This, however, puts performance on 80 M down a few dB at 20 degrees. Last edited: Jun 20, KD6RFJun 20, KD0WQP likes this. Ok, that's exactly what I needed to know. Many thanks! Mine is inverted L at about 65ft.QRZ Forums. Hi, My shack living in a highly antenna restricted community is on the 2nd floor of our house and I don't have RF grounding gasp!
I have been told that such an arrangement may also be counter-productive, but mileage may vary depending on the set-up in general. The feed-point was about 4' above ground, sitting outside on a window "ledge". I did not have any grounding our counter-poise at the feed-point nor did I have any current balun or RF choke anywhere in the feed-line. And, yes, I ended up having a lot of RFI in the shack, especially when using higher duty-cycle modes such as CW even when putting out W.Dipole, EFHW, Vertical, Windom antenna comparison
I will want to put out a max of W PEP into the antenna. The wire went up from the "ledge" to the eaves of the roof about a 15' run in that vertical section, only about 1' clear of the wall which wasn't very smart to begin with I think and then up to a tree that stands 20' - 25' in height. This run of the wire was in the clear, not lying on top of tree branches which left 26' of wire snuggling among tree branches, with the far-end of the wire tied off to the branch of another tree, leaving enough slack in the wire to accommodate swaying of trees.
Now, there appears to be conflicting pieces of information out there when it comes to the use of grounding at the feed-point and RF chokes. Adding confusion to discussions surrounding RF chokes is the fact that sometimes the terms " Current Balun" and "RF Choke" are used interchangeably. I have reviewed some very good presentations on the above though which is helping me see more clearly and I won't go into this and I wouldn't be able to do a good job at it any way.
Are you using a dedicated ground rod at the feed-point and if not, why not? Two chokes in case the antenna wire runs parallel to the coax. A second manufacturer recommends using a ground-rod at the feed-point but NO RF choke at the feed-point but rather have one just before the entry point of coax into shack.
I hear from some people that adding a ground rod at the feed-point would "kill" the antenna! Would it be "best" to have the feed-point very close to the entry point of feed-line into the shack as this way you have a very short run of coax that would be in the RF radiation field of the EFHW antenna, helping minimize RFI issue? In conclusion, I would like alternative 5 above, but I can't do it due to the antenna becoming more obvious and visible.
What I can do is have the far-end of the wire slope up to about 40' using a fiber-glass pole. Likely, I would need to tape a portion of the wire down to the pole, but in that case the angle of the wire in relation to the ground would be acute, perhaps on the order of 60 degrees.
Angles less than 90 degrees may introduce resonance issues though. The "only" other alternative would be to have about 26' of the wire's far-end tied off to the branch of another tree with some of the wire likely ending up "draped" over yet other branches. Awaiting feed-back from those of you who have successfully deployed EFHW antennas in challenging situations. Best 73 de Juha - NI2M. NI2MJan 8, End fed half wave antennas are notoriusly hard to feed.
I treat them like random wires when end fed.