73 A Portable 7-Band End-Fed Half-Wave (EFHW) Antenna Stephan M. Schmid, HB9EAJ Version 1.2 – August 17, 2021 Figure 1: A typical inverted-L EFHW antenna setup with one … 2020-09-25a OK, I think I am zeroing in on a design. Compensation capacitor 80m: current is max at center of long wire 40m: current is min at center of long wire Capacitive reactance makes antenna shorter only on 80m not on 40m on up Capacitor becomes a short on higher bands Position juggled with compensation coil. It might need ~1.2microHenry compensation coil at ~2m from the transformer to bring 10 meters in though. An antenna loading coil is an inductor placed in series with an antenna element in order to lower the antenna’s resonant frequency. 1. When I'm measuring the half way point on my EFHW, looking for 67', how do I factor in the compensation coil on the MyAntennas wire? Typically, a parallel tuned circuit is used at the end of the antenna with the feed line link coupled or tapped to the coil in the circuit. Yes, there is a coil a few feet from the box but it is NOT TRAP, it is no secret as well, actually, everything in this antenna was published and patented by few people a long ago. Steve traces the history of this "classic" antenna, discusses its basic theory, and offers suggested design and construction tips. I carefully tuned my QRPGuys EFHW so it had good SWR across 40, 20, 15 and 10 meters without the coil attached. Thanks to Steve Ellington for this superbly produced tutorial on the modern half wave multiband HF antenna. Resonance may also be observed at … There will be some variation between different batches and sizes of materials. The SWR figures were as follows: FT240-43 132ft/100pF capacitor Look at the compensation coil slide. A standard dipole antenna is resonant if constructed with a length of one-half wavelength. I can give a link if you need. An EFHW (End Fed Half Wave) antenna for 160-10m band operation ... you can find on the Web, this could be operated from 10m to 40m, and in addition on 80m by adding a 110µH loading coil + tail wire of about 2m length at the end. Cut the bifilar pair (braided magnet wire) to length, sand them, and solder them to- gether. Obviously, an EFHW antenna has a "half-wave" length only at one specific frequency. Typical end-fed antennas are supposed to work on multiple ham bands, so the transformers must be broadband. It is called the EFHW-8010. Having selected a candidate core, the main questions need to be answered: how many turns are sufficient for acceptable InsertionVSWR at low frequencies and core loss; and. EFHW-8010-1K-Plus typical SWR at 25-30 feet above the ground fed with 50ft of RG8X coaxial cable *Amateur Radio Emergency Service® (ARES), ALE-Automatic Link Establishment (HFlink) ... so I cut a wire and wound a coil for a 40 M version in case space was an issue. At home my Imax2k does all the 15, 12, 11, and 10m work, but as a portable I was looking for the claimed all band wire. If fed at the end (a.k.a EFHW), antenna impedance is in the 2000-4000 ohms range. 30 Watts QRP, 80-10 Meters. The EFHW’s SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. FT240-77 0.74MHz. Whether you’re QRP backpack, vacationing, emcomm station, or an antenna neighbors will never see, MFJs got an EFHW for you: MFJ -1982LP, $49.95. I do have the little compensation coil for the upper bands inline on the wire. The SWR for the 20 meter EFHW antenna was < 1.2:1 End-Fed Half-Wave antennas, Grounding & RF Chokes | QRZ Forums He also suggested that adding a turn or two to the coil would bring the SWR down. . Optimum Performance. Start by wrapping the wire around the toroid. Applying a feed to any antenna in NEC or any electromagnetic simulation software is about a simple a task as can be conceived by placing a “source” of near infinitesimal size inline with a dipole element. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). I.e., a turns ratio of about 1:7 to 1:8. I have written several articles on design of high ratio ferrite cored transformers for EFHW antennas. The coupler is mounted 2 … It requires a high impedance matching device: Either a tapped resonant circuit, a Zepp type coupling circuit, or a high impedance ratio UNUN (49:1 or 64:1) It can be used on multiple bands. This gave me an effective coil diameter of 40.5mm. “Rolf, KE1Y, has a EFHW 80 – 10 and it’s wire has broken near the loading coil. 40-160m EFHW kite antenna. Compensation. At FT82-43 matching transformer for an EFHW I wrote about the likely losses at 3.6MHz of a common design using a FT82-43 ferrite core with a 3t primary. When I go to 80, it becomes a quarter wave. Here are my references for some common ferrite materials. This inductance has the effect of bring the resonances a bit lower, particularly on the higher bands and thus improving the match. EFHW-8010-1K is the ultimate MAGIC antenna! Instead, this shifts everything down and makes it very easy to tune 10m. The G0KYA/PD7MAA/IK0IXI EFHW extension to cover 80m calls for a 110uH coil placed at the end of the EFHW, with a further 2-2.5m of wire beyond this. You won’t find a lighter, more portable EFHW or EFRW Matching Unit. Quality components with a novel design that simplifies the build process. It is simply a half wave end-fed on 80m which will resonate on all multiples of that frequency, loaded with a small inductance near the feed end. I assume you know the GNARC source for EFHW antennas. This light weight wire (NSN 6145-01-047-4345) has a breaking strength of over 200 pounds. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Image credits to G0KYA’s blog I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. Once the winding is tight, make sure there is at least eight feet of wire between the compensation coil and the end. Figure 20: Nominal dimensions of the multi-band end-fed antenna. End-fed horizontal wire, an EFHW, offers the perfect solution for a wide range of ham activities. End-fed horizontal wire, an EFHW, offers the perfect solution for a wide range of ham activities. Whether you’re QRP backpack, vacationing, emcomm station, or an antenna neighbors will never see, MFJs got an EFHW for you: MFJ -1982LP, $49.95. 30 Watts QRP, 80-10 Meters. MFJ-1984LP, $39.95. 30 Watts QRP, 40-10 Meters. There are some changes if you want to do a 160m EFHW antenna. The coupler is a tuned impedance transformer, not an antenna ‘tuning’ unit. In spite of what some manufacturers will … 30 Watts QRP, 40-10 Meters. Mechanical Issues with EFHW Antenna. Quality & Simplicity. CK, your explanation rings truer than any of the hype/ads I have seen about the 49:1 EFHW. First, you need 260 feet of wire and no coil on the antenna. Compensation (Optional) coil EFHW Counterpoise Current flowing into the antenna's end must be equaled, at that end point, by the same amount of current flowing into a ground or counterpoise of some type. Stick to the above, and it should be a sure thing! In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. ... At these low frequencies, you also don’t need a compensation capacitor across the input of the transformer. Use a 200 pf capacitor instead of 100 pf. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. FT100-33 7MHz. I did some more reading about end-feds and I’m thinking that perhaps adding a short counterpoise might be something to try, too. FT240-31 3.5MHz. A vertical antenna (effectively half a dipole operating against a ground plane) is resonant at one-quarter wavelength. Then it occurred to me that some people add a coil and short extension to the 40-10 EFHW so it will cover at least some portion of the 80/75 meter band. So this afternoon I began experimenting with that idea. My mission to find a suitable coil form led me to the Costco Multivitamin jar! But if you can plot the results graphically you can easily identify the 'signature' of each material. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. If playback doesn't begin shortly, try restarting your device. This was a little bit of a compromise as the last 20ft of the antenna had to run down a fence to fit it into the garden. This implies a 49:1 impedance transformation from 50Ω, so a turns ratio of 7:1 is required for the transformer. A half-wave at the lowest band of interest will also work well on all harmonically-related bands which has become particularly attractive to those wanting a quick portable wire antenna. So an impedance transformation ratio of about 1:50 to 1:60 is needed to get down to 50 Ω. Crush DX from the mountain tops like you never have before. Update: Full size 132ft EFHW For one month I replaced the 66ft wire and loading coil and replaced it with a full 132ft of wire, connected to the FT240-43 balun. Make sure the first wire is wrapped evenly around the whole toroid. With a 49:1 or 64:1 UNUN, no tuning It is made of 4 tinned copper wires for low resistance and 3 galvanized steel wires (for strength) in each conductor, “zip cord” style. He wants to know if there is a better way to have the loading coil so it would be so likely to break and Dave’s view of the EFHW.”. MFJ-1984LP, $39.95. Seriously disagree, efhw works well on several bands (80-10, 40-10), and should use 49:1, as nominal impedance of efhw is ~2240 ohms, and 49:1 matches it to ~50 ohms. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. Steve presented this topic at the Lawrenceville, Georgia Techfest. The insulation is rated at 1000 volts RMS. A half wave vertical for 21MHz. Do I count the … The final turns ratio turned out to be 3:29. The 2 conductors are tied together at each end. The transformer should be 3 - 43 mix cores with 3 primary and 21 secondary windings (up to 30 depending on SWR). The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. A special case of this, is the End-Fed Half-Wave (EFHW) antenna. I used 3 stacked FT50-43 cores which made for a very compact transformer that I housed in a 20mm conduit joiner with end caps. After all, the entire wire element is on one side of the feed-point which happens to be at the end. So, where will the counter-balancing RF current to fulfill the Kirchhoff's law conditions come from? This is precisely the issue. A counter-balancing Kirchhoff's current must somehow be forced into the feed-point node for the EFHW antenna to work. I found empirically that the impedance of this antenna is about 1800 to 5000 ohms when things are adjusted properly. EFHW as a multi-band antenna EF resonates on all harmonics, Resonance not exact integer multiples Requires Compensation coil, about 6ft from transformer Aligns the SWR dips on harmonics Coil makes it “longer” Show simulation Show Patterns wa7ark 25 wa7ark 26 wa7ark 27 Move the first SWR null to 75m Portrayed below is a complete and self-contained NEC model of one popular form of the end-fed half-wave dipole antenna. This is known as the compensation coil. So, a "multi-band end-fed half-wave" antenna is actually a bit of a misnomer... A "half-wavelength" radiator has a high impedance ( = high voltage, low current) at the feedpoint. If 80 meter resonant point is too low (for SSB) on 80 meters You can add a small capacitor roughly in the middle of the antenna wire. Value 250pF-500pF. This is mounted at a high current point. The “blue” ceramic high voltage caps work. This cap has little effect on the higher frequency bands. 20 Shortened EFHW Antennas 21 6.65 metres of wire on a 9 metre fibreglass pole. It not a loading coil. point to the loading coil is 20.2m and this sets the 40m resonance at 7.1MHz, which in turn dictates the responses of the harmonically related bands 14MHz, 21MHz and 28MHz. Then I added the coil with a ten foot extension wire and a way to fold it back so I would have lots of room to adjust. The SWR for 30 meters, 1.05:1, was the lowest of all three antennas since the transformer was tuned for impedance match at 30 meters. Feeding a 21MHz half wave. A Smith chart view of EFHW transformer compensation. Wrap the first wire around the toroid 27 times (I used a black wire for this). As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. The antenna generally has a high impedance (several thousand ohm) on most bands. Do not cross over the winding.
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