An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. So, I embarked on testing it for myself. 2015. Most informative and appreciated. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Thanks! How does this SWR meter works? Software Engineer - EDI - salary.com The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. To explore parameter space a little, I modeled a couple of lengths for the counterpoise and see how the wire is resonant across the band when fed with various impedances at the driven point. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. The next important parameter is the parallel resonant circuits resonant frequency. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Contact Commercial Coils But before we do, let us look at the insertion and transmission loss that the VNA is reporting. This article will not address that antenna type. Of course, if both ends are raised higher, it will produce a more efficiently radiating antenna, but the portable and temporary installation is always compromised by conditions given by a location and its restrictions. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. I made one quite similar to it but 3T Primary with #16 speaker wire (2 parallel wires) and 15T Secondary close wound just using about one-third of the circumference of the 2 inch toroid. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. Further if your antenna requires a biggeer counterpoise on some bands, you can increase the size of the radiating element or improve your Tuner by using fine tuning capacitor or altering the coils slightly by varying the coil windings (compressed/spread out) slightly. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. Evaluating it at a we get: which gives the power dissipation simply in terms of the heat capacity, cooling time constant and the temperature difference from ambient. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! Jim, do you mind if I add your email and my answer as a comment to the article? In my research on End Fed Half Wave (EFHW) antennas I found that nearly all have a capacitor in the primary (rig) side of the transformer. = 258 * 10^-12. Be cautious, such voltages may cause a quite painful skin scorch. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. 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. Then record the change in temperature recorded at the core from the probe, and the elapsed time so I could corrected for not reaching perfect equilibrium. The SWR was measured for each of the three antennas across the CW portion of the bands. Selecting the variable capacitor that can be varied from this minimum to maximum capacity, will allow tuning to resonance for 40, 30, and 20m bands at each of the switch position of the tuner. What are its disadvantages? Im not interested in trialing coil-loaded dipoles at the minute (from my limited reading bandwidth can be a real issue) so the options I like include: 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. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. It turns out that we can easily measure the effective parallel secondary capacitance by looking at the primary self resonance when the secondary is open. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. Hence, we need to move along and start to include the antenna with our testing. PDF MANUAL: ENDFEDZ ALLBAND-KW 80-10 EFHW 1KW ICAS ANTENNA - Vibroplex Independent Medical Evaluation - IME | Cynthia Hennessey A method for estimating the impedance of a ferrite cored toroidal inductor at RF. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. View the job description, responsibilities and qualifications for this position. The worse SWR was 1:1.7 at the top end of 20 meters. The aluminum box is the logical heatsink, so I cut a few scraps of aluminum to make a thermal connection to the bottom of the box and to the lid, adjusting with aluminum shims so that when the box lid is screw down, the entire thermal assembly, with the cores in the middle, is under a little compression. A week or two later I started to notice an occasional knocking sound inside the house. Intro EFHW Compensation Coil Experiment Steve Ellington 10.3K subscribers Subscribe 29K views 4 years ago The little coil helps place the EFHW resonance points where we want them. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. Multiband End-fed Half-wave EFHW Antenna - VU2NSB.com I mentioned in the reference article that the metric A/l captures the geometry, the larger it is, the fewer turns for same inductance / impedance. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. The overlaid VSWR plots are shown below. I have an EFHW and the SWR is acceptable on all the bands with the exception of the WARC bands which is to be expected since the harmonic relationship is different. As it turns out K1RF had similar questions about the capacitor and published data showing that the capacitor does improve SWR performance at frequencies higher than 20 meters. I would mention first its ease of installation. So far so good. These dimensions were derived from modelling the antenna in EZNEC. PDF shortened multi-band End-Fed Half Wave (EFHW) antenna for 80-10m I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned -- The experiments have been performed, check it out! RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. Thirty turns #28 are wound on the two FT114-43 cores. A 100pF silvered mica was connected in shunt with the transformer . The results are presented below. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. The technical storage or access that is used exclusively for anonymous statistical purposes. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. of the wavelength. This illustration provides a graphical view of approximate comparative difference in expected Common-Mode-Current (CMC) that could flow on the transmission line to undermine the overall performance of the antenna system. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Is it any good? Pocket-tenna core is finally done! Wire and compensation coil being It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? And of course, a counterpoise with various lengths. Hence after about 3pF of output capacitance, the source will have a hard time charging up that capacitance before it is time to start discharging it. The antenna is effective and the materials and construction are of a very high quality. This will yield the maximum capacity of the variable capacitor. Cmzett: Weince joseph How can we help? PDF MANUAL: ENDFEDZ 40-10-KW EFHW 1KW ICAS ANTENNA - Vibroplex From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. I suspect that a small coil near the transformer is generally a good idea, whether it is my transformer design or others, since it is very difficult to get the antenna wire out of the box without incurring some excess capacitance. I assume you know the GNARC source for EFHW antennas. VSWR<1.8 over all of HF. The above illustration displays a typical set of Azimuth and Elevation sections of the radiation patterns that one might expect from a horizontally configured EFHW Wire Antenna deployed at an average height of 40 ft. above ground level (AGL). Generally a loading coil has far more inductance and shortens the length of the antenna significantly. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. In an urban area we are much more restricted, especially if we need to be stealth about it. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. So, how to construct an end-fed half wave antenna? At this point, I'm leaning towards the EFHW, but any of these antennas seem . It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. The radiation pattern of this antenna on most bands produces multiple lobes. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. Firstly, bandwidth on 80m is restricted to about 80 kHz at . A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. application of Kirchhoff's current Law on a typical EFHW antenna configuration. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. Highest frequency = 14.350 MHz. PDF MANUAL: ENDFEDZ ALLBAND-KW 80-10 EFHW 1KW ICAS ANTENNA - DX Engineering Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network. Ive been thinking about getting an antenna up for 80m, and Ive come across a number of options that interest me and would suit the space I have available realistically no matter what I go for it will be a very compromised antenna, but still much better than none. One end is about 5 meters high on an extended fishing pole. Now I just need to build or acquire a decent radio to utilize this new antenna. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. The negative effects of local QRM on an, How does antenna radiation occur? Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. Because of the division of power between the 3220 resistor and VNA input, there is effectively an attenuator of -10*log(50/(50+3220))=18.16dB, so |S21| has a component due to this division. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. Above 7MHz, there is very little temperature dependence at all. Trapped 20/30/40 Meter EFHW Antenna - AI6XG Geeksite The SWR results are as follows: Yes, indeed EFHW antennas are very useful for SOTA or other field operation. Very interesting design. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. I used the coil inductance calculator at 66pacific.com and after a few tries came up with 83 turns over a length of about 83mm as shown below. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. Is FT8 popularity growing at the cost of SSB Phone and CW? They will be adjusted for resonance at or close to the CW portion of the bands. After doing the ferrite transformer scaling experiments last time, and learning a bit more about what matters in these transformers, it was time to make a stab at designing one. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. 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. The SWR was low, but not unity, so the peak voltage was lower than the 50 ohm match value when measured with the high-Z scope probe. Radio Transceiver S-Meter Pitfalls to avoid, Atmospheric impact on VHF Radio Propagation, Terrestrial VHF Radio Signal Coverage LOS, Terrestrial VHF Radio Signal Coverage BLOS, HF Surface Wave Propagation (Ground Wave). To be safe, better not get much above 120 C. Saturation of a warm core happens near 0.2 T (2000 g) and if you dont want to deal with significantly reduced permeability, then better to limit to 0.1T. The second smallest number I measured was 2.7pF, derived from the self resonance at 2.72 MHz with the magnetizing inductance (measured at 25.8 H) with the secondary open and the output wire folded to a small 1/2 length. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB - qsl.net If you stare at the above frequency sweeps you will discover a few things. Apply for the Job in Software Engineer - EDI at St. Louis, MO. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. Workers' Comp. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. Above, the magenta curve is measurement of a real transformer from 1-11MHz with nominal resistance load and three compensation options: cyan: 0pF, too little compensation; magenta: 80pF, optimal compensation; and. The impedance matching circuit is essentially a simple parallel resonant LC circuit. It is not necessary to calculate the above; the results are sown in the following table. One way or another there is always a counterpoise involved if the antenna is tuned correctly. Based on a 2014 survey, the most popular antennas for SOTA (Summit On The Air) activation are the following (see sotabeams.co.uk/blog/5-most-popular-hf-portable-antennas for details): Let us not confuse the End-Fed Half Wave antenna with the Random Length End Fed wire. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. Don't sweat the digits to the right of the decimal point too much, the SWR readings changed as the feed height and droop of the antenna changed. = .000001 / 3868.88 It is likely that next time the tuning may be set according to the already found positions, and it will not be far off, requiring only slight adjustment. If we wish to limit the ferrite temperature to 130 C, then assuming ambient temperature of 30 C, we can tolerate a 100 C temperature rise. Of course, you will need to find your tuning positions and apply your own position scale. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. It is important to consider the voltages on this tank circuit. 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. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. The End-Fed Half Wave Antenna a bit Differently I particularly want to know how counterpoise affects the common mode currents on the coax. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. There's seemingly conflicting information out there, such as on QRZ the consensus seems to be to either use no choke on the coax, or choke it some ways away from the feedpoint - WA7ARK recommends .07 wavelength, which is about 9' on 40M. Make sure the first wire is wrapped evenly around the whole toroid. % Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. Best regards and thanks again for your comment. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? How-To: Make a Multiband EFHWA for Amateur Ham Radio The parasitic reactances near the feed-point also vary between installations. I also will ask, why didnt it work for you. This reveals we only need to compensate for the reactive component. As I reexamined my formula, you pointed it out correctly, there is an error in it. nanoVNA-H can firmware be updated if it has a broken USB socket? With tension on the antenna wire, you can just roll the coil up/down the wire to try different positions as you are optimizing for a particular band. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). I may try to bring down the 20, 15 and 10m bands at some point, either with a small coil 2m from the feed point or with a short section of wire as a compensation lead added at the feed point as shown in the video below from Steve Ellington. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. . ENDFED/EFHW Antenna & Choke - F5NPV - V85NPV The equation should have a 10^6 and not 10^-6 in the nominator. This gave me an effective coil diameter of 40.5mm. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. Lowest frequency = 7.000 MHz. I was curious why this capacitor was added to the transformer. This can then, fed with coaxial cable, in many cases be . Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. Looking at several builds and discussions, such as commercial antennas (e.g. y73s de Michael DL9SKY, Visszajelzs: The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Az e-mail cmet nem tesszk kzz. The resistance (real) component of the impedance is right where we want it near 50 ohms. The usual problems of having the multiple band resonances all line up appear here with the end-fed design, similar to the same issue with off-center-fed designs. There are many resources online that explain the details better than I can, so Id suggest doing your own research if youd like to build one for yourself. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? I found that sometimes the multimeter that was measuring the temperature would give unreliable information when RF was present, so the off periods provided regular intervals for measuring the temperature. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. . The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Feeling brave, I decided to tape my coil up and solder connectors on and hope I would be one of the lucky ones who wouldnt need much coil adjustment (will I be right??). I have been searching the internet for a very long time (AA5TB, VK3YE, SOTA Reflector, among MANY others), and your posting finally made clear for me the many questions I have had. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . coil inductance calculator at 66pacific.com. The antenna is up. For the last step, I put together a RF choke to use between the radio and the feedline. The SWR for the 20 meter EFHW antenna was < 1.2:1, The SWR for the 40 meter EFHW was ~1.4:1 for 40 meters and 1.2:1 for 20 meters (full wavelength), For my 20, 30 and 40 meter EFHW antennas I will not use a capacitor in the primary. In his article, I will try to bust some of the myths associated with Inverted. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. Measurements were made on the unmounted transformer with just a ~2 inch length of lead from the secondary to the 2450 load and sampling resistor (jig connections as shown in the photo above). For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. Can I get away with no capacitor in my design? This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. end fed half wave antenna - awsh.org Can you give me an idea for your 100 W version, you built for 80/60/40 m. The original coil is designed for low power portable applications. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. It depends on the selection of the inductance and the capacitor values. I've always had issues with 10m loading up properly so I'll also be adding a compensation coil 78 inches from the feed point on the wire. What are the advantages and disadvantages of the end-fed half wave antenna? Im very happy with the result. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Lets call this element the LoadAttenuator. There are many good descriptions on the net about this type of antenna. The maximum B field in the core is proportional to the imposed voltage, as: where A is the cross sectional area of the core, f is the frequency and N is the number of turns. SWR for 80-10 meter EFHW with no capacitor, SWR for 80-10 meter EFHW with 100 pfd capacitor, The above data from K1RF shows that the SWR for 20 meters (my dark red markings -, I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned, 40 meter and 20 meter (full wave) SWR with no cap. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. This antenna is working for 80,40,20,10 and 6m bands. 100W on a Wire Antenna - Is it good enough for DX? The antenna is effective and the materials and construction are of a very high quality. From this article one may build a 40, 30, 20m end fed half wave antenna, with no special parts needed, or no special skills required. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. Nagyon j ez a cikk. I got the, http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html, End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil. 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? In comparison to the EFHW antenna, a simple dipole offers a far better prospect. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. I came up with a very simple way to build these coils on the antenna wire that proved quick and easy to change and test, involving small piece of PVC pipe and a piece of Velcro shown below. The cooling curve I measured is shown below. Im very pleased with that indeed. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. Nevertheless, the EFHW antenna had in the Read More, SSN, SFI, Solar Data for HF Radio Propagation Here are some of the important Solar activity parametric data that are responsible for influencing the behavior of the Ionosphere on earth. Thanks for your comments. The technical storage or access that is used exclusively for statistical purposes. I settled on a compact secondary using #28 wire. It will present its parameters, so anybody with basic home-brew skills will be able to build it.

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