It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. Frank VK1VK. I would mention first its ease of installation. I used the 14g enameled wire and wound it on the FT240-43. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. Some website features may not function optimally without cookies. It is best to make the impedance matching adjustable, using switched transformation ratio. Your article was well written and very informative, thanks. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. There are many good descriptions on the net about this type of antenna. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. Very interesting design. As is often the case, packaging was determined by what boxes I had laying around. It will present its parameters, so anybody with basic home-brew skills will be able to build it. 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. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. Next, I started winding the transformer. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. On the transformer, I added a few wingnuts to tighten down the antenna wire. Wrap the first wire around the toroid 27 times (I used a black wire for this). Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. The End-Fed Half Wave Antenna a bit Differently, The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Ismerje meg a hozzszls adatainak feldolgozst, 40 M R/7E azaz a kirlyi ejternysk rdillomsa, jra megy az SSTV tjtsz 144,500 MHz-en. Firstly, lets estimate at 3.6MHz minimum number of turns to ensure that magnetising conductance is less than about 0.002S (for better than 90% core efficiency). For the transformer, a T130-2 toroid will be sufficient, on which we wind the seconder with multiple taps, as shown in the below table. Note the material 43 hysteresis curves shown below for 25 C and 100 C has a smaller open area (and hence lower losses) at the higher temperature. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. I assume you know the GNARC source for EFHW antennas. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. = 258 * 10^-12. 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. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. VSWR<1.8 over all of HF. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. It should be no surprise that 80pF is close to optimal. Above is a thermograph of the transformer at 20W input at 3.6MHz. High Q, hence low loss. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. In theory, the examination is supposed to be used to help clarify your medical condition and . It not a loading coil. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. . After acquiring a MTR3b for SOTA activations I decided I needed a different antenna than the End Fed Random Wire (EFRW) or the speaker cable 20 meter dipole I use with my KX2. 2006. 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. Make sure the first wire is wrapped evenly around the whole toroid. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. The 2 coils are 35uh and 90uh. But systems that work better increase the prospects of contacts. All Rights Reserved. = 1/30.e6 = 33 nS. 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! The antennas are set up as a sloper as in my SOTA outings. I drilled a couple of holes at each end of the former, a small one for the wire to pass through and a larger one for a bolt and wingnut for wire attachment as I wanted the end result to be portable across different antenna projects. The above data from K1RF shows that the SWR for 20 meters (my dark red markings - SWR scales differ in each graph) is about the same with or without a capacitor in the transformer primary. 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. Show more. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. Which begs the question what happens when you attach the antenna? VK1OD.net (offline). This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. Connected to the packaged transformer, I ran some SWR sweeps with just the bare wire and various configurations of small coils to act as band-tuning compensation. Cmzett: Weince joseph How can we help? http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. I checked the wall brackets and mast, but all the fixings were nice and tight. The parasitic reactances near the feed-point also vary between installations. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. These, in turn, are instrumental Read More, Learn CW Morse Code Lesson Set 2 This is Lesson Set -2 in our multi-part series of CW Morse Code hands-on tutorials where we will introduce numerals and a few important punctuation marks as Read More. When the transformer was mounted in its box and the output connected to an antenna connector feedthrough, the observed capacitance increased dramatically to about 6.0 pF. This reveals we only need to compensate for the reactive component. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. Throw one end of the antenna wire, extended with a rope, as high as you can on a three, and walk away with the other end and attach it to the tuner. Dutch radio amateurs in particular have been active in this area: John, PD7MAA's blog - http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html Jos van den Helm's (PA1ZP) article published in Radcom: "A 3- or 5-Band End Fed Antenna", February 2016, Radcom, published by the RSGB in the UK. 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. i liked it a lot, you give good ideas, many thanks. Note that building loss into antenna system components is a legitimate and common method of taming VSWR excursions, eg TTFD, CHA250, many EFHW transformers, but in some applications, users may prioritise radiated power over VSWR. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. See the table above. As you stated early in your posting, I also have found 99.99% of all posting on the internet tell you WHAT they did.not HOW they determined the specific design criteria. So far so good. The band compensating inductor placed on the wire is another story. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. I needed to add an additional coil (approx 12.5 uH) about . Thanks! The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. Since the tuners location is best if it is handy for the operator, one end of the end-fed antenna is also close to the operator. (LogOut/ When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. We also know, that both ends of the half wave antenna will have the highest voltage, thus impedance, which may reach up to several kilo-ohms. A week or two later I started to notice an occasional knocking sound inside the house. This provides proper insulation from the relatively high voltages on the seconder winding. The resistance (real) component of the impedance is right where we want it near 50 ohms. If not a lightning strike, I will write an article about the experience as well. The computation method is also touched on. ROB@COMCOIL.COM Being a more efficient design that some, it might result is a wider VSWR excursion that those others as transformer loss can serve to mask the variations in the radiator itself. Note that there is some uncertainty in the measurements, but we can be confident that the loss is no where near the figure estimated for the FT82-43 design. Thirty turns #28 are wound on the two FT114-43 cores. The final turns ratio turned out to be 3:29. And of course, a counterpoise with various lengths. of the wavelength. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. IIRC they call it a "compensator". Zin=46.52+j6.72. My favorite SOTA antenna is the End-Fed Half Wave Antenna. They will be adjusted for resonance at or close to the CW portion of the bands. Thanks again Jim. Hence, we need to move along and start to include the antenna with our testing. Some say you do not need a counterpoise, but that is false. nanoVNA-H can firmware be updated if it has a broken USB socket? The toroid with its many taps may be soldered directly on a multi-position switch. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. On one end, I added a ring terminal to connect it to the transformer and on the other end, I connected an electric fence insulator. As I reexamined my formula, you pointed it out correctly, there is an error in it. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. Let us touch on some necessary theory to begin with. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. Be sure to take a look for additional analysis and conclusions. 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. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? 2015. 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??). It is important to consider the voltages on this tank circuit. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! We do not know what the actual impedance will be at the end of the antenna radiator. I tossed the line as far up as I could in a tree. 5) It is very hard to avoid stray capacitance on the output. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. This will also be handling 100W. 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. Does your station desperately need a good RF ground to behave properly? I particularly want to know how counterpoise affects the common mode currents on the coax. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. The technical storage or access that is used exclusively for statistical purposes. 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. Nagyon j ez a cikk. Above, 3t on the primary delivers Gcore<0.002S. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . 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. Assuming, most of us use the 40/30/20m band for HF SOTA activation, so the following table shows the SOTA frequencies, and the calculated half wave radiator wire of the antenna. Apply for the Job in Software Engineer - EDI at St. Louis, MO. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this).
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